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