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Plugholing

The document discusses the phenomenon of plugholing in smoke control systems. Plugholing occurs when fresh air is pulled into exhaust inlets, decreasing the efficiency of smoke removal and allowing deeper smoke layers that can expose occupants. To treat plugholing, the amount of air extracted from each inlet must be limited and inlets placed far enough from each other. Several standards like BS7346, NFPA92, and guidelines provide methods to calculate critical mass flow rates and place inlets to prevent plugholing. There are open questions around minimum smoke temperature rises required for effective smoke control and high flow rates needed to prevent plugholing with long spill widths.

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irfan
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320 views10 pages

Plugholing

The document discusses the phenomenon of plugholing in smoke control systems. Plugholing occurs when fresh air is pulled into exhaust inlets, decreasing the efficiency of smoke removal and allowing deeper smoke layers that can expose occupants. To treat plugholing, the amount of air extracted from each inlet must be limited and inlets placed far enough from each other. Several standards like BS7346, NFPA92, and guidelines provide methods to calculate critical mass flow rates and place inlets to prevent plugholing. There are open questions around minimum smoke temperature rises required for effective smoke control and high flow rates needed to prevent plugholing with long spill widths.

Uploaded by

irfan
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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SMOKE CONTROL -PLUGHOLING

Written and compiled by


Ir. Tan Yoke Lee
MIEM, Mi-FIRE-E
yokeleetan71@gmail.com
SMOKE CONTROL -PLUGHOLING
Plugholing is the phenomena whereby fresh air is being pulled into the exhaust inlet for systems in
which the “headroom” for accumulation of smoke above the highest egress route is minimal. This
“plugholing” of the exhaust inlet by the fresh air can decrease the efficiency of the smoke exhaust
system and can result in a deeper layer of smoke, to which occupants may be exposed (Figure 2).
SMOKE CONTROL -PLUGHOLING
Treatment of plugholing is by limiting the amount of air that can be extracted from each exhaust inlet
and to place the inlet sufficiently far enough from each other. Extracted from article Smoke
management: Atriums and plugholes by Lougheed
SMOKE CONTROL -PLUGHOLING
Treatment of plugholing is by limiting the amount of air that can be extracted from each exhaust inlet
and to place the inlet sufficiently far enough from each other. Extracted from British Standard 7346
part 4
SMOKE CONTROL -PLUGHOLING
Treatment of plugholing is by limiting the amount of air that can be extracted from each exhaust inlet
and to place the inlet sufficiently far enough from each other. Extracted from Guide to Fire Protection
Malaysia

Similar to BS7346 for critical mass flow, using equation


where the ventilator is further from the wall than the
characteristic width of ventilator equation F.10
SMOKE CONTROL -PLUGHOLING
Treatment of plugholing is by limiting the amount of air that can be extracted from each exhaust inlet
and to place the inlet sufficiently far enough from each other. Extracted from NFPA 92
SMOKE CONTROL -PLUGHOLING
Treatment of plugholing is by limiting the amount of air that can be extracted from each exhaust inlet
and to place the inlet sufficiently far enough from each other. Extracted from NFPA 92
SMOKE CONTROL -PLUGHOLING
Treatment of plugholing is by limiting the amount of air that can be extracted from each exhaust inlet
and to place the inlet sufficiently far enough from each other. Extracted from NFPA 92
SMOKE CONTROL -PLUGHOLING
A comparison was made calculating the critical mass flow rate for plugholing.
Using NFPA92, a value of 6.7 kg/sec is obtained while using BS7436 a value of 9.16 kg/sec is obtained for flow through wall outlet.
This means a lot more ventilators are required in NFPA92 as compared to BS7346.
However, K=0.5 is used in NFPA calculation resulting in lower smoke temperature and To= 70deg F is used. In BS7346, K=1 for Ts
and To=92 deg F for summer time.

BS 7346

NFPA 92
SMOKE CONTROL -PLUGHOLING
POINTS FOR PONDERING

It is noted that in NFPA92, the minimum temperature rise of smoke above ambient is 4 deg F.

In BS 7346, design temperature of smoke layer shall not be less than 20 deg C above the ambient temperature
and if less than 50 deg C, the depth of the smoke layer, Y in table 2 shall be increased by 0.5m.

Here rise the question as to what is the minimum temperature of smoke above ambient for smoke control
engineering to work? This would need careful consideration and comparison to CFD calculations.

Also, it seems that for spill plume, the flow rate required is high if the opening width of the spill and balcony
projection is long. This would require lots of ventilators to avoid plugholing.

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