Are cold smoke seals in fire curtains a cause for concern?

Table of Contents

1. Introduction

Smoke control is a critical part of any fire protection strategy.

Whilst hot smoke testing is not yet a requirement of BS EN 1634-31; we believe it should be.

It is widely known that in real life it is the hot gases and hot smoke that do most of the damage, and cause most of the deaths and serious injuries.

A product test such as BS EN 1634-3 should seek to replicate real life as closely as possible, as opposed to suiting the limitations of existing or older products on the market.

We believe it is the responsibility of manufacturers to rise to the challenge of designing and developing products that meet the requirements of real life, especially in the life-safety arena.

In this article we look into:

  • smoke control designs used in active fire curtains,
  • the limitations of some older designs that are still being sold on the market, and
  • a modern design that uses only fire resistant components for smoke control.

2. 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.2

During a fire, smoke is released. According to FireFighter, smoke is an aerosol comprising “tiny particles of either partially oxidised, fully oxidised or unreacted fuel particles3. 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 Association4, shows how smoke exposure from intense fires is linked to long-term respiratory and cardiovascular disease.

These statistics and studies show how critical it is that passive fire compartmentation products such as active 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 when subjected to hot smoke and hot gases. This is why we say BS EN 1634-3 should be revised so testing replicates the hot smoke and hot gases products are subjected to in real life.

3. What are cold smoke seals, and do they work in a fire?

Cold smoke seals are a filament brush strip that is manufactured from the hydrocarbon commonly known as polypropylene (or ‘PP’) (Fig. 1).


Creative Mechanism states “polypropylene is highly flammable”5 and according to TC Forensics6 it has a melting temperature of less than 170°C.

As such, we can see from the heat curve shown in Fig. 2 that polypropylene will melt in less than 5 minutes under the conditions of the industry standard fire test. This heat curve, from BS EN 1363-1, shows that the temperature has reached 576°C after just 5 minutes in a fire test. The standard used to ascertain the fire resistance performance of a fire curtain and many other fire products is BS EN 1634-1:2014+A1:2018. This stipulates that the test is conducted using the equipment and procedures in accordance with BS EN 1363-1.

FireSealsDirect tell us “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.10

In this combination, 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’. A very illustrative example of how this works (and showing how it does not work without intumescent strips) can be seen in this video,

When seeing this video showing how cold smoke seals do not work in a fire on their own, you can understand why we believe legislation should only support the use of cold smoke seals for smoke control on life safety products when used in conjunction with intumescent strips.

4. Cold smoke seals on active fire curtains

ASFP’s Black Book, says “smoke resisting properties… enables a fire curtain to be used on protected escape routes where fire door flexible edge seals are normally recommended7.

These ‘smoke resisting properties’ should prevent 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 cold smoke seals fix the polypropylene brush in the guides of the curtain as shown in Fig. 3, and in the headbox where needed.

Coming 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 fire resistance protection in a fire, and the fire strategy for the building and the design of the escape routes may rely on this.

However, the polypropylene cold smoke seals used in some older traditional designs of active fire curtains will melt in less than 5 minutes. In view of the dangers of smoke inhalation, this mismatch calls into question the ability of fire curtains using cold smoke seals to adequately protect escape routes or any of the building from the spread of smoke in a fire.

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 design 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 as early as the start and, in these circumstances, they last less than 5 minutes. You can see again in this fire door test video,, how quickly smoke and hot gases spread when there are no intumescent seals fitted.

5. 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.

Mann McGowan tell us, “As an intumescent door seal starts expanding from approximately 180°C, a fire seal incorporating either brush or thermoplastic fins (or a fire-only seal used in conjunction with a perimeter seal surface…) is required as a cold smoke barrier…”11

Their use on fire curtains is more problematic, but there are two reasons why some older designs of fire curtain use 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: as we started with, the smoke test BS EN 1634-3 is only performed at cold or ambient temperatures.

The polypropylene material from which the cold smoke seals are manufactured loses its structural integrity before reaching its melting point. It also auto-ignites8 as the temperature rises. This can occur with the temperature as low as 201°C according to Taylor Edge9, posing the additional risk of spontaneous flaming on the non-fire side of the curtain, even without any ignition source.

It is clear, therefore, that while cold smoke seals comply with current test standards, using them on their own is dangerous if anything more than a couple of minutes smoke control performance is required in all fire situations.

6. Is there a smoke control solution for fire curtains that works in a fire?

A better design of smoke sealing on fire curtains is available as shown in Fig. 4.

This design is simple but was also described as ‘genius’ by visitors to Firex and The Fire Safety Event.

Whilst BS EN 1634-3 does not yet call for it to be tested to hot smoke conditions to replicate a fire, the design does only use fire resistant components. 

For example, the same fire resistant fabric that is used for the curtain is used to provide the smoke sealing. This fabric is tested for fire resistance under BS EN 1634-1 which tests to temperatures exceeding 1000°C as shown in Fig. 2.

It is secured to the inside faces of the side guides and headbox using steel brackets and stainless-steel rivets, components with a melting point of between 1350°C and 1530°C.

The proprietary Adexon fire resistant fabric is stiff enough not to yield so as to form a tight seal, as well as being sufficiently flexible to allow smooth unhindered operation of the fire curtain. 

By only using materials that can withstand fire temperatures, this design provides greater peace-of-mind in a fire when compared with traditional older designs that still use combustible cold smoke seals.

As well as being fully legally compliant and third party certified to all the relevant tests and standards, this design offers buyers and specifiers a tangibly better option.

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.

This article was written in October 2022 by the team at Adexon Fire & Smoke and revised on 8th June 2023. It includes the views of the Adexon team and its intention is to raise awareness and standards in the fire safety industry.

If you have a question for the team or would like to give feedback on this article or find out more, please get in touch.

7. References