Using Fire Dampers in Kitchens

The BRANZ Guide to Passive Fire Protection in Buildings provides an excellent overview of the regulations. It identifies the principles of NZ Building Code, explains the terminology commonly used and talks to the main components which have a passive fire protection role.

 

The term ‘Passive Fire Protection’ refers to the construction elements within a building that are designed to prevent or delay the spread of fire and/or smoke to different parts of the building. This differs from active fire protection, which would include the use of sprinklers and suchlike to actively manage the fire. Passive fire protection has two key aspects:

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• Resistance to fire. Such as the ability of a fire-separating element (i.e. wall or floor/ceiling) to limit fire spread, including passage of fire products through the elements, or to prevent collapses in the case of a load bearing element (such as a column).

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• Reaction to fire. Such as the surface burning behaviour of an element or material and the extent to which it promotes rapid flame spread or smoke production.

 

 

In standard homes, or apartments with a timber mid-floor structure, ventilation grills in the ceiling should be protected. The most common way of doing this is through the use of an intumescent fire damper. These allow the flow of air through fire rated walls and ceilings. If a fire breaks out, the rising temperature will cause the intumescents to expand, closing the gaps in the grill to prevent vertical fire spread. An intumescent will typically expand at a rate of 50:1. This means that a 1mm coating will reach an estimated density of 50mm in the event of a fire.

 

 

It is possible to avoid the use of a fire damper by running the ducting through a bulkhead, although doing so isn’t desirable aesthetically. In apartments, another alternative is the use of a false ceiling. Some apartments with a timber mid-floor structure will increase the floor separation from 2.7 to 3 metres, allowing for a false ceiling, creating a channel between it and the fire barrier above for services and ducting.

 

 

Kitchen range hoods present another complication. Ideally, they will be located by an external wall so they’ll be ducted to the outside. That’s not always the case in apartments (or in some houses) and it means adaptation is needed. If there’s no false ceiling to contain the ducting from a range hood, a fire damper is needed. This might not sound like an issue, given they’re used in the laundry and bathroom. However, a range hood will become covered in grease and that is a problem. Intumescents are quick to expand but they still take time. With all that grease, the risk of flames licking through the grill and igniting it, is just too great. For this reason we don't recommend, nor will we install, a ceiling mounted fire damper from a kitchen rangehood.

 

 

One alternative is to use a more expensive spring loaded steel damper. Yet with moving parts needing regular maintenance, possibly every 3 months, we feel they present a risk too. Without any guarantees the regular maintenance will take place, we preclude these from consideration.

 

 

When it comes to extraction ventilation in New Zealand homes, passive fire protection is both simple and complex. The regulations are easy to understand but implication comes with complication. Such as the issue with kitchen range hoods. The only consistency is the need to do it properly. The consequences of not doing so, and we make no apologies for appearing dramatic here, can be fatal.

 

 

If you have a building project and would like some advice on ventilation design then please contact us. We’re here to help.