Smoke control is a critical part of any fire protection strategy, and yet the requirements for smoke seals on fire curtains lead to designs that we believe are not fit for purpose. In this article we describe why this is and how it could change.
Why do we need smoke control in a fire?
The National Library of Medicine found “approximately 80% of fire-related deaths are due not to the airway burn injury itself but to the inhalation of toxic products, especially carbon monoxide and hydrogen cyanide gases.”
During a fire, smoke is released. According to an article on the FireFighter Insider.com website, ‘Black Smoke: What Does It Mean And What Causes It?’, smoke is an aerosol comprising ‘tiny particles of either partially oxidised, fully oxidised or unreacted fuel particles’. It is usually highly toxic and, combined with the removal of oxygen from the air, leaves building users trapped by fires with nothing but dangerous particles and gases, and carbon dioxide to inhale.
Smoke inhalation can result in serious, even deadly Smoke Inhalation Injuries (SIIs). Even in the best-case scenario, SIIs often result in an extended stay in intensive care, requiring ventilation due to the increased possibility of developing pneumonia. Another article, by the Fire Industry Association, shows how smoke exposure from intense fires is linked to long-term respiratory and cardiovascular disease.
For these reasons, you can see how critical it is that fire curtains should come with smoke control to mitigate the spread of smoke in a building during a fire. What’s more, it is essential that this smoke control works in a fire situation, not only under ‘cold’ test conditions.
What are cold smoke seals, and do they work in a fire?
Cold smoke seals are manufactured from polypropylene (‘PP’) filament. According to the ASFP’s Black Book (‘Active Fire Curtains: Compartmentation and Protected Routes’, 1st Ed. 2020, page 23), cold smoke seals should ‘…enable a fire curtain to be used on protected escape routes where fire door flexible edge seals are normally recommended’. This is due to their ability to block the passage of smoke through the side guides and headbox on the fire curtain, keeping critical areas clear of smoke for longer and reducing the likelihood of building users breathing in harmful particles and gases.
Fire curtains that use these cold smoke seals fix the polypropylene brush in the guides of the curtain as shown in Fig 1, and in the headbox where needed.
This polypropylene brush has a melting temperature of around 170°C, which will last less than 5 minutes under the conditions of the industry standard fire test.
The standard used to ascertain the fire performance of a fire curtain and many other fire products is BS EN 1634-1:2014+A1:2018, which stipulates that the test is conducted using the equipment and procedures in accordance with EN 1363-1. This document shows that the temperature has reached 576°C after just 5 minutes in a fire test (see the temperature/time curve in Fig 3).We have included Fig 2 alongside Fig 1 to show another way to achieve smoke sealing in a fire curtain, and we touch on this in more detail below.
Going back to the melting temperature of the polypropylene cold smoke seals, it is important to consider that the fire curtain is often designed and specified to provide 120 minutes of radiant heat protection in a fire, and the fire strategy for the building and the design of the escape routes will all rely on this – and yet, fire curtains using cold smoke seals do not provide more than 5 minutes of smoke control in fire situations. In view of the dangers of smoke inhalation, this mismatch calls into question the ability of these curtains to adequately protect escape routes for the occupants of a building.
To address this deficiency, we could consider the approach used for fire doors. FireSealsDirect tells us that ‘Smoke seals are often used in conjunction with intumescent strips, but it isn’t an either/or situation. Intumescent strips are required to be fitted to any fire door, and so if you fitted a smoke seal (to help prevent spread of smoke), you would still be required to fit an intumescent strip to help protect against fire. It’s very common for intumescent strips and seals to be bought and installed together.’
In this concept, the cold smoke seals act to prevent cold smoke spreading in the early stages of the fire, and when the temperature rises, the intumescent strip will ‘take over’.
At Adexon, we take the statement from FireSealsDirect further and advocate that changes are made to the relevant legislation and Building Regulations to mandate that ‘cold smoke seals MUST be protected from the effects of heat in a fire, or supplemented by the use of an intumescent strip or similar when the temperature exceeds their operating limits’.
So why not just fit an intumescent strip to a fire curtain?
Unfortunately, intumescent strips cannot be fitted to fire curtains to protect or ‘take over’ from the cold smoke seals for fear the intumescent strip will expand in the heat (as it is designed to) and block the route of travel for the fabric, preventing the fire curtain from even deploying.
The absence of accompanying intumescent strips on fire curtains is the critical deficiency with using cold smoke seals on fire curtains compared with fire doors. The smoke seals on a fire curtain are exposed to fire temperatures from the start and, in these circumstances, they cannot last even 5 minutes. You can see in this fire door test video how smoke and hot gases spread incredibly quickly if there are no intumescent seals fitted.
If cold smoke seals don’t provide smoke control in a fire, why were they ever invented?
As previously explained, cold smoke seals were originally developed for use on fire doors in conjunction with intumescent strips, and this approach is very effective in restricting the passage of smoke in a building. Their use on fire curtains is more problematic, but there are two reasons why some products feature them:
1) Because they work well under certain conditions: the polypropylene brush is ideal in a cold or ambient temperature laboratory situation where it presses lightly against the curtain fabric on both sides to form a complete seal around the curtain and thus prevent or slow the spread of smoke. The brush allows for the free movement of the fabric while also being stiff enough to withstand differences in air pressure that would otherwise carry the smoke around the curtain.
2) Because the standards allow it: the smoke test BS EN 1634-3 is only performed at cold (ambient) temperatures. This is insufficient when we want to be protected from smoke in a fire situation and is one reason why we believe the existing test method or standard needs to be revised and improved.
The polypropylene material from which the cold smoke seals are manufactured loses its structural integrity before reaching its melting point, and auto-ignites as the temperature increases further (at circa 200°C).
It is therefore clear that, while cold smoke seals comply with current test standards, most designs are inadequate for coping with a realistic fire scenario.
So can you have fire curtains that provide smoke control in a fire?
As shown above in Fig 2, a better design of smoke sealing on fire curtains is available, meaning you can still use your favourite method of active fire control for containment and compartmentation and have peace of mind.
Adexon’s unique and industry-leading guide design uses a proprietary fireproof fabric to provide the smoke sealing. This is secured to the inside faces of the side guides and headbox using steel brackets and stainless-steel rivets.
This Adexon fireproof fabric is stiff enough not to yield and hence forms a tight seal to control the spread of smoke, as well as being sufficiently flexible to allow smooth unhindered operation of the fire curtain.
Additionally, the proprietary Adexon fireproof guide design uses materials that can withstand fire temperatures; the fabric is tested to above 1000°C and the steel components have a melting point between 1350°C and 1530°C. Although not yet tested as an assembly (there is currently no standard against which it can be tested), the material science points to smoke control and containment by the fire curtain under realistic fire conditions.
If you are unsure about the type of smoke seals in your fire curtains, contact us and we will be happy to come and survey your premises and advise you on the options available.
A version of this article has been published in the Winter Edition of the Door Industry Journal.
This article was written in October 2022 by the team at Adexon Fire & Smoke and revised in February 2023.