FSEU Q&A on smoke toxicity

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FSEU Q&A on smoke toxicity

Q1 – What is smoke?

Smoke is a gas phase effluent consisting of solid particles, liquid droplets, gases and vapours.

Q2 – Why is it important to talk about smoke?

The latest fire statistics* from the UK show that of the people who died in fires in UK form April 2013 to March 2014:

  • 41% were killed by gas, smoke and toxic fumes alone.
  • Another 20% were killed by a combination of smoke and burns. Most likely, for those 20%, the smoke had prevented them from escaping leading to severe burns.

* The following figure is from DCLG; Fire Statistics: Great Britain April 2013 to March 2014.

 Q3 – What is hazard?

Hazard is a situation that poses a level of threat to life, health, property, or environment. Most hazards are dormant or potential, with only a theoretical risk of harm; however, once a hazard becomes “active”, it can create an emergency situation.

A hazardous situation that has come to pass is called an incident.

Hazard and probability interact together to create risk.

* http://en.wikipedia.org/wiki/Hazard

Q4 – What influences smoke production?

The amount of smoke produced in a fire depends on the materials burning, the temperature and most important the ventilation conditions (= the amount of oxygen available for the combustion process).

If a fire is allowed to burn clean, it will produce only Carbon Dioxide and water. As the fire intensifies and uses up some of the available oxygen the combustion, process will become incomplete and more gases etc. are produced. The toxicity of the smoke produced changes during the fire and can be summarised in the following table:

1 Gas phase inhibitor is a flame-retardant that changes a products fire performance by inhibiting complete combustion. 

2 Flashover is the time in a fire where a fire changes from a local fire in part of a room to involve the entire room. After Flashover, the entire room will be involved in the fire, the temperature will be above 600 C and flames and smoke are pouring out of the room to other parts of the building or out through windows.

Q5 – How does smoke influence escape time?

There are 3 basic ways that smoke can influence escape time:

  1. The visibility is reduced, making it difficult to see the exit. In addition, many people will not run through a smoke filled corridor even for a short distance.
  2. The smoke will irritate your eyes, nose and throat, making you cough and gasp for air and your eyes will water. This will slow the progress of escape.
  3. The most dangerous part of smoke are the asphyxiant gases. After exposure, the victim will initially lose consciousness (sometimes extremely rapidly – in less than 3 breaths) followed by death unless rescue occurs in time.

There are 3 basic scenarios to consider understanding how smoke can influence escape time:

  1. People are in the same room as where the fire originates. If awake and unimpaired, they will simply leave the room. Construction products with good fire performance and low smoke hazard will increase the time available for people to leave the room. However, the fire and smoke in the room at this stage will be mostly governed by the content (furniture, bedding, decorations, etc.)
  2. People are in a room adjacent to the corridor or pathway where the fire is developing and unaware of the fire. Safe escape for the people in the adjacent room depends on how much smoke and how high the temperatures are in their escape pathway. Construction products with good fire performance and low smoke hazard will increase the time available for people to escape by slowing the fire growth and limit the amount of toxic gases.
  3. People are unaware of a fire in another part of the building until the fire in the room of origin has involved the entire room. At that point in time, smoke is spread rapidly to the rest of the building. The construction products in the room of origin will be involved in the fire adding to the toxic smoke hazard already present from the content. Construction products with no smoke hazard will not add to the amount of smoke spread to the building.

Q6 – Why are construction products important when it comes to smoke toxicity?

When a fire starts, it is most often in the contents of the building such as furniture. The fire will then spread to other parts of the room including the walls and ceiling. Within 3 – 5 minutes (depending on the size of the room) the entire room will be involved in the fire and the construction products within the walls and ceiling will start contributing to the fire and smoke production. So, in medium to large size buildings where escape time for all occupants is at least 5 minutes the construction products can contribute a significant amount of toxic gases leading to a shorter available escape time for the occupants of the rest of the building.

Q7 – But people can only die once in a fire so if the room is fully involved anyone in there is already dead! So why should we care about the smoke?

It is correct that people who do not evacuate the room where the fire originated (due to sleep, substance abuse, invalidity etc.) will die from asphyxiation and eventually the high temperature. However, the more serious case is when smoke + fumes from the developed fire (involving both content and structure) spread to other parts of the building inhibiting the evacuation. The consequence is victim incapacitation followed by asphyxiation.

How many people will die in the fire depends also on how much smoke is spread to the rest of the building. And if the construction products add to the amount of smoke released, then the escape time of other building occupants will be shorter leading to the risk of more deaths.

Q8 – How can we deal with smoke toxicity?

ISO has developed methodologies to measure toxic smoke in fire tests as well as calculating the hazard from the smoke. These principles should be adopted by The European Committee for Standardisation (CEN).

Q9 – Why are construction materials not yet tested for smoke toxicity?

Because smoke toxicity is a complex issue and the methodologies to correctly measure and quantify the hazard from smoke has only recently become available. Some experts believe that the smoke from the content alone is enough to kill the occupants so it is not necessary to be concerned about the smoke from the construction products. This is a strange argument that does not hold true for large buildings where many people have to escape over long distances. Considering that regulators wanted to include the visibility of smoke in the existing test methods, shows that smoke from construction products does matter.

Q10 – Why do you advocate the need for other tests to do the toxic smoke measurements?

As explained in Q4 smoke toxicity changes significantly as the fire develops from initial ignition to fully developed fire in a room. The test therefore needs to be able to cover these different stages of the fire in order to provide all the information needed to evaluate construction product smoke emission during fire

A possible test for this is the large-scale reference test used for the Euroclasses (ISO 9705), as it is a test that can extend into the fully developed stage of the fire.

We do prefer to use small-scale tests when possible and several tests under development in ISO (ISO TS 19700 and the vitiated cone calorimeter) look promising. However, we believe that a first step is to link the behaviour in the small-scale test to that in larger scale to ensure that what we test and classify is related to real life risk. 

Q11 – Can smoke toxicity measurement be incorporated into the already existing harmonised fire tests for CE marking?

Smoke toxicity is a complicated issue as it changes as the fire changes (see Q4). The existing harmonised fire tests only covers the beginning of the fire where there are plenty of oxygen available for the combustion. They do not cover the part of the fire after full room involvement when the amount of oxygen available is limited. So adding smoke toxicity measurements to the existing harmonised tests would only provide part of the information needed for construction products. It is therefore not enough just to add smoke toxicity measurements to the harmonised tests, a test covering the smoke production in the fully developed fire is also needed. For more combustible products exhibiting fully developed fire in the reference scenario, additional consideration is needed.

Q12 – Are all smoke toxic?

Yes! But whether it will be a hazard depends on how much of it is in the air that you breathe. Every combustion reaction produces smoke that is toxic and in sufficiently high concentrations may present hazardous conditions to exposed humans. Short-term hazards are impaired vision due to smoke obscuration and eye irritation, irritation of the upper and/or lower respiratory tracts and narcosis due to the inhalation of asphyxiant gases. These effects, often occurring simultaneously in a fire, contribute to loss of mental acuity and motor coordination, disorientation, panic and eventually physical incapacity.

Q13 – What kills in a fire? Smoke or flames?

Both can be killers but according to statistics more people die from smoke inhalation alone than die from burns alone (see Q2).

Q14 – Which smoke detector should I choose?

One that works! The important thing is to ensure it is functioning. For large buildings, it is also important that they are connected so that people far away from the fire are alerted to the fire as soon as it happens.

Q15 – Is white smoke less toxic than a black smoke?

Not necessarily – see Q16.

Q16 – Can smoke have different colours and if so does it gives an indication of toxicity?

Yes, smoke can have different colours but the colour is not linked in any way to the toxicity. Carbon monoxide and Hydrogen Cyanide are the two primary killer gasses in fires and both are invisible and more or less odourless. The colour of the smoke is due to unburned particles and soot.

Q17 – How fast does smoke spread?

It depends on the layout of the building.

Q18 – How long can I stay in smoke before I am rescued?

It depends on the smoke composition. The more toxic gases in the smoke the shorter time one can stay in it before being seriously injured or dead.

Q19 – Why do people die from inhaling smoke?

Death most often occurs due to asphyxiation.

Q20 – Can smoke burn?

Yes! Fire Fighters often refer to smoke as fuel! Smoke is unburned particles that if there is a high enough concentration, heat and oxygen can burn or even explode. A backdraft is a smoke gas explosion.

Q21 – Is smoke hot? Can it burn you?

Yes! Your airways are even more sensitive to temperature than your skin so hot gases will burn your mouth, nose, airways and lungs.

Q22 – How to survive from smoke?

Wear protective equipment or get out from it quickly. Covering your mouth and nose will keep out some of the particles and lessen the irritations but will not prevent the asphyxiant gases from reaching you.

Q23 – Why does smoke kill when you sleep?

Because you don’t notice that you are slowly suffocated. Some people do wake up from the smell of smoke but not all do.

Q24 – Is all smoke the same?

No. Although all organic materials will produce smoke when they burn, the quantity and composition of smoke is dependent on material including additive type as well as ventilation conditions. For example, polyurethane foam will quickly produce very toxic hydrogen cyanide gas, polystyrene will yield significant quantities of carbon monoxide while PVC yields both carbon monoxide and hydrochloric acid which is recognised as a severe irritant. It should be noted that by means of material/additive selection, products can be designed that offer a low generation of smoke and reduced smoke toxicity without compromising end use performance.

The type of material including additives used in the product needs to be considered, but in addition and more importantly design and end use application cannot be ignored. When it comes to fire safety, proper risk assessment must be undertaken on the final end use application in order to ensure people safety and minimise the risk of fire hazard. In order to fill the gap between performance and safety, regulations, standards and/or guidelines need to also address properly smoke toxicity.  It should also mean that smoke hazard would be part of the building classification.  We believe that cost, safety and environmental matters must be balanced in our society.