A properly designed and installed fire curtain will deploy time and time again without any problem. BS 8524-1 includes a reliability test where the curtain is cycle tested to prove reliability of operation over an extended period.
What can go wrong? Excess pressure differences
However, it is quite possible for a fire curtain to stick if subjected to excess pressure differences or air velocities while it is deploying. The problem is that the pressure or velocity pushes the fabric and its end guides against one side of the side guide rail and the resulting additional friction can overcome the gravitational force and stop the curtain in its tracks.
The causes of pressure differences
The main causes of these pressure differences are mechanical smoke extract or pressurisation systems and pressures generated by the fire itself.
If the smoke extract fans operate before the fire curtain deploys, and particularly if there are limited openings for air inlet, then those extract fans can create quite a large pressure differential.
Stair pressurisation systems and mechanical smoke shaft systems create quite large pressure differentials by design, up to 60Pa in the case of pressurisation systems.
Fires generate pressures due to the buoyancy of the hot smoke and gases generated. Pressures in a typical room might reach 5-20 Pa, although this can be reduced by provision of smoke ventilation.
So, how do we minimize the risk of sticking?
For mechanical smoke control and pressurisation systems it can be achieved simply by deploying the fire curtains before the fans are started. We would recommend that a delay of at least 60 seconds is built in to the fan starter circuit.
Fire pressure increases as the fire grows. In the early stages pressures are very small, so a fire curtain linked to a detection system will normally operate long before fire pressure might become a problem.
When you might need an engineering assessment
An exception to this is where fire curtains deploy to an intermediate position before descending to the floor. In this instance pressures could build up, though since the temperatures at the bottom of the curtain are lower, these pressures will tend to be lower. An engineering assessment might be needed in such cases.
Smoke curtains generally do not suffer from the same issues as most do not have side guides or completely close an opening, although if they do then the same considerations apply.
The solution: deployment before reaching high pressure differences
If properly designed, installed and commissioned, and if deployed before high pressure differentials are reached, fire curtains can be expected to operate reliably and provide the level of protection intended.
To find out more, download our whitepaper entitled “Design considerations when integrating smoke and fire curtains into a building”. It covers:
- What are smoke curtains and fire curtains and what are the key differences between them
- The standards which each type of system has to comply with
- The design aspects to consider when integrating these systems into a building
- Installation, use, testing and maintenance.
Or watch a recording of our webinar on the same subject.
Paul Compton is Technical Director for Colt, experienced in smoke control, HVAC, solar shading and louvre systems.