BS5839–1 and NFPA72 – A Overview
Scope of BS 5839-1 and NFPA 72
In ensuring that reasonable care and due diligence have been taken in the design of fire detection and alarm system, compliance to technical standards is a key test. Two standards of which Malaysian engineers are most familiar are BS5839 and NFPA 72.
BS5839 "Fire Detection and Alarm Systems for Building" comprise 8 parts. British Standards (similar to ISO standards) are structured into parts with each part containing particular aspect of the standard or code. Each part is self-contained within its own right and as can be seen from a listing of all parts of BS5839, Part 1 "code of practice for system design, installation, commissioning and maintenance" will be the code consulted by design engineers.
* Part 1-:-2002 – Code of practice for system design, installation, commissioning and maintenance.
* Part 2-:-1983 – Specification for manual call points (withdrawn and replaced by BS EN54-11:2002)
* Part 3-:-1988 – Specification for automatic release mechanisms for certain fire protection equipment
* Part 4-:-1988 – Specification for control and indicating equipment (withdrawn and replaced by BS EN54-2 'Control and indicating equipment' and BS EN54-4 'Power supply equipment').
* Part 5-:-1988 – Specification for optical beam smoke detectors.
* Part 6-:-1995 – Code of practice for the design and installation of fire detection and alarm systems in dwellings.
* Part 8-:-1998 – Code of practice for the design, installation and servicing of voice alarm system.
* Part 9-:-2003 – Code of practice for the design, installation, commissioning and maintenance of emergency voice communication systems.
NFPA 72 "National Fire Alarm Code" published by the National Fire Protection Association of North America, in contrast to BS5839 is published as one self-contained book (as is the normal structure of NFPA standards). NFPA72 is styled as a manual but worded as a legal document. It is organised into chapters with 'Articles' within each chapter. The 2002 edition reorganised the chapters of the previous (1999) edition as follows:
* Chapter 1 – Scope and purpose;
* Chapter-2-–-Referenced publications (previously chapter 9);
* Chapter-3 – Definitions (previously contained in chapter 1);
* Chapter-4-– Fundamentals of Fire Alarm Systems (previously contained in chapter 1);
* Chapter-5-– Initiating devices (previously chapter 2);
* Chapter-6-– Protected premises fire alarm systems (previously chapter 3);
* Chapter-7-– Notification appliances for fire alarm systems (previously chapter 4);
* Chapter-8-– Supervising station fire alarm systems (previously chapter 5);
* Chapter-9-– Public Fire Alarm Reporting Systems (previously chapter 6);
* Chapter-10-– Inspection, testing, and maintenance (previously chapter 7);
* Chapter-11-– Single- and multiple-station alarms and household fire alarm systems (previously titled 'Fire warning equipment for dwelling units in chapter 8).
* Annexes (previously called Appendixes) are described as 'not part of the code' but provided for information purposes only. Three annexes are included as follows:
~ Annex A – Explanatory Materials (this annex contains much of the material pertaining to detail interpretation on locating/spacing of detectors, circuiting of devices based on class and style etc);
~ Annex B – Engineering Guide for automatic fire detector spacing (provides a 'performance-basis' for the location and spacing of heat detectors with formulas and data on heat release rate for common building materials included).
~Annex C – Referenced publications.
Types of Alarm System Detection and alarm system prescribed ranges from the simplest one or two point manual alert system to the most complex detection, monitoring and alarm system with interlinks to central monitoring stations, building automation and security systems. An understanding of the type of system possible or prescribed in BS5829 and NFPA72 is essential before an in-depth description on wiring practice and power supplies can proceed.
BS5839-1 approaches system design by defining fire protection needs based on categories of protection as follows:
*Type P – Protection of Properties
P1 – All areas covered with detectors except voids less than 800mm in height
P2 – Defined areas in a building having a high fire risk.
*Type L – Protection of Life
L1 – Same as P1
L2 - Same as P2 but for areas with high fire risk to life
L3 – Protection of escape routes
L4 – Protection of circulation areas (2002 edition)
L5 – Fire engineered solution to meet criteria of fire safety & protection of properties (2002 edition).
*Type M – Manual System
*Suffix X – System with multi-occupancy use.
BS5839-1 do not specify the type of system to be used but prescribes consultation with interested parties such as the authorities, property owner, insurance company and others. Factors which may determined the choice of system type include consideration for life and business risk, legal requirements, insurers requirements, maintainability etc. Appendix A (extracted from Annex A of Standard illustrate range of current custom and practice.
NFPA72 do not specify the type of system to be used (manual or automatic detection and at which location etc) but merely specifies the performance criteria, design features, installation method and maintenance procedure for fire alarm system. NFPA 72 recognises that consideration for active and/or passive fire protection system should be integrated as a 'life safety plan' which take into account other aspect of fire safety such as prevention, egress, protection and particular aspects of occupancy. NFPA 101 'Life Safety Code' contains detail prescriptions on the type of systems recommended for the various types of occupancies. In keeping with the 'manual style' format of NFPA72; fire alarm systems are classified as:
* Household fire warning systems;
* Protected premises for fire alarm systems (this class of fire alarm include most systems designed for apartments, offices, industrial buildings etc.);
* Supervising station for fire alarm system (this include specification for communications between alarm system and supervisory station which may be local, remote or municipal master fire alarm panel).
A Comparison of BS5839 and NFPA72 shows the major difference or similarity in style and content of both codes:
Structure of Code BS5839 is structured into parts each of which self-contained within its own rights. NFPA72 is written in a comprehensive manner with chapters containing all aspect of fire alarm system.
Revision Cycle Editions for both codes showing revision cycles are as follows:
~ BS5839-1 1980, 1984, 1988 and 2002
~ NFPA72 1990, 1993, 1996, 1999, 2002
Scope Both BS5839 and NFPA do not specify the type of system for the various types of occupancies or premise. BS5839 recommends consultation with interested parties (authorities, owner, insurer etc) whilst NFPA72 specifically refers to NFPA101 'Life Safety Code' for prescription on the type of systems to be installed for various occupancies. Thus both codes limit themselves purely to a specification on the design features, installation aspect and maintenance procedures for fire alarm system,
Coverage Due to the structure of BS5839, part 1 by itself however do not contain detail specifications for components of fire alarm system (such as detectors, manual call points etc.), voice alarm, emergency voice communication system and small alarm system in dwellings as they are covered in other parts of BS5839. or other BS (BS EN54). NFPA72 in comparison include all scope not included in BS5839-1 (refer section 2.1 above). BS5839 taken as a whole (i.e. including all parts) however can be said to be similar in scope and coverage of NFPA72.
Language Style BS5839 is written generally in the format of a 'guide' with 'recommendations' setting out performance requirements whilst NFPA72 is written in the style of a manual. The manual style of NFPA72 contains detail installation and design guide whilst BS5839 is a little sketchy on details.
Details BS5839 has less details on installation and design issues keeping instead to setting broad criteria of design whilst NFPA72 is full of details pertaining to design and installation, example:
~ BS5839-1 recommendations on circuit "survivability" are brief clauses such as "a fault on one zone shall not prevent the operation of the system in other zones..." or "A single fault shall not remove protection from an area greater than that allowed under 7.2(a) ..." etc. Designers and installers of alarm system are presumably left to decide on system hardware and wiring to comply with the above.
~ In comparison NFPA72 defines circuit "survivability" in terms of circuit class and/or style. The class and style designation contain details which specifically prescribe how hardware and circuits should be configured .
Fire Zones
Both BS5839-1 and NFPA72 contain similar concepts of fire zone with minor differences mainly on the system of units. Maximum area for one fire zone is specified as 2,000m² for BS5839-1 and 20,000ft² (or 1,860m²) for NFPA 72.
Classification of System Types BS5839 classifies system types based on fire protection needs; type P for protection of properties, type L for protection of life and type M for manual system. In BS5839-1, the types of system determines system configuration (detectors coverage, manual call points etc). NFPA72 do not have such a classification concept similar to BS5839-1 but instead rely on NFPA101 to determine fire needs for system configuration. Section 2.2 has details of system types.
Spacing of initiating devices The location and spacing of initiating devices (heat/smoke detectors) is prescribed as follows:
~BS5839-1 is specific on spacing as follows:
smoke detectors under flat ceiling – 7.5m
heat detectors under flat ceiling – 5.3m
in corridor under 2m wide detector spacing may be 15m (smoke) and 10.6 (heat);
detector density may be generally calculated at 100m² (smoke) and 50m² (heat);
On pitched roofs with detectors at or near the apex distances increase by 1% for each degree of slope to a maximum of 25%.
manual call points are recommended at 30m travel distance.
~NFPA72 has a performance oriented approach with regards to detectors spacing:
No exact figures are prescribed but detector spacing should be based on 'listed' spacing.
A figure of 30 ft (9.1m) is quoted as a guide for spot type smoke detectors but with caveat on complying with manufacturer's instructions.
Correction factors to 'theoretical' spacing (i.e. listed or manufacturer's recommendations), include consideration for pitch roof, ceiling heights, corridors etc. which are listed in great details (especially in Annex A).
Location of additional manual call points are recommended at 200ft (61m) travel distance (compare with BS5839-1 prescription of 30m).
Listed is defined in NFPA "included in a list published by an organisation that is acceptable to the authorities having jurisdiction and concerned with evaluation of products or services ...". Examples of a listing organisation is "UL".
Circuit Design again illustrate the difference between the depth of details contained in BS5839-1 and NFPA72.
~BS5839-1 contains general recommendations for "circuit integrity" which are performance oriented in aspect.
~NFPA in contrast though also containing requirements for "circuit survivability" similar in nature to BS5839-1 include detail classification of circuit 'class' and 'style'.
Power supply Both codes similarly prescribed secondary or standby supplies using batteries with or without generator backup. Differences relates to interpretation of 'operational time' (which is the operation time required after basic 24 hours quiescent operational capacity):
~Under BS5839-1, operation time is generally interpreted as 30 minutes of maximum alarm loads (i.e. all sounders ringing) during fire conditions;
~NFPA72 defines operation time as 15 minutes of maximum load during fire conditions (i.e. with sounders ringing).
Cables and Wiring Requirement Both codes similarly prescribed fire rated or 'enhanced' cables with differences in defining performance ratings for 'enhanced' or fire rated cables. The definition of fire-rating between the British (and by extension European and IEC) standards and the NFPA (north American and ANSI) standards has differences which will be described in greater details in section 5.
~ The 2002 edition of BS5839-1 contain major enhancement to the recommendations on use of 'standard', 'fire-rated' and enhanced cables. Other BS codes are referenced in defining standard tests for enhanced or standard cables.
~ NFPA72 contain only a brief reference to cabling requirement. The brief referral however point to NFPA70 ('National Electrical Code') Articles 760, 770 and 800.
Other Major Differences or Similarities between the two codes include the following:
~ The 2002 edition of BS5836 include major enhancement with new subjects some of which are not included in NFPA72:
A new section address issues of false alarm by defining false alarm and steps to mitigate such false alarms (no equivalent in NFPA72).
Additions to section 6 (maintenance) champions the concept of continuous monitoring of system functions (a useful concept where legislative measures for re-certification or regular certification of premise is to be enforced) (no equivalent in NFPA72).
Performance based design is given due recognition with addition of new system type L5 ('engineered solution'). A new BS document PD 7974-4 "Fire safety engineering principles in building; part 4 – detection of fire and activation of fire protection system" (2003) contains guidance on development, design and application of performance based solutions for fire alarm system. (NFPA72 already contain substantial information on this subject as annex).
~ NFPA72, since the 1999 edition include substantial information material for designing to 'performance-based' criteria.
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1) Abstract and Introduction
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2 comments:
Thanks fir this very helpful comparison...well done
waiting for having a contact with you
usama811@hotmail.com
One more issue the looping of devices as per NFPAA & BS 5839.In NFPA the initiation devices(detectors) and notification devices(strobe, horn) have to be in different loops. In BS they can be in same loop.
The voltage as per NFPA for 24V DC control panel is 16V to 33V.
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