Apollo Fire Alarm Design Guide PDF - PDFCOFFEE.COM (2024)

Speciﬁers’ Guide Section

A guide to ﬁre alarm systems design

www.apollo-ﬁre.co.uk

INTRODUCTION TO THE GUIDE Apollo Fire Detectors has created this guide as an aid for use by all who have responsibility for specifying or designing systems incorporating automatic fire detectors. It is intended as a guide to good practice but does not aim to be an exhaustive guide to fire design standards or codes. The guide is to assist in design and specification of fire systems. Notes on the text are indicated by the convention of a superscript number. An example of this might be ‘codes and standards2’. Notes appear at the foot of the relevant page. For any queries concerning technical matters, please contact Apollo’s Product Support Department (email: [emailprotected]). All other comments and suggestions should be directed to the Marketing Department at Apollo (email: [emailprotected]).

All the information is given in good faith but Apollo Fire Detectors cannot be held responsible for any errors or omissions. We are grateful to readers who notify us in the event of any need for corrections.

APOLLO FIRE DETECTORS Apollo Fire Detectors has specialised in the design and manufacture of high quality fire detection products since 1980. In that time, the company has broadened its capability from a straightforward focus on conventional fire detectors to include the manufacture of sophisticated analogue addressable detectors and interfaces for monitoring and controlling equipment in fire protection systems. Apollo is an Open Protocol manufacturer and over the past 30 years has developed trusted partnerships with over 70 Panel Manufacturers who supply panels incorporating Apollo’s open, digital protocol, meaning the customer is free to choose different companies to service or maintain the system. All Apollo products are forwards and backwards compatible, giving customers the added peace of mind that they will be able to source fire detectors that are compatible with their existing devices. Our Product Lifetime Guarantee provides a warranty on our products, which for detectors is10 years (CO detectors, 5 years). The guarantee supports our recommended working life of the product and endorses our commitment to providing reliable, quality fire detection products. Apollo is part of the Halma group of companies. Halma is a FTSE top 250 listed PLC with over 40 subsidiaries worldwide, all engaged in specialist engineering activities.

Apollo Fire Detectors Limited 36 Brookside Road Havant Hampshire PO9 1JR England

Tel: +44 (0)23 9249 2412 Fax: +44 (0)23 9249 2754 Email: marketing@apollo-fire.com productsupport@apollo-fire.com www.apollo-fire.co.uk

Speciﬁers’ Guide

Section 1

Contents

LIST OF ABBREVIATIONS

OPEN, CLOSED AND DIGITAL PROTOCOLS – WHAT DOES IT ALL MEAN?

Section 1 DESIGNING A FIRE PROTECTION SYSTEM Using a code of practice Manual and automatic fire detection and alarm systems Doing a risk assessment Recommendations of BS 5839-1:2002 (as amended) System components About BS 5839-1 Fire alarm system projects The design process The installation process Communication with the fire brigade Limitation of false alarms The commissioning process User responsibilities Extensions and alterations to existing systems Servicing and maintenance

1.1

SYSTEM PLANNING AND CONSULTATION

1.2

SELECTING THE CORRECT CATEGORY OF SYSTEM AND SYSTEM TECHNOLOGY Category of system Proposing the system category Prescriptive categories Non-prescriptive categories System technology Non-addressable systems Analogue addressable systems Intelligent systems

1.3

SYSTEM ZONE CONFIGURATION Detection zones Alarm zones Non addressable versus analogue addressable zones Visual indicators on detectors Remote visual indicators

CONTENTS

10 10 10 10 11 11 13

15 18 20 20 21 21 22 23 24 24 28 30 30 30

Speciﬁers’ Guide

Section 1

Contents

CONTENTS CONTENTS

1.4

1.5

SELECTING THE CORRECT DETECTORS Types of fire detector Choosing the right detector Smoke detectors Heat detectors Flame detectors Carbon monoxide (CO) fire detectors Multisensor detectors General detector choices

LOCATION AND COVERAGE OF DETECTORS Detector spacings Flame detection Duct detection Optical beam smoke detection

32 33 33 35 37 37 38 39

45 50 50 50

1.6

MANUAL CALL POINTS

1.7

AUDIBLE AND VISUAL ALARM REQUIREMENTS Audible alarm devices Calculating sound pressure level Visual alarm devices

54 54 57 61

1.8

CONTROL AND INDICATING EQUIPMENT/CONTROL PANEL EQUIPMENT

1.9

POWER SUPPLY REQUIREMENTS Standby times Standby times for Category P systems Standby times for Category L systems Calculating required battery capacity

1.10 CIRCUIT DESIGN Detection circuits Upgrading a non-addressable system Alarm device circuits 2.

INSTALLATION AND CABLES Installation Variations from BS 5839-1 Variations to contract Cables and wiring Use of 4-core cable COMMUNICATION WITH THE ALARM RECEIVING CENTRE

63 63 63 64 65 65 67 68 71 71 71 71 71 73 75

Speciﬁers’ Guide

Section 1

Contents

FALSE ALARMS Choosing the detector to avoid false alarms

THE COMMISSIONING PROCESS Handover

USER RESPONSIBILITIES (THE RESPONSIBLE PERSON) Keeping records in the log book

83 84

EXTENSIONS AND ALTERATIONS TO EXISTING SYSTEMS

SERVICING AND MAINTENANCE Daily Weekly Monthly Quarterly Periodically Annually Handover for each service visit

LIST OF OTHER STANDARDS UK Standards and Codes of Practice Fire Safety Risk Assessment Guides issued by HM Gov for Eng & Wales Scottish guidance on the Fire (Scotland) Act and the Fire Safety (Scotland) regulations Healthcare Standards and codes in other countries Regulations

CONTENTS

87 87 87 87 88 88 89 90 90 91 92 92 92 92

COMPLIANCE WITH THE EU CONSTRUCTION PRODUCTS DIRECTIVE 89/106EEC (CPD)

FIA APPLICATION GUIDELINES FOR CARBON MONOXIDE (CO) FIRE DETECTORS

1. Introduction 2. General guidance on the application of CO fire detectors - Important note 3. Risks where CO detectors can provide a means of early fire detection 4. Siting of CO fire detectors

5. Risks where CO fire detectors are not recommended as the prime means of detection 6. Lifetime factors including testing, servicing, maintenance and replacement

95 96 97

Speciﬁers’ Guide

List of Abbreviations

LIST OF ABBREVIATIONS CONTENTS 6

AFD

Automatic Fire Detection

ARC

Alarm Receiving Centre

ASD

Aspirating Smoke Detection

ATEX

ATmospheres EXplosive

CIE or cie

Control and Indicating Equipment

Carbon Monoxide (detector)

CoP

Code of Practice

Competent Person

CPC

Circuit Protective Conductor

CSP

Critical Signal Path

dB(A)

decibel, (A-weighted)

FD&A

Fire Detection and Alarms

F&RS

Fire and Rescue Service

MCP

Manual Call Point

PII

Professional Indemnity Insurance

RoR

Rate of Rise (heat detector)

Responsible Person

Speciﬁers’ Guide

Open, Closed and Digital protocols - what does it all mean?

OPEN, CLOSED AND DIGITAL PROTOCOLS – WHAT DOES IT ALL MEAN? What are Protocols? The term ‘protocol’, when used with reference to electronic products, refers to the way in which the products have a communication ‘language’ which is termed ‘protocol’. Protocols are often referred to as ‘open’, ‘closed/managed’, ‘digital’ and ‘analogue’. It is important to be sure what each term means when comparing different types of fire detection system.

Building Services Protocols With the development of more and more products that need to communicate with each other, in particular products used for building services in sophisticated modern buildings, the need has arisen for protocols to be agreed across a whole range of manufacturers or even entire industries. For instance, the electrical trade has systems for switching large numbers of current-consuming devices, such as lights, by using simple loop wiring and a data transmission protocol, rather than miles and miles of cables for individual circuits. Examples of such protocols are ‘LonWorks’ and ‘EIB’. Because such protocols are available for any manufacturer to use, they are often referred to as ‘open’. The fire detection industry does not currently use such protocols and the term ‘open’ has come to mean something different in this particular industry.

Fire Industry Protocols In the fire detection industry addressable systems use control panels and detectors (and, of course, devices such as interfaces) which communicate with each other by means of a protocol. Some manufacturers offer both panels and detectors. These companies have no need to disclose the nature of their protocol to anyone, since they offer all the elements needed to provide a complete addressable system. No equipment supplied by other manufacturers is expected to be compatible with such systems, so the protocol used is said to be ‘closed/managed’. A number of manufacturers of detectors, including Apollo, make no control panels; they have built up partnerships with independent panel manufacturers and, in some cases, companies who offer special equipment, such as aspirating detection systems. The detector manufacturer determines the protocol used by the detectors and produces the information and technical data required to panel manufacturers in order to design panels that will drive the detectors. Since all details of the protocol must be disclosed, it is referred to as an ‘open’ protocol. Apollo has written agreements with many panel manufacturers to allow them to use the information which remains the intellectual property of Apollo.

Closed/Managed Protocols Manufacturers of equipment using closed/managed protocols claim that all elements (detectors, panels, call points, interfaces, special detectors such as beam detectors) will work harmoniously with each other, since it is all designed and made by the same company. The percieved implication is that a system comprising detectors and interfaces from one manufacturer and panels from another cannot work as well with each other.

Speciﬁers’ Guide

Open, Closed and Digital protocols - what does it all mean?

Open Protocols The manufacturers of the components of a system with an open protocol would reply that products from different manufacturers of fire products work just as well with each other as does, for example, a McLaren racing car with a Mercedes-Benz engine. Indeed, it may be said that there is an advantage in having different specialist manufacturers concentrating on their own skill areas.

After-sales service Whatever the arguments for either system may be, one point is indisputable: the owner of a fire protection system with a closed/managed protocol is dependent on just one supplier for all spare parts, servicing, modification and upgrade of the system, since no other manufacturer’s products will be compatible. The owner of a system using an open protocol can freely choose a different company to service the system or to supply different upgraded equipment, as well as make alterations to the system – for example, change the text of a detector or modify the cause and effects.

Analogue and digital protocols The term ‘analogue’ is used to describe a signal which goes up and down steplessly. See Fig 1. Signals that record phenomena such as the increase of smoke or heat are necessarily analogue at source and this is why fire detectors are described as analogue. For example, a heat detector will record stepless increases in temperature from a typical starting point of 20-21oC (comfortable room temperature) to an alarm level of 55oC, however fast the increase. Each point on the analogue signal indicates a particular value. The problem with analogue signals, however, is that, if, during transmission, electrical corruption affects the signal, a ‘2’ might appear as a ‘3’, for example. The description of the communications protocol as “analogue” should not be confused with the description of a fire alarm system as “analogue” or “analogue addressable”. An addressable fire alarm system is one in which signals from manual call points and detectors are individually identified at the control and indicating equipment. In practice, nearly all addressable systems are of the “analogue” type, meaning that signals from each detector are individually processed to enable a representation of its amount of sensed phenomenon (i.e. heat, smoke etc) to be transmitted to the control and indicating equipment. The method of transmission of this value may be digital or analogue, but is normally digital.

Digital signals The word ‘digital’ describes a signal that consists of a series of ‘0s’ and ‘1s’ or ‘offs’ and ‘ons’ which go to make 8

up a message in binary arithmetic. The advantage of this system is that there is a much lower risk of the signal being poorly transmitted and hence giving wrong information. Fig 2 shows the simple levels of 21, 22 and 23 (illustrated by the curve in Fig 1) as digital signals. Each degree in the example of a heat detector given in the previous section can be expressed in digital form (ie, binary arithmetic). ‘30’ degrees Celsius would then be ‘11110’ and this is what Apollo detectors would transmit. Apollo fire detectors have always used a digital protocol which has remained basically unchanged since its inception in 1986. It has been extended – in two steps, once for XP95 and a second time for Discovery – but never modified. Most detector manufacturers have now adopted digital transmission protocols. In summary, an open protocol allows freedom of choice by the specifier, the installer and the end user of the fire detection system. A digital protocol is much less susceptible to corruption than the analogue protocol and is to be preferred in a system which is life-critical.

Speciﬁers’ Guide

Open, Closed and Digital protocols - what does it all mean?

Apollo has a digital, open protocol

23 22 21

Fig 1 Analogue signals

0 9

Fig 2 Digital signals

Speciﬁers’ Guide

Section 1

Designing a ﬁre protection system

1. DESIGNING A FIRE PROTECTION SYSTEM Section 1

Using a code of practice In many buildings, automatic fire detection is a key component of the overall strategy to protect the building, its occupants and its contents from fire. To meet demands for fast, reliable detection, manufacturers like Apollo Fire Detectors have developed more sophisticated, more intelligent products - products that balance optimum performance with increased immunity to false alarms. But detectors form only part of a fire detection and alarm system. System technology has also advanced greatly in recent years. Many analogue addressable systems incorporate powerful features aimed at ensuring fast, efficient response to fire. For a system to give maximum benefit, however, it must be suitable for its intended application, and it should meet the recommendations of fire alarm standards and codes. In this Specifiers’ Guide, we aim to explain the process of designing a fire detection and alarm system and help you in specifying suitable products and components. The design of a system must usually satisfy the criteria laid down in standards and codes. These vary and it is important that you comply with standards and codes that apply in your country. However, to explain the impact that standards can have on the design process, we have included a guide to the British Standard for Fire Detection and Alarm Systems, BS 5839-11. This is presented in Part 1 of this guide.

Manual and automatic fire detection and alarm (FD&A) systems It is not possible to prevent all fires. Occasionally a fire will occur. If someone notices it, they can warn others by operating a manual call point (MCP). If a fire occurs in an unoccupied room, the fire could develop, cause damage and threaten lives before it is noticed. Automatic fire detection (AFD) with smoke and heat detectors can be used to compensate for this risk. For example, AFD in a boiler room compensates for the risk of the boiler becoming faulty and causing a fire, or AFD in a bedroom compensates for the possibility of a fire occurring whilst the room is unoccupied or the occupant is asleep.

Doing a risk assessment The Regulatory Reform (Fire Safety) order 2005 requires that the employers and other persons having control of premises must carry out, or have a consultant carry out on their behalf, a fire risk assessment. The findings of that risk assessment may require that an FD&A system be installed to give adequate warning of fire. Risk assessments are usually quite straightforward, for ordinary premises, and need not introduce significant cost.

Recommendations of BS 5839-1:2002 10

This part of the guide aims to take you through the recommendations of BS 5839-11, the British Standard code of practice for the design, installation, commissioning and maintenance of fire detection and alarm systems in the UK. An understanding of its recommendations is fundamental to good system design. It is also essential to know the code’s recommendations when specifying products and systems. Users too will benefit, as the code contains many recommendations that apply to them. In a short guide such as this, we cannot explain every clause of BS 5839-1. Rather, we aim to focus on the key clauses that govern the process of system design and equipment selection, as well as those that relate to the management of a system, once it has been installed and handed over. To fully understand all of its recommendations, we would recommend you read through BS 5839-1 in conjunction with this guide. BS 5839-1 is not the only standard relating to fire detection and alarm systems in buildings. Depending upon the application, you may find that it is necessary to comply with other standards or codes. We have listed a number of these later in this guide. Also listed are some of the standards that apply to system design in other countries. 1 BS 5839-1 Fire detection and ﬁre alarm systems for buildings - Code of practice for system design, installation, commissioning and maintenance.

Speciﬁers’ Guide

Section 1

Designing a ﬁre protection system

Most of the components used in a fire alarm system, such as the control panel, smoke and heat detectors, alarm sounders, interfaces and ancillary items have their own standard. In Europe the base standard is EN 54 and this has separate parts for each type of component, for example smoke detectors are covered by EN 54 part 7. The control panel is split into two parts, the control and indicating equipment is covered by EN 54 part 2 and the power supply by EN 54 part 4. The control panel usually houses both items, so for simplicity in this guide we will refer mainly to the control panel.

Section 1

System components

The various parts of EN 54 have been adopted as British Standards, then becoming BS EN 54 and it is these that are referred to in BS 5839-1.

About BS 5839-1 Although preceded by other British Standards on fire alarm systems, BS 5839-1 was first published in 1980. It was revised in 1988 to take account of changes in fire alarm technology and, in particular, the introduction of analogue addressable systems. The current version was published in 2002. It again recognises new developments in fire alarm technology such as carbon monoxide fire detectors, technical changes (for example, regarding the fire resistance of cables) and new concepts such as the introduction of categories of false alarms. The present standard is in a format showing • “commentary”, in italics, for information and background knowledge; and • “recommendations”, in regular font, as the parts that should be followed if compliance with BS 5839-1 is being claimed. The recommendations state, for example, “manual call points ‘should’ be located at all exits to the open air”. The use of the word ‘should’ shows that if you are claiming compliance to BS 5839-1, then you would comply with that recommendation. Recommendations do not use the words “shall” or “must”, those being used in product standards such as the parts in BS EN 54, and in various government laws and regulations. BS 5839-1 contains recommendations that apply to a wide range of different buildings. Although it covers all types of building (other than dwellings), its recommendations are general in nature. For some buildings, such as hospitals, more specific recommendations are required, and these are to be found in other codes and standards2. It is also important to remember that BS 5839-1 does not recommend whether or not a fire detection and alarm system should be installed in the first place. The need for a system in any given premises will be dependent on the type of premises. For example, it should be fairly obvious that, in a hotel where people sleep, automatic fire detection (AFD) in all rooms would detect a fire and electrical alarms could then be operated to wake the occupants so that they can evacuate to a place of safety. In a much simpler building, in which all rooms are occupied and where no-one sleeps, if fire does start, it would be quickly seen by someone and they could warn others by shouting a warning, ringing a hand bell or operating a MCP. In this case AFD may not be necessary. This process of looking at a building, judging its size, the number of people, whether they are awake or asleep, whether they would quickly notice a fire, or hear an alarm warning is all part of a fire safety risk assessment. Legislation in the UK states that a fire risk assessment MUST be done, and any organisation responsible for business premises that fails to do the risk assessment, and take appropriate action, would be in breach of the law. AFD can also be required by property insurers in order to safeguard valuable buildings and contents. In new buildings, fire detection is often an essential element of a fire engineering strategy.

2 A list of other codes and standards that relate to fire detection and alarm systems can be found on page 90 of this guide.

Speciﬁers’ Guide

Section 1

Designing a ﬁre protection system

Section 1

BS 5839-1 is a code of practice and not a specification. It contains recommendations, not requirements. As such, there is scope to vary the recommendations of the code, particularly if the recommendations are unsuitable or would lead to a system that would be difficult to install. However, there must be sound reasons to deviate from the code’s recommendations, and any variations of this kind should be agreed with all of the interested parties. It may also be the case that BS 5839-1 is specified in a contract. In this case, compliance becomes a contractual obligation. BS 5839-1 is divided into seven sections: 1. General This covers planning and consultation, and in particular, the need to specify the category of system. 2. Design considerations This covers the selection of equipment, location and siting of devices such as detectors, interconnection of system components and the methods of raising the alarm. 3. Limitation of false alarms This highlights the problem of false alarms, including what causes false alarms and how they should be avoided through careful design. 4. Installation Site work and practices associated with installing the system are covered. 5. Commissioning and handover Recommendations relating to the testing, commissioning and certification of the system are outlined here. 6. Maintenance This covers testing, services, repairs and modification. 7. User responsibilities This addresses the need for the user to appoint a responsible person to manage the system once installed and the need to keep records relating to the system in a log book. It is not our intention to follow the sequence of clauses and recommendations as they are set out in the code. Instead, we will highlight key recommendations as we take you through the process that needs to be followed in designing a fire detection and alarm system.

Speciﬁers’ Guide

Section 1

Designing a ﬁre protection system

Fire alarm system projects

1. The design process The process of designing a fire detection and alarm system involves a number of elements as follows: 1.1

System planning and consultation

1.2

Selecting the correct category of system and choosing the system technology

1.3

System zone configuration

1.4

Selecting the correct detectors

1.5

Location and coverage of detectors

1.6

Manual call points (MCPs)

1.7

Audible and visual alarm requirements

1.8

Control panel equipment

1.9

Power supply requirements

Section 1

This guide has a number of sections, dealing with the important steps involved in the progress of a fire detection and alarm system project.

1.10 Circuit design We will consider each one of these in turn in this guide. 2. The installation process In this section of the guide requirements for cables will also be discussed. 3. Communication with the fire and rescue service Automatic communications, usually via an alarm receiving centre. 4. Limitation of false alarms The responsibility for limiting false alarms is discussed in this section along with information on causes of false alarms and how to avoid them. 5. The commissioning process The process of commissioning includes handover to the user or purchaser and training of staff. 6. User responsibilities All systems require management after installation and user responsibilities are explained in this section. 7. Extensions and alterations to existing systems Design and documentation for modifications to systems. 8. Servicing and maintenance This section includes routine and non-routine attention.

Speciﬁers’ Guide

Section 1

System planning and consultation

1.1 SYSTEM PLANNING AND CONSULTATION Section 1

The purpose of a fire detection and alarm system is to support the fire safety strategy for the building in which it is to be installed. Therefore, the system design must support the fire evacuation procedures that are to be followed. The system requirements must be considered at an early stage. This is part of the consultation that BS 5839-1 (Clause 6) recommends should take place between the user or purchaser and other interested parties. Interested parties can include: - the local fire and rescue authority and the relevant building control body - the Health and Safety Executive (the body charged with enforcing workplace health and safety in the UK) - the property insurer. It is important that the system designer ascertains the requirements for the system by consultation with the user or purchaser of the system. There may also be a need to consult others such as architects, mechanical and electrical consultants and fire engineering consultants. Outside the UK different legislation and building codes apply. It is essential that the local building control and/or fire service officials or any other authority having jurisdiction is consulted. Any proposal to vary the recommendations of BS 5839-1 should be agreed with the relevant interested parties. Variations should be documented on the design, installation or commissioning certificate as appropriate. Consultation is a fundamental part of the planning of a system because it enables the purpose of the system to be determined, and allows the designer to establish the requirements for the new system. From this point, it is possible to go on to specify the category of system.

Section 1

Selecting the correct category of system and choosing the system technology

1.2 SELECTING THE CORRECT CATEGORY OF SYSTEM AND CHOOSING THE SYSTEM TECHNOLOGY Category of system

Section 1

Speciﬁers’ Guide

BS 5839-1 (Clause 5) divides fire alarm systems into a number of different categories. These relate to the purpose of the system, principally whether it is to protect life (categories L1, L2, L3, L4, L5 and M) or to protect property (categories P1 and P2). There are six different life protection categories. L1

Category L1 systems should have AFD throughout the building. The only possible exceptions are toilets, toilet lobbies, stairway lobbies, and small cupboards of less than approximately 1sq m, provided in each case, the room in question is of low fire risk (i.e. virtually no ignition sources or combustible material and no likelihood of fire spread). Detectors should be optical detectors on escape routes. In rooms, the detection would be chosen to suit the risk, without causing false alarms.

Category L2 systems should be as L3, but with additional AFD in rooms of high risk, even if they do not open onto an escape route. For example, rooms with a high probability of ignition: plant rooms, hot-work rooms etc. Rooms or areas, in which there would be serious risk to people if a fire started in the room, should also be protected with smoke detectors. All these rooms should be listed or identified so the installer knows where the additional detectors should be fitted.

Category L3 systems should be as L4, but with AFD installed in all rooms or areas opening onto escape routes. The detectors in these rooms need not necessarily be smoke detectors, but should be chosen to suit the risk, for example, in a kitchen, heat detection would be appropriate to avoid false alarms.

Category L4 systems should have MCPs and sounders as for category M with automatic fire detection (AFD), using optical smoke detectors, installed on the escape route corridors and stairways, so that occupants can be warned of fire if it reaches an escape route. Optical smoke detectors are recommended for escape routes in BS 5839-1 because escape routes themselves should not contain equipment, substances, fixtures or materials that could start a fire or add significantly to a fire, so any smoke will have travelled some distance and the smoke particles will have aged and coalesced into larger particles. These larger particles are best detected by optical smoke detectors (see a later section for a description of detector types).

Category L5 systems do not need to include MCPs, but sounders are recommended throughout the building. AFD could be designed to meet a specific fire safety objective, which may not necessitate installing one of the other categories. One simple example could be a single detector in a high risk area (e.g Boiler Room) where, if a fire occurred, it could threaten the escape route for occupants. A more complex example would be for a large building with many occupants, where the fire safety objectives can be met without following a recognised code of practice. For category L5 a specification or plan should be produced so the installer knows the type of AFD and where it should be fitted.

Category M systems should have manual call points (MCPs) at each final exit to the open air and at each storey exit near stairs, with sounders throughout the building, but no AFD. For Category L5, M is not included as standard, so if if MCP are required, then this needs to be made clear: L5/M.

Speciﬁers’ Guide

Section 1

Selecting the correct category of system and choosing the system technology

There are two different property protection categories.

Section 1

Category P1 systems should have AFD throughout the building covering all rooms and areas. A means of contacting the fire and rescue service (F&RS) would need to be included. This could be automatic transmission equipment or 24 hour cover by security personnel who could telephone the F&RS.

Category P2 systems would have AFD installed only in defined parts of the building, sometimes as specified by the insurers, again with a means of contacting the F&RS.

For categories P1 and P2, M is not included as standard, so if MCPs are required, then this needs to be made clear: P1/M; or P2/M.

Examples of categories of system that might be appropriate to particular buildings would be3: Hotels

L1 or L2

Hospitals (refer to HTM 05-03 Part B)

L1 (with possible variations)

Offices

Large offices, high value

M/P1 or M/P2

Shopping complexes

Factories/warehouses

M/P1 or M/P2

For both category L2 and category P2 systems, it will be necessary for someone to define the areas in which detectors are to be installed. This should normally be the purchaser, but if you are the designer you are responsible for this, you should ensure that the areas selected are agreed by the interested parties. Reference to other standards and codes may be required in order to define these areas4. For example, for a category L2 system, it would be relatively simple to make a list of boiler rooms, kitchens, plant rooms etc, to be protected in addition to a category L3 system, but less obvious could be day-lounges where people could be asleep.

3 Examples of appropriate categories of system for typical premises are given in Annex A of BS 5839-1. 4 See page 90 of this guide

Section 1

Selecting the correct category of system and choosing the system technology

Where, in any category 1 system, there is a need to protect a room or area, voids deeper than 800mm within the room or area would, in general, need to be protected (Fig 3a). For example a category L4 would be protected with smoke detectors located in the escape route corridors and stairways. A void deeper than 800mm above the escape route would need to be protected with fire detection, but a void elsewhere would not need protection. However, if a void bridges across the escape route and other areas then the whole of that void would need fire detectors, see figure 3b and 3c.

Section 1

Speciﬁers’ Guide

> 800mm

Fig 3a Voids deeper than 800mm generally need to be protected

Detectors not required in the rooms, nor in the voids above the rooms

Roo m

Esc ap Rou e te

Roo m

Detectors recommended in escape routes and in void immediately above only

Fig 3b Voids above rooms

> 800mm

Speciﬁers’ Guide

Section 1

Selecting the correct category of system and choosing the system technology

Detectors throughout the void

Section 1

Roo m

det e req ctors uire not d fo r L4

Esc ap Rou e te

Roo m

det e req ctors uire not d fo r L4

> 800mm

Detectors recommended in escape routes and in voids if a ﬁre could spread from one area to threaten the escape route

Fig 3c Voids bridging an escape route

Where only part of the building is protected by AFD, account should be taken of the potential for a fire to start in an unprotected area and spread to the area covered by detectors. In category P2 systems, there should normally be fire resistant construction separating the protected from the unprotected areas, but there is no guidance on what standard of fire resistance would be appropriate for this construction. The insurers may require a 1 hour fire resistant construction, or otherwise category P1 may be necessary. The insurer should be consulted for advice on property protection. Remember that BS 5839-1 does not recommend which category of system should be used in any particular building. It would be part of the risk assessment procedure to determine the appropriate category. 18

Establishing the category of system is a key step in the design process. This will determine the areas in which automatic fire detection will need to be provided. It also has implications for detector choice, siting and spacing5.

Proposing the system category BS 5839-1 states that the specifier or purchaser should ideally specify the category of the system required, but it goes on to state that in the absence of the category being specified, the fire alarm designer may propose a category. While it may not be the designer’s job to specify the category, it will expedite the work if some assistance is given to the owner or manager of the premises. However, in this case, the category designed should be made clear to the purchaser, so that he can seek professional advice from a fire safety specialist (if he wishes) regarding the suitability of the category for the premises in question.

5 See page 41 of this guide (LOCATION AND COVERAGE OF DETECTORS)

Section 1

Selecting the correct category of system and choosing the system technology

Section 1

Speciﬁers’ Guide

L4 L3 L2 L1 Fig 4 Typical areas covered by AFD in L Categories

The examples below show how decisions could be made on choosing the category of fire protection: • Category M. An office building divided into a number of rooms with people occupying most rooms, or circulating between rooms regularly. If a fire were to start someone would quickly be aware of it and could operate a manual call point (MCP). With alarms throughout the building, all the other occupants would quickly be warned and they would then be able to evacuate. • Category L4. A larger single or multi-storey building with more than one escape route, with many unoccupied areas and good fire resistant construction with self-closing fire doors to limit fire spread. Optical smoke detectors would be fitted on all escape route corridors and stairways so that if a fire were to start the occupants would be warned when it reached one of the escape routes. Even if an escape route became blocked by smoke, people would be able to escape by an alternative route. • Category L3. A building with a number of unoccupied rooms, or a number of different tenants and perhaps with only one escape route (e.g. one stairway). In this case, with fire detectors (not necessarily smoke detectors) in all rooms opening onto the escape route(s), a fire would be detected and the sounders would operate before smoke reached the escape routes, enabling people to evacuate, possibly walking past the door to the room of fire origin. This would offer a better standard of detection than category L4, because a fire would quickly be detected, in the room of origin, rather than waiting until smoke reached the smoke detectors in the escape route. • Category L2. A similar building to the category L3 above but with higher risk rooms such as boiler rooms, plant rooms, kitchens etc. These rooms would be separately listed and protected with appropriate fire detectors, even if they did not open onto an escape route. This category is usually appropriate for hotels. • Category L1. Sleeping accommodation such as a hotel or care home, where the intention is to protect the lives of all the occupants. Smoke detectors in all bedrooms and day rooms would protect the occupants, so that if a fire started they would be woken by the alarms and could evacuate, or be assisted to evacuate. Non-bedrooms (where no-one would be asleep) would be protected with a detector to suit the risk, such as a heat detector in a kitchen.

Speciﬁers’ Guide

Section 1

Selecting the correct category of system and choosing the system technology

Section 1

• Category P1. A valuable building or valuable contents, of any size or design, that the insurers or owners would not want extensively damaged. In this case category P1 would be appropriate. With detectors in all rooms and areas where a fire could start, it would be detected within a few minutes. The fire & rescue service (F&RS) could then be contacted either by on-site personnel (e.g. security), or by using a radio and/or telephone land line link to an Alarm Receiving Centre (ARC). The ARC then contacts the F&RS. Sounders would only be required to alert staff. The likelihood is that the building would be occupied at some time of the day, in which case the appropriate category would be M/P1. For a small unmanned building, only occasionally visited by one or perhaps two building engineers, MCPs would not normally be necessary, unless their working procedures were to disable the AFD whilst working to avoid false alarms and if a fire started, or if the engineers accidentally started a fire, to operate an MCP and so send a signal immediately to the ARC. Prescriptive categories. All the above categories L4, L3, L2, L1, P1 may be regarded as prescriptive categories because the recommendations for each are clearly specified in BS 5839-1. For strict accuracy, the high risk parts of category L2 would be listed separately and therefore those parts could be regarded as nonprescriptive. Non-prescriptive categories. The categories P2 and L5 shown below may be regarded as non-prescriptive categories because there is no unique specification for the areas that need to be protected, these are selected on the basis of risk. • Category P2. A partly valuable building or contents where the insurers or owner identify certain areas for protection. Normally there would be fire resistant construction separating the protected area(s). • Simple category L5. A building that would not need AFD, other than for just one area, such as a boiler room, where a heat detector would be installed to operate the sounders, allowing people to escape before the fire threatened their escape route. This one detector, with sounders throughout the building would constitute a simple category L5 system. Normally the fire alarm system designer would be able to take on the responsibility for this decision and proceed with the design. • Complex category L5. A more complex building for which someone has carried out a full fire risk assessment could be the subject of a fire engineered solution, taking into account constructional and procedural details. A category L5 system could be part of this solution with the extent of protection, siting of detectors and plans to specify the system given to the fire alarm system designer. It can be seen that this work would require considerable skill and time involving many fire safety disciplines. Information on the areas to be protected should always be given to the fire alarm system designer.

• Categories X/M. BS 5839-1 specifies MCPs as prescriptive recommendations in categories L1, L2, L3, L4, but if, for categories P1, P2 or L5, MCPs were required, then the category becomes M/P1, M/P2 or M/L5.

Speciﬁers’ Guide

Section 1

Selecting the correct category of system and choosing the system technology

Fire detection systems are available as non-addressable (also known as “conventional” systems) or as analogue addressable. There is no definitive size or type of building that would be suitable for analogue addressable rather than non-addressable systems. Often the benefits of the analogue addressable will bias the choice towards this technology, but for buildings with only a few zones a non-addressable system would meet the recommendations of BS 5839-1 and provide perfectly adequate fire detection.

Non-addressable systems

Section 1

System technology

Non-addressable detectors and MCPs are usually connected in parallel across a two-wire radial circuit and terminated at an end-of-line device (EOL). The EOL provides monitoring of open and short circuit faults at the fire alarm control panel. Each detector is a two-state device capable of indicating one of two states - normal (non-fire), or alarm (fire). Each circuit would constitute a zone of the system6 and would therefore be wired so as to connect the detectors in the area covered by that zone7. The control panel can then indicate if there is an open or short circuit fault on any zone, or if a fire has been detected or an MCP operated in a zone. Non-addressable systems are widely available and provide an economic and perfectly satisfactory means of fire detection in many small to medium-sized buildings (Fig 5a).

ZONE 1

ZONE 2

ZONE 3

Conventional Detector

Fig 5a Circuit arrangement on a conventional system

6 See page 24 of this guide (SYSTEM ZONE CONFIGURATION) 7 See page 28 of this guide

Manual Call Point

Addressable Sounder

End of Line device

Speciﬁers’ Guide

Section 1

Selecting the correct category of system and choosing the system technology

ZONE 1

Section 1

ZONE 2

ZONE 3

Analogue Addressable Detector

Addressable Manual Call Point

Addressable Sounder

Fig 5b Circuit arrangement on an analogue addressable system

Analogue addressable systems In analogue addressable systems, detector circuits act as data communication highways that allow detectors to communicate much more information about their status to the control panel, using digital signalling techniques (Fig 5b). In contrast with a conventional system, the control panel can display the address, showing which detector or MCP has been activated and a description of its exact location, level, room etc., and also whether more than one device has activated on the same circuit. Multiple detector activations and MCP operations during the spread of a fire could then be observed and dealt with more effectively. The control panel for analogue addressable systems usually has an on-board printer so that past events can be printed out and appropriate action taken, and if necessary any false alarms dealt with. Because an addressable system provides the exact location of any fire that is automatically detected, it enables more rapid action to be taken to deal with the fire and ensure the occupants in this vicinity are evacuated. This can for, example, be important in a care home, in which some time that is needed to assist residents with evacuation can be lost in searching for a fire if a conventional system is installed.

The analogue signal represents the level of the phenomenon sensed (e.g. heat, smoke, etc) at that detector and this can be processed and used to select day/night settings, for example to make detectors more sensitive out of working hours to give faster protection for property (while maintaining EN 54 compliance). Some designs of analogue addressable systems can sense the difference between a very slow build up of contamination and a fast changing signal due to a genuine fire. This also helps to reduce false alarms. Service and maintenance can also be improved using analogue addressable systems, because any contamination in the detector can be displayed or printed out and the detector replaced if necessary, to ensure correct operation and reduce false alarms. Analogue addressable systems are more sophisticated than conventional systems and in the past they tended to be used only in large buildings. However, they are now in more widespread use and can often be as economically viable in small to medium-sized buildings as conventional systems. In order to maximise the potential benefits in terms of false alarm reduction, BS 5839-1 recommends that systems incorporating a large number of detectors (more than 100 is given as an example) should be of the analogue addressable type.

Speciﬁers’ Guide

Section 1

Selecting the correct category of system and choosing the system technology

Fire alarm control panels, in conjunction with analogue addressable detectors can have a certain amount of intelligence. As an example, this can be used for drift compensation, so that if a detector slowly becomes affected by contamination, the control panel adjusts for this, within certain limits, and the resultant sensitivity to fire remains unaffected. This can also be read via the control panel for service levels. Some intelligence, such as drift compensation, can be built into the detector rather than the control panel, the terminology for this being “distributed intelligence” (see Fig 6). Sensitivity modes can also be set from the control panel at commissioning, to select the most suitable speed of detection, according to the application in the area, and avoid false alarms. The Apollo Discovery range of detectors includes distributed intelligence with high sensitivity mode 1 to lower sensitivity mode 5, all modes being within the relevant EN 54 standard.

Section 1

Intelligent systems

COMPENSATION IN ACTION

Alarm threshold

Raw analogue value

Compensated analogue value

COMPENSATION LIMIT Limit of compensation Alarm threshold

Raw analogue value

Compensated analogue value

NORMALISATION

Alarm threshold Raw analogue value

Compensated analogue value

Fig 6 Drift diagrams

Speciﬁers’ Guide

Section 1

System zone conﬁguration

1.3 SYSTEM ZONE CONFIGURATION Section 1

Zoning is necessary in order to provide suitable indication of the area of the building in which a detector has operated or a manual call point has been activated. Such zones are referred to as ‘detection zones’. However, particularly in buildings in which evacuation is phased, or it is intended to operate a two stage alarm arrangement, the term ‘zone’ may also be used to describe an area in which either the ‘Evacuate’ signal or the ‘Alert’ signal is given8. These zones are referred to as ‘alarm zones’.

Detection zones The process of configuring the detection zones involves sub-dividing the building into a number of separate areas which are sufficiently small and which relate to the layout of the building so as to provide an unambiguous indication of the location of the fire. A zone plan should be installed near the control panel so that the zonal indication can be related to the location in the building. The zone plan should show the basic building layout, the zones, all the escape routes, circulation areas, and all entrances. The intention is to assist those responding to a fire, such as the F&RS by reducing the search time to locate a fire and helping to identify the source of a fire quickly. It should be noted that BS 58 39-1 recommends that this plan should always be provided. A simple list of zones does not comply with the British Standards. Detection zones should be determined on the following basis9: • Zone floor area is 2000sq m maximum (see Figure 7a) • Except in the case of small buildings (those with a total floor area of 300sq m or less), no zone should cover more than one storey. For the avoidance of doubt, multi-storey zones are not permitted (except as above), even if each floor is substantially less than 2000sq m, see Figure 7b.

ZON E7

ZON E4 ZON E1

Each storey, for example 4500sq m would need to be split into 3 zones

ZON E5 ZON E2

ZON E6 ZON E3

Fig 7a Large storeys need to be split into zones

8 See page 54 of this guide (AUDIBLE AND VISUAL ALARM REQUIREMENTS) 9 The criteria for determining zoning are given in clause 13 and 14 of BS 5839-1.

ZO NE 8

Section 1

System zone conﬁguration

Section 1

Speciﬁers’ Guide

ZON E3

ZON E2

ZON E4

ZON E1

ZON E5

ZON E4 ZON E3

ZON E6

ZON E2 ZON E1

Fig 7b Zones are restricted to one storey, even if substantially less than 2000sq m

Speciﬁers’ Guide

Section 1

System zone conﬁguration

• The ‘search distance’, the distance that needs to be travelled after entering the zone in order to determine visually where the fire is, should not exceed 60m for non-addressable systems (Fig 7c).

Section 1 60m MAX

Fig 7c Search distance for a ﬁre should be no more than 60m in a zone

• Any enclosed flue or chimney-like structures, such as stairways and lift shafts, should be separate zones, see Figure 7d. Lift shaft (ZONE 7) Hoist (ZONE 8)

ZON E5

ZON E4 ZON E3

ZON E2 ZON E1

Each storey is less than 2000sq m

Fig 7d Stairways and lift shafts are separate zones

ZO NE 6

Speciﬁers’ Guide

Section 1

System zone conﬁguration

• In multi-storey buildings the MCPs near the storey exit should display fire on the associated storey zone. This applies whether the MCP is sited within the stairway landing or in the accommodation area

• Where an MCP is sited in a stairway near a final exit to open air at the bottom of the stairs, then that MCP may either be incorporated in the stairway zone (see Figure 7e), or it can be incorporated within the zone that serves the floor on which the exit is located (e.g. the ground floor selection zone).

Section 1

(e.g. corridor or office).

ZO NE 5 Z4

ZON E4

ZON E3

ZON E2

ZO NE 6 Z3

ZON E1 MCPs located on the stairway, conﬁgured or wired to show at the control panel in the associated storey zone

Z6 Z1

Fig 7e MCPs on stairways show ﬁres in related zones

Similar zoning criteria apply to systems comprising only manual call points (category M), but for an open area such as a large warehouse, someone may see a fire and travel some distance before operating an MCP. In this case the 2000sq m zone size limitation can be increased to 10,000sq m. If the warehouse also has AFD then it would be necessary to assign 2000sq m areas for the AFD, superimposed over the MCP zone. For example, for a 10,000sq m warehouse, one zone could be assigned to the MCPs and five zones assigned to the AFD, making 6 zones total.

Speciﬁers’ Guide

Section 1

System zone conﬁguration

Section 1

66m

AFD Z2

AFD Z3

AFD Z4

AFD Z5

AFD Z6

150m Fig 8 AFD zones superimposed on an MCP zone

These zoning criteria apply to both analogue addressable and non-addressable (conventional) systems, the 60m search distance being the exception that applies only to non addressable systems.

Alarm zones Alarm zones may be required in a building with: • a staged alarm (e.g. where areas threatened by fire would have the full evacuate signal, but areas remote from the fire may have an alert pulsing signal, often one second on, one second off); or • a phased evacuation system where, for example, the building is evacuated typically two floors at a time, starting with the floor of activation, and the floor immediately above. The operation of alarm zones would be documented in a cause and effect sequence, programmed into the control panel and fully tested by the commissioning engineer. The boundaries of alarm zones should comprise fire resisting construction (unless they are external walls). While an alarm zone can incorporate more than one detection zone, a detection zone cannot cover more than one alarm zone. Boundaries of alarm zones should coincide with boundaries of relevant detection 28

zones (Figs 7a, 7b and 7d). There is no area or size limitation for alarm zones given in BS 5839-1.

Section 1

System zone conﬁguration

Section 1

Speciﬁers’ Guide

Detection ZONE 1

Detection ZONE 2

Detection ZONE 3

Fig 9a Alarm zone containing 3 detection zones

All in one detection zone

Fig 9b Alarm zone containing just one detection zone

Speciﬁers’ Guide

Section 1

System zone conﬁguration

Non-addressable zones versus analogue addressable zones The time taken to locate a fire would clearly be reduced if its exact location were known. An advantage of the analogue system is that the exact location is displayed at the control panel, whereas in a conventional

Section 1

system, the indication only narrows the location down to “somewhere in that zone”, which could be as large as 2000sq m (or within the 60m search distance). The 60m maximum search distance recommended applies to non-addressable systems, but for analogue addressable systems, provided that the text description of the location of the activation is clearly displayed and can be readily interpreted by those unfamiliar with the building without any manual operation of controls on the control panel, the search distance criterion does not apply. In some buildings, with complex search routes, the resulting non-addressable zones may have to be much less than 2000sq m, because of the limitation imposed by the 60m search distance. In the same building with an analogue addressable system, the zones could be the full 2000sq m area. The importance of establishing the zoning of a system at an early stage in the design cannot be over emphasised. With a conventional non-addressable system, each zone corresponds to a separate circuit. Re-configuring the zoning at a later stage can therefore result in costly wiring changes. Detection zoning on an analogue addressable system is a function of software, and a single circuit, usually in the form of a loop with detectors, MCPs etc., will often have several zones. Changes at a later stage in a project can therefore be more readily accommodated. However, alarm zones sometimes comprise discrete circuits of sounders and re-configuring of these zones can also involve costly wiring changes. Note that different criteria govern circuit design in analogue addressable systems10.

Visual indicators on detectors The visual indicators on detectors should be orientated to be readily seen by a person entering the room where the detector is located. This may be less important where detectors have two indicators.

Remote visual indicators Remote visual indicators can be particularly useful for showing if a fire is located in a void or a locked room. Wiring should be of the same fire resistant type as the detection circuit. However, the wiring to remote visual indicators is not normally monitored and it is good working practice to limit the cable run from detector to indicator to just a few metres. The operation of the indicator should be checked annually with the associated detector. 30

BS 5839-1 does not actually state in any recommendation that remote indicators should be fitted, but it does mention in the commentary that they would be advisable, especially for non-addressable systems. It is therefore good working practice to allow for remote indicators, where necessary, and it is worth reading the job specifications carefully because some state that for voids remote visual indicators be fitted as part of the contract.

10 See page 65 of this guide (CIRCUIT DESIGN)

Section 1

System zone conﬁguration

Corridor

Remote visual indicator

Smoke detector with LED

Same cable as detection circuit

Typical Room

Section 1

Speciﬁers’ Guide

Locked Room

Fig 10a Visual and remote indicators

Protected Void

Remote visual indicator

Protected Area

Fig 10b Remote visual indicator for a void 31

Speciﬁers’ Guide

Section 1

Selecting the correct detectors

1.4 SELECTING THE CORRECT DETECTORS Section 1

Types of fire detector (BS 5839 pt1 Clause 21) Fire detectors are designed to detect one or more of the four key characteristics of fire: • Smoke • Heat • Infra-red or ultra-violet radiation (flames) • Combustion gas (e.g. carbon monoxide). The most widely used detectors are those that respond to either smoke or heat. Flame detectors that look for infra-red, ultra-violet or combined infra-red and ultra-violet radiation tend to be used for more specialist applications and, in particular, where a fire involving flammable liquids (such as alcohol) is expected. Combustion gas detectors, in particular carbon monoxide (CO) fire detectors, respond well to slow, smouldering fires and may be advantageous when used to protect bedrooms. Slow burning fire such as most bedding fires produce CO gas as a product of combustion, whereas fast burning flaming fires produce carbon dioxide (CO2) with the smoke and other products of combustion. CO detectors are useful in avoiding certain false alarms. For example, if a resident, in a hotel bedroom with en suite shower room, leaves the shower room door open, a smoke detector may see the shower “steam” as smoke and be activated, giving rise to a false alarm. But with a CO detector, even if it is fitted near to the shower room door, a false alarm due to “steam” would be avoided. CO detectors therefore have applications in areas where smoke detectors would produce false alarms, but where heat detectors would be too slow to operate. Multisensor detectors contain more than one sensor within the same detector. They are able to monitor more than one of the characteristic phenomena of fire (for example, heat and smoke). Use of these detectors can potentially result in a significant reduction in false alarms. Detectors can be either ‘point’ type, where the relevant characteristic of fire is detected at a defined point within the protected area, or ‘line’ type, where the detector senses along a defined line in the protected area. Most smoke detectors that are used are of the point type, and these are satisfactory

for most applications. However, optical beam smoke detectors are available, which are effectively line type smoke detectors. These can be particularly beneficial and cost effective in certain applications, for example, large open spaces with high ceilings (e.g. warehouses) or where access for maintenance of point detectors would present difficulties. Aspirating smoke detectors are also available, in which samples of air are drawn, by a pump or fan, through holes in pipework within the protected area, to a central detector. The sensor within the detector usually operates by means of optical principles. These often utilise sensors of very high sensitivity, and are thus particularly beneficial in the clean environment of a computer room, where any smoke is diluted by the rapid air movement within the room. However, they are also used:

Speciﬁers’ Guide

Section 1

Selecting the correct detectors

• For reasons of aesthetics, the pipework could be concealed above a ceiling with capillary tubes to small sampling points through which samples of air are drawn, this being the only visible part. sample holes once installed do not always require attention during routine servicing and can often be cleaned using vacuum techniques without needing access to the pipework in the protected area. • Where the temperature inside the room is too low for point detectors, for example in cold stores, where the aspirating detector can be located outside the room.

Section 1

• Where access for maintenance may be difficult, such as for high ceilings or in some voids. Pipework and

Heat detectors can also take the form of either point type or line type detectors and are designed to either respond when a fixed temperature is reached (fixed temperature heat detectors) or when the rate of change of temperature within the room is abnormal (rate-of-rise heat detectors11). In the case of the latter the heat detector should still respond when the fixed temperature limit is reached.

Choosing the right detector No one type of detector will be suitable for all applications. The choice of detector will largely be governed by three key considerations: • The nature of the fire hazard. • The speed of response required. • The need to minimise false alarms. Other factors such as cost, suitability for the working environment and ease of maintenance will also need to be considered.

Smoke detectors Smoke detectors respond quickly to most fires and generally much faster than heat detectors. They are usually the first choice in most applications, unless false alarms would be a problem or the fire load would not give off smoke (for example in an alcohol bottling plant). Smoke detectors work on one of two principles: 1. Ionisation smoke detectors. The sensing part of the detectors consists of two chambers - an open, outer chamber and a semi-sealed reference chamber within. Mounted in the reference chamber is a low activity radioactive foil of Americium 241, which enables current to flow between the inner and outer chambers when the detector is powered up. As smoke enters the detector, ions become attached to the particles, causing a reduction in current flow in the outer chamber and hence an increase in voltage measured at the junction between the two chambers. The voltage increase is monitored by the electronic circuitry, which triggers the detector into the alarm state at a pre-set threshold. An externally visible red LED lights up when the detector changes to alarm state. Ionisation chamber smoke detectors respond well to small particles. These are usually found in the smoke from fast burning fires. Use these detectors particularly where rapid, open flaming fires are likely. However, although modern ionisation detectors have an extremely low level of active material, they are subject to the Ionising Radiation Regulations, which control storage, transport and disposal. Consequently they tend to be used for protecting particular risks, where other detectors would not be suitable. Integrating ionisation smoke detectors work on the same principle as the ionisation smoke detector, but has modified signal processing circuitry, which allows an alarm threshold to be present for up to 20 seconds without initiating an alarm. This type of detector is suitable for use in areas where transient high levels of smoke – like pollutants – may be expected. 11 Rate-of-rise heat detectors also respond when a ﬁxed temperature is reached

Speciﬁers’ Guide

Section 1

Selecting the correct detectors

10 volts on foil holder

Section 1

Radioactive foil Reference chamber Sensing electrodes Sensing chamber 0 volts

In clean air Positively charged ion

With smoke Negatively charged ion

Smoke particle

Fig 11 Ionisation smoke chamber

2. Optical detectors utilise a small light source and a light sensor in a chamber that excludes external light. In clean air conditions, the light sensor is arranged to receive little or no light from the source. If smoke particles enter the chamber the light is scattered, some falls on the sensor and the signal from this is processed to sense fire. However, smoke detectors are also more likely to give rise to false alarms than other types of detector. They may not therefore be suitable in kitchens or workshops where steam, cooking fumes or dust would be in the normal environment. Although ionisation chamber and optical smoke detectors have a wide range of response, there are differences in sensitivity between the two types. This may make one type more suitable than the other for your application. 34

Optical smoke detectors respond well to visible smoke. If you can see the smoke, the optical detector will detect it. Optically dense smoke is formed with large particles, such as smoke that has aged before it reaches the detector. An example of aged smoke would be where a fire has started in a room opening onto an escape route and the smoke has travelled a long way, or “aged” in passing through any gap around the door, on its way to the smoke detector in the escape route. In the ageing process, the smaller particles of smoke merge together to make larger more visible particles. For this reason BS 5839-1 recommends the use of optical smoke detection for escape route corridors and stairways. It is important to remember that most fires are mixed and produce both large and small particles of smoke and an optical smoke detector is most likely to detect the fire.

Speciﬁers’ Guide

Section 1

Selecting the correct detectors

Section 1

Photo-diode

Infra-red LED

In clean air Light beam

With smoke Diffused light beam

Smoke particle

Fig 12 Optical smoke chamber

It should be understood that whether a smoke detector takes two seconds or two minutes to detect a fire, it is not normally critical in the initial stages of a fire, because fire doors and fire resistant construction should contain the fire long enough for people to escape to a place of safety.

Heat detectors Heat detectors are generally less sensitive to most fires than other types of fire detector, although they may detect the heat from certain clean burning fires. For fires involving flammable liquids such as alcohol (which produce very little smoke), a heat detector would operate before a smoke or CO detector. In a category L3 system, although smoke detectors in rooms opening onto escape routes would give the earliest response, BS 5839-1 permits the use of heat detectors. The objective is to give warning, while the fire is still restricted to the room of origin, before the escape route becomes impassable for the other occupants. In these situations, a heat detector has been found to respond fast enough12. Heat detectors are unlikely to respond to smouldering fires. This lack of sensitivity to certain fires will make them unsuitable for situations where warning of the presence of smoke is required or where unacceptable damage would result from a small fire. However, heat detectors can often withstand environmental conditions that would adversely affect other types of detector or give rise to false alarms. They also require little maintenance. Rate of rise heat detectors would be used in, for example, a kitchenette with microwave, kettle and toaster, where smoke detectors may give rise to false alarms. Fixed temperature heat detectors would be used in a kitchen or boiler room, where smoke detectors and also rate of rise detectors would give rise to false alarms. Line type heat detectors can be used with analogue addressable and conventional systems, using suitable interfaces for the fixed temperature and rate of rise technologies.

12 Heat detectors may not be suitable for all adjoining rooms. Smoke detectors should always be provided if the room is a dormitory with several people sleeping or is a bedroom used by disabled people.

Speciﬁers’ Guide

Section 1

Selecting the correct detectors

Dual thermistor heat detection Normal conditions

Rate-of-rise response

Fixed temperature response

Section 1 Thermistor partially sealed from surrounding air

Thermistor exposed to air

Fire detected on fast increase of ambient temperature

Fire detected on slow increase of ambient temperature

Note: Analogue addressable heat detectors use only a single thermistor

Fig 13a Dual Thermistor Heat Detection

Address buttons

Thermistor bead

Case moulding

PCB

Lid moulding

LED

LED Heat shrink sleeving

Fig 13b Single Thermistor

Speciﬁers’ Guide

Section 1

Selecting the correct detectors

Flame detectors Unlike smoke and heat detectors, flame detectors do not rely on convection currents to transport the fire combustion. They provide a very fast response to fires involving flammable liquids or gases, and will often be the most suitable type in these applications. They can be used to protect very large open areas without reducing the speed of response, where other types of detector would not be effective. To ensure that full coverage is maintained, flame detectors require a clear line of sight within the area to be protected.

Section 1

products to the detector. Flame detectors are designed to sense the radiation emitted by flames during

Height

Length

Width

Fig 14 Flame detectors require clear line of sight

Carbon monoxide (CO) fire detectors CO fire detectors are immune to many of the environmental influences that would cause false alarms with smoke detectors, such as dust, steam and cigarette smoke. They respond well to smouldering fires, where there is incomplete combustion, but they will not respond early enough to fast, free-burning flaming fires, which have sufficient oxygen for complete combustion, producing CO2 (rather than CO). Care is needed to ensure that CO fire detectors are suitable for their intended application.

Speciﬁers’ Guide

Section 1

Selecting the correct detectors

Filter

Section 1

Sensing electrode

Wick (contains electrolyte)

Counter electrode

In clean air

With CO Sensing Counter

2CO2 + 4H+ + 4e2H20

2CO + 2H20 4H+ + 4e- + O2

Fig 15 Carbon monoxide ﬁre detectors

Multisensor detectors The combination of different principles of detection in a multisensor detector means that the overall performance of the detector in responding to different fires is enhanced. It also introduces the potential to significantly reduce false alarms. A combined optical/heat multisensor detector has been found to respond well not only to smouldering fires, but also to the fast burning fires favoured by ionisation smoke detectors. At the same time, it is possible to reduce the sensitivity of the detector to the sources of false alarms, such as steam, that normally affect optical smoke detectors Photo-diode

Infra-red LED

Fig 16 Multisensor detector

Thermistor exposed to air

Speciﬁers’ Guide

Section 1

Selecting the correct detectors

General detector choices Whether a detector will respond quickly enough depends on whether the response will satisfy the fire so as to provide sufficient early warning; heat detectors would be unsuitable for this purpose. Smoke detectors are preferred for property protection, but this will depend on whether false alarms that might result from the normal environmental conditions in the protected area can be avoided. In selecting the detector, the designer must take account of the environment to which the detector will

Section 1

safety objective for the system. Smoke detectors must be used in escape routes for life safety systems

be exposed and the potential for false alarms. There are many ways of managing the false alarm issue and these are discussed later13. However, the most fundamental step the designer can take is to make the correct choice of detector. The relative sensitivity for Apollo detectors is shown in figure 17.

OPTICAL

IONISATION

SENSITIVITY

MULTISENSOR

HEAT OVERHEATING

SMOULDERING

GLOWING

FLAMING - EARLY

FLAMING - LATE

Fig 17 Relative detector sensitivity

An example of a growing fire is shown by the orange shaded portion and lines show the possible sensitivity of the various detectors.

13 See page 76 of this guide (FALSE ALARMS)

Speciﬁers’ Guide

Section 1

Selecting the correct detectors

Relative performance of detectors in test fires

Section 1 40

Optical

Multisensor

Ionisation

CO/Heat

Heat

Overheating/thermal decomposition

Very good

Poor

Very poor

Smouldering/glowing combustion

Very good

Moderate/ good

Excellent

Very poor

Flaming combustion

Good

Very good

Moderate

Poor

Flaming with high heat output

Good

Very good

Poor

Moderate/ good

Flaming clean burning

Very poor

Moderate/ good

Poor

Moderate/ good

Very poor

Moderate/ good

Speciﬁers’ Guide

Section 1

Location and coverage of detectors

Heat and smoke from a fire will rise and collect at the highest point in the room. It is there that heat and smoke detectors should be sited. However, as smoke and hot gases rise from the fire, they become

Section 1

1.5 LOCATION AND COVERAGE OF DETECTORS

diluted with cool, clean air. As a result, the size of fire required to operate smoke and heat detectors increases as the height of the ceiling above the fire increases. The use of more sensitive detectors can, to some extent, counter this effect, but it is still necessary to limit the height at which detectors can be installed. Optical beam smoke detectors are less sensitive to this effect than point detectors, and, as a result, they can be used at greater heights. BS 5839-1 gives the maximum height for mounting detectors14 as: Heat detector, rate of rise

9m (13.5m)

Heat detector, fixed temperature

7.5m (12m)

Point smoke detector

10.5m (15m)

Point CO fire detector

10.5m (15m)

Optical beam smoke detector

25m (40m)

Figures in brackets apply to category P systems if there is a “rapid response” fire brigade attendance time of not more than five minutes from being called. It is possible, particularly in rooms with high ceilings, for smoke to cool to such an extent that it stops rising before reaching the ceiling. This is known as stratification. The smoke may form a layer a few metres below the ceiling and, as a result, ceiling mounted detectors may not operate. It is difficult, in practice, to predict where stratification will occur, because it may be caused by time related effects such as the sun shining on the roof, or overhead heaters causing a build up of heat. Eventually, as the fire grows, the smoke will have sufficient buoyancy to overcome and break through any stratification to reach the ceiling and thereby operate the ceiling mounted detectors. As a result, it is always necessary to mount detectors on ceilings, even if additional detectors are also mounted below. Alternative techniques for consideration could be to use a number of vertical aspirating pipes in addition to horizontal pipes near the ceiling, or point detectors on the ceiling. When locating detectors, the designer should take account of the following: • Detectors should be positioned at the highest part of the protected area, though additional detectors may be lower than this (see earlier comments on stratification). • Detectors should not be sited more than 150mm below the ceiling in the case of heat detectors (Fig 19a), and no more than 600mm in the case of smoke detectors (Fig 19b).

14 Limit on the heights of ceilings are given in Tables 3 and 4 of BS 5839-1.

Speciﬁers’ Guide

Section 1

Location and coverage of detectors

Section 1

150mm

Thermistor

HEAT DETECTOR Fig 19a Heat detectors must not be sited more than 150mm below the ceiling

600mm

Optical chamber

SMOKE DETECTOR Fig 19b Smoke detectors must not be sited more than 600mm below the ceiling

• For vertical chimney-like or flue like shafts (e.g. lift shafts or open risers) a detector should be located in the shaft, at the top, and also, in the accommodation area within about 1.5m, at each level where there is a door or access hatch to the shaft (e.g. lift doors) (see Fig 20).

LIFT SHAFT

1.5m

Fig 20 Detectors should be located within 1.5m of vertical shafts

Speciﬁers’ Guide

Section 1

Location and coverage of detectors

• Detectors should not be mounted closer than 500mm to any walls or ceiling beams (over 250mm deep) (Fig 21). • If a partition or storage rack reaches to within 300mm of the ceiling, treat it like a wall dividing the

BEAM

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room in two and provide a detector each side (Fig 21).

Apollo Fire Alarm Design Guide PDF - PDFCOFFEE.COM (2024)

References