Cold Link Africa Jan/Feb 2017 | Page 41

INCORPORATING COLD CHAIN
FEATURE

ASD in cold store and freezer environments ( Part 2 )

By Kevin Botha of Xtralis

We continue from the September / October issue , looking at possible pitfalls of installing an Aspirating Smoke Detector ( ASD ) — a technology originally developed to provide early warning of incipient fires in telecom and data facilities .

In Part 1 , we looked at how ASD has evolved to provide effective protection in cold stores and freezers .
important to verify that the selected product can provide enough sampling point holes to cover the area to be
A third , but vitally important , consideration is lifetime performance .
Like all optical smoke detection
It is generally accepted that ASD
protected adequately . Manufacturers ’
systems , ASDs are prone to the effects
provides the earliest possible warning
product data sheets should clearly state
of contamination from constantly
of fire , but what are the possible pitfalls
this information as well as the product ’ s
passing air across optical components
and what should stakeholders consider
associated class compliance . However ,
in the detection chamber . Advanced
with respect to product and installation
there is no requirement under the
ASD systems use filters to remove more
to ensure that an ASD system provides
EN54-20 standard for manufacturers to
than 99 % of contaminants from part
reliable and trouble-free protection for
publish this data and some make the
of the air sample to provide a clean
their cold store or freezer facility ?
information difficult to find .
air barrier across sensitive optical
The ASD should provide a wide
components . This ensures that the
Product
sensitivity range with multiple staged
detector ’ s design performance is
A first consideration should be product
alarms . That will provide the user with
maintained over the product ’ s lifetime ,
Figure 1 : Cold storage sampling kit for warehouse .
quality and in the fire detection
an early warning Class A or B alarm for
that service life is increased , and that
industry , we are fortunate that products
early intervention — in layperson ’ s terms
lower ongoing maintenance costs are
are rigidly tested to meet national
a ‘ please investigate there is something
achieved for the user .
and international standards . EN54-
wrong ’ condition — as well as a later
Less advanced ASDs employ lower
20 is a product standard specifically
standard sensitivity Class C alarm , aka
cost software algorithms to alter the
developed for ASD systems , which has
‘ there is a confirmed fire , please activate
calibration of the detector artificially as
been adopted across all EU countries
fire extinguishing protocols ’. The ASD
it ages and becomes contaminated ;
as well as South Africa under SANS
should be able to provide the staged
an approach that is always a
50054-20 . While the approval provides
alarms from a single detection device to
compromise because it inevitably
confidence that an independent
keep costs down . There is little advantage
affects the system ’ s detection
third party has thoroughly tested the
in installing two low-cost ASD units —
performance and may even change
product , there is no guarantee that it
one to provide an early warning alarm
the intended class compliance . To
is suitable for use in harsh environments
and another to provide a confirmed
clarify why this is so important : ASDs
such as cold stores and freezers ,
fire alarm — when a single , slightly more
are designed , installed , tested and
and stakeholders should explore in
expensive ASD can do both . As can be
commissioned to provide optimal
some detail the product ’ s technical
seen , manufacturers ’ published EN54-
detection performance , which is just
Figure 2 : Sampling point line drawing .
capabilities as well as its history of
20 performance data becomes quite
sensitive enough to provide the earliest
successful installations .
important in helping with the choice of
possible warning , but at the same time
flexible when it comes to design . It is easy to meet
For example , EN54-20 defines the
suitable product . Lower cost products
avoids the probability of unwanted
prescriptive design and installation standards while
number of sampling orifices that an
that often don ’ t have the data readily
or false alarms . That is a fine balance ,
at the same time exceeding those requirements
ASD is capable of supporting , and it is
available should be treated with caution .
which is relatively easily achieved
to provide improved performance for the user .
through a structured specification ,
A performance based approach , rather than a
design and commissioning process
simple ‘ deemed to comply ’ solution is therefore
with guidance from manufacturers
easily and cost effectively achieved . That
and associated application standards
approach adds measurable value to the detection
documents . With that in mind , there is
system ; something normally not easily achieved
little point in going through the process
with fire detection .
of testing and optimising a low-cost
For instance , sampling holes can be positioned
ASD system if its detection performance
in locations where fire is most easily and quickly
drifts from original design and intent .
detected . Very often that is not where a ‘ deemed to
There is also a resulting risk that fires may
comply ’ design tells us , but rather where air movement
be detected later than was intended ,
due to chilling equipment transports the smoke .
with subsequent associated loss .
Sampling pipe can be positioned inside the
protected area below the ceiling , a technique
Design and application
that minimises the number of penetrations through
Similar to other smoke detection
walls and ceilings . Alternatively , sample pipes
technologies , for example point type
can be positioned outside of the chilled area with
detectors , the quantity and positioning
penetrations at each sampling location . While
of ASD detection points or sample holes
the latter method seems more complex , it has
is governed by prescriptive standards
proven to be the most effective at reducing the
such as SANS-10139 . However , the
risk of condensation and icing in sub 0 ° C freezers .
principle of transporting air samples
Innovative design of newer ‘ through ceiling ’
along a network of sampling pipes
ASD is useful as early warning of incipient fires in warehouses and cold storage .
means that ASDs are inherently
Continued on page 43
COLD LINK AFRICA • January | February 2017
www . coldlinkafrica . co . za

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