Issue 40 winter 23 web - Flipbook - Page 69
3. Aspiration or air sampling smoke detection is an
extremely sensitive form of detection often used in large
spaces with very high ceilings where standard devices will
not operate. It works by drawing air through a network
of pipes, sampling the air for smoke particles. This enables
very early detection and allows enough time for the
building’s occupants to vacate the premises. This is often
the best choice for cathedrals and other very large
buildings where time to evacuate is essential given the
quantity of people that could need to escape. These types
of systems are known by a variety of names but the most
well-known are VESDA (Very Early Smoke Detection
Apparatus) and ASD (Air Sampling Detection). The
biggest issue with this type of detection is that without
proper maintenance the filters can become blocked with
dust and dirt, rendering them less effective.
As part of determining the type of system that should be
used the building owner/custodian or their fire advisor
must conduct a thorough risk assessment. In simple terms
this means looking carefully at the building and the people
who use it and understanding the risks.
Broadly speaking assessments are conducted in five key
steps: • Identify the fire hazards
• Identify the people at risk
• Evaluate, remove or reduce the risks
• Record your findings, prepare an emergency plan and
provide appropriate training
• Review and update the fire risk assessment regularly
Unfortunately, statistical evidence shows that a high percentage of fires in historic buildings have needed the local
fire and rescue services to attend and Historic England
research from 2019 shows that there have been the following number of incidents which have impacted: • 15 grade I listed buildings
• 47 grade II* listed buildings
• 343 grade II listed buildings
• 16 world heritage sites
• 554 conservation areas and locally listed buildings
which makes for startling reading.
4. Beam detection is for those that do not wish to employ
an aspiration system, the downside is that they will have
a greater visual impact to a heritage interior and there is
a restriction on how far apart the two component
parts can be from each other. This distance varies from
manufacturer to manufacturer but typically the detector
and reflector plate must be a minimum of 40 metres apart
and set down from the ceiling by between 475-600mm.
The best approach for installing any of this equipment
within an historic interior is to initially establish what
decorative and structural features such as beams, ornate
ceilings, painted or stencilled finishes, panelling and
decorative plaster work exist.
Historic England suggests using a minimum of P1 fire
alarm system within listed buildings as it provides the
maximum protection to the building fabric. Our preferred
recommendation is a L1/P1 system to provide maximum
protection to both the listed/historic property and the
occupants.
Then ensure that you locate a device where it still
operates but is disguised by a building feature or is colour
matched to blend in with a decorative ceiling. Any
adjustments to colour or finish must be done in conjunction with the manufacturer to avoid nullifying any
product guarantees or warranties.
The main components of a modern fire alarm system are
as follows.
1. Fire alarm panel which is the main point of reference
for both the building occupants and the fire and rescue
team. Panels are required on conventional, addressable
and wireless systems. With addressable systems the panel
will provide precise locations of the activated devices as
each has its own unique electronic address. With wireless
systems the panel uses a secure wireless connection
between the sensor and the panel.
This approach will often result in a design not entirely in
accordance with the British Standard, but it should be
remembered that these are advisory documents and not
statutory.
For more detailed information see Historic England’s fire
alarm guidance and technical webinar recording: • https://historicengland.org.uk/advice/technical-advice/building-services-engineering/fire-alarms-for-historic-buildings/
Wireless systems are a good option for listed buildings
because this results in the minimum amount of cabling,
chasing and hole drilling. It will however require a signal
strength survey and booster aerials where needed but has
a lot of advantages where installation time and disruption
are concerned and in preserving historic fabric and
interiors.
• https://historicengland.org.uk/advice/technical-advice/building-services-engineering/fire-alarms-for-historic-buildings/designing-installing-and-maintaining-a-fi
re-detection-and-protection-system/
2. Detection heads can be for automatic sensing a variety
of fire related symptoms such as smoke, heat, carbon
monoxide. Under this heading also comes manual
break-glass units where a person sounds the alarm upon
discovering a fire.
• https://historicengland.org.uk/services-skills/trainingskills/training/webinars/recordings/webinar-on-firealarm-systems-in-historic-buildings/
i
i
Conservation & Heritage Journal
67