Guidance for Coincidence Connection of Detectors for Triggering Extinguishing Systems
This guide is a collation and explanation
of the existing recommendations provided on the use of coincidence connected
detectors with a particular focus on their application for triggering
extinguishing systems. It defines a scheme for describing the different
approaches to coincidence connection and in particular considers potential
replacements for ionisation detectors.
Although predominantly aimed at assisting
those involved in the automatic release of extinguishing systems, this FIA
guide also provides information in situations where coincidence of detectors is
needed for the actuation of other fire protection measures.
Review of Standards
There is a
common misconception that BS 7273-1 Clause 5.2.3 calls for coincidence
detection using two different types of detector, typically ionization and
optical smoke detectors to trigger fire suppression systems. This is not
correct.
5.2.3 Type of detector used
The
selection of detectors should be in accordance with the recommendations given
in BS 5839-1 and, where applicable, BS 6266. In some circumstances, fire
detection considerations might dictate the need for use of two different
principles of detection (e.g. optical smoke detectors and ionization chamber
smoke detectors) to ensure the earliest warning of fire. In such circumstances,
an even distribution of each type of detector should be provided throughout the
protected space.
Where
coincidence is used, normally it should be possible to achieve coincidence from
two detectors of the same operating principle. In these cases, if, for example,
two independent circuits are used to achieve coincidence, there should normally
be an approximately equal number of detectors of each principle connected to
each of the independent circuits. For example, where four detectors are
required to protect the space and these comprise two optical smoke detectors
and two ionization chamber smoke detectors; there should be one optical smoke
detector and one ionization chamber smoke detector on each circuit.
However, it is not always necessary to use
two different principles of fire detection. For example, given the type of fire
anticipated and the speed of detection required, it might be acceptable to use
detectors of a single type.
BS 7273-1 does not require the use of
detectors using two different principles of operation:
·
Clause
5.2.2.1 suggests that co-incidence detection is one method of minimising the
possibility of false discharge.
·
Clause
5.2.2.4 clarifies that co-incidence detection requires alarm signals from two
independent detectors (whether the same type or not).
The second paragraph of clause 5.2.3
(above) was originally a continuation of paragraph 1 and as a separate
paragraph is now confusing. The intent is to clarify that where mixed types are
used, it is not normal to require both types (e.g. optical and ionisation) to
have indicated an alarm before the extinguishant is released. In other words
extinguishant may be triggered from any two independent detectors e.g.
two ionisation detectors or two optical detectors or an ionisation and an
optical detector.
Clause 5.2.3 only includes as examples the
traditional combinations of optical and ionisation detectors. There are many
other technologies which may be used, for example flame detection, multi-sensor
devices, aspirating smoke detectors (ASD) which can be used to mitigate the
risk of inadvertent discharge of extinguishant.
BS 7273-1 refers back to BS 5839-1 and BS
6266 for advice on the selection of fire detectors. Both these standards have
been revised since BS 7273-1 was published and provide useful guidance:
·
BS
6266:2011 Clause 8.3
·
BS
5839-1:2013 Clause 21
Co-incidence detection is when at least
two independent detectors are used to initiate the release of the extinguishing
system. These can be of the same type or of two different types.
The type(s) chosen should be selected
dependant on the fire risk and on the objectives of the fire system.
Given that ionisation smoke detection is
in obsolescence, the traditional ionisation / optical combinations as
exemplified in BS 7273-1 is losing relevance.
Some common possible alternative
combinations include:
·
Optical
& Optical
Traditional
scatter type optical smoke detectors
o Optical smoke detectors must pass a range
of fire tests including smouldering and flam-ing types and have proved to be
suitable for many applications requiring co-incidence
o Flaming fires will be detected; however
response may be slower than ionisation detec-tors
·
Optical
& Optical-Heat (or Optical-Heat & Optical-Heat)
o
Optical-Heat detectors speed
the response of a standard optical smoke detector to a flaming fire by responding to heat
o
Some Optical-Heat detectors
may respond more slowly to a smouldering fire than a traditional optical detector
·
ASD
& ASD (or ASD & other)
o Very early warning of incipient fires is possible using Class A &
B ASD systems which can
prompt early intervention and avoid automatic discharge of the fire
suppression system
– whether to a real fire threat or an unwanted event (false alarm)
o
ASD
& ASD requires two separate detectors to achieve true co-incidence
detection
o
Inputs
to the extinguishing system must be carefully selected (e.g. Class C only)
o
See
also FIA Aspirating Smoke Detectors CoP
·
Optical
& Flame (or Flame & Flame)
o
Fast
detection of flaming fires
o Flame detector
requires unobstructed line of sight to area of coverage
o
Used
only in special applications where flame is a particular risk
·
Multi-sensor
& Multi-sensor (including dual-optical)
o
Many
different types available with many different modes of operation therefore
careful consideration needs to be made of the configuration of the detectors
o
Often
designed to mitigate nuisance alarm risk and enhance fire detection
·
Heat
& other
o
The
use of heat detectors only is not recommended as heat detector response is very
slow in comparison to a smoke detector
References and Applicable
Standards
BS 5839-1:2013, Fire detection and fire
alarm systems for buildings - Code of practice for design, installation,
commissioning and maintenance of systems in non-domestic premises
BS 6266:2011, Fire protection for
electronic equipment installations. Code of practice
BS 7273-1:2006, Code of practice for the
operation of fire protection measures. Electrical actuation of gaseous total
flooding extinguishing systems.
A small note on FM 200.
🧱 1. What is FM-200?
FM-200 is a clean agent fire suppression gas stored under pressure and released into protected spaces to extinguish fires without leaving any residue.
🧱 2. Components FM-200 System
1. Storage Cylinders:
• Contain FM-200 in a compressed gas state, typically pressurized to 24.8 bar or higher.
• Can be located inside or outside the protected room.
2. Discharge Piping Network:
• Delivers the agent from cylinders to discharge nozzles.
• Designed based on hydraulic flow calculations.
3. Nozzles:
• Distribute the gas uniformly throughout the room.
• Their number, spacing, and type depend on room volume and layout.
4. Control Panel:
• Interfaces with detection devices and controls automatic or manual release.
• Receives signals from smoke/heat detectors.
5. Smoke and Heat Detectors:
• Detect fire early and send signals to the control panel for verification.
6. Abort Switch:
• Allows users to cancel the discharge countdown if fire confirmation is false.
7. Manual Release Station:
• Enables manual activation of the system in emergency cases.
8. Audible & Visual Alarms:
• Alert occupants of imminent discharge with a pre-discharge countdown (typically 10–30 seconds).
