Catering extract ventilation--prohibition on fitting of fire dampers

[Nimrod]

I believe BS 5588-9 Fire precautions in the design, construction and use of buildings Part 9: Code of practice for ventilation and air conditioning ductwork specifies that non-domestic kitchen extract ducts should not be fitted with fire dampers.

I'm curious to know the reason for why this approach has been adopted in the standard. Different jurisdictions take a different view. Some promote the fitting of dampers while others  don't.

Does anyone know what lead the standards committee to specify the no dampers approach?

As always grateful for any advice or guidance that the forum members wish to share.

B:)

[AnthonyB]

Perhaps dampers would be susceptible to grease build up affecting their efficacy and being a fire risk in themselves plus would make duct deep cleaning more difficult?

[Nimrod]

Thank you Anthony for your point about grease interfering with the operation of the fire dampers.

Perhaps the standards committee concluded that in the past fire dampers have not been effective and that a better way forward would be to engineer them out by improving the fire performance of the extract duct both from fires within and without.

If this was the case I wonder if there is any evidence for this.

Or maybe it was about keeping the kitchen clear of smoke in the event of a fire?

It occurs to me there may be a health and safety angle. If the fire damper dropped in the extract system it would mean the kitchen staff would be exposed to fumes from cooking and gas appliances which could be injurious to health.

I'm sure the committee thought long and hard about the matter and I'm just curious to know why they opted for no fire dampers in the duct.

Again Anthony thank you for your comment.

B:)

[wee brian]

Its the grease issue - not only does it interfere with the damper but there is also a real potential for the fire to skip past/through the damper.

Standard dampers dont have any insulation so they get hot.

If the grease in a duct is burning then it may well flash up the duct faster than the damper will operate.

[Psuedonym]

When a fire suppression system is installed the vents in a kitchen hood cannot be closed in the event of a fire. Ansul (and others) provide fire cover within the vent/s of hoods to eliminate the spread of flames through vents in the standard system design.
"Exhaust fans in the ventilating system should be left on. The forced draft of these fans assists the movement of the liquid agent through the ventilating system, thus aiding in the fire suppression process. These fans also provide a cooling effect in the plenum and duct after the fire suppression system has been discharged.  Air supply fans integral to the hoods being protected shall be shut down upon system actuation"  

There are also electrostatic precipitators fitted in some vents to aid the cleaning of exhaust air. Nozzles are installed prior to and above the precipitator to ensure vertical protection throughout the vent.

A bigger issue with cooker hoods is the huge build up of grease etc providing a fire risk because companies are skimping on effecive hood cleaning practices. Deep cleaning does not include the suppression system pipework and detectors as the cleaning companies are afraid of activating the fire protection system during cleaning. Ideally the suppression system (as per recommendations) should be isolated prior to cleaning but co.s can't or won't pay for a fire company to provide this service. Therefore the detection system builds huge quantities of sh~t.
Not nice to service and providing a lovely fire risk.

[Nimrod]

I now understand the reason for no fire dampers in kitchen ducts is so the brigade can use the ductwork and fan to clear the area of smoke.

[wee brian]

Who told you that?