Tag Archives: firefighting

Permanent oxygen reduction provides effective fire protection

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A standard is on the way which will make permanent oxygen reduction an effective alternative to sprinkling in Denmark. The Danish Working Environment Authority has no objections in principle.

In future, it may be easier to fireproof, for example, high bay warehouses and storerooms in museums – and, at the same time, reduce the risk of damage caused by sprinkling. This is because plans for a forthcoming European standard for the design of systems for permanent oxygen reduction are due to be passed in 2016 and issued in 2017.

The forthcoming standard is called EN 16750 Fixed firefighting systems — Oxygen reduction systems — Design, installation, planning and maintenance. It has been drawn up by the European standard organisation, CEN, in a working group set up under CEN/TC 191/WG6 with the participation of fire technology consultant Rolf Knudsen from DBI.

– Permanent oxygen reduction is an alternative to extinguishing fires by means of, for example, sprinkling, where there is otherwise a need for a sprinkler more or less above every pallet at all levels. With a permanent oxygen reduction system you can fireproof the whole warehouse more easily and, at the same time, avoid the often costly water damage that is caused when a sprinkler system has been activated, explains Rolf Knudsen.

The working environment
The reduced oxygen concentrations do not exclude people from working in the buildings – provided, of course, that a number of safety requirements are complied with.

– There are no immediate physiological problems with being in a room with an oxygen concentration of, say, 15%, if you are otherwise fit and healthy and do not need to perform any physically hard work for long periods, insists Rolf Knudsen.

In fact, many people have experienced an equally low oxygen concentration when they have been on an aeroplane. The air in the pressurised cabin is equivalent to air with an oxygen concentration of around 15.5% volume on the ground. This is the same as being approximately 2,400 metres above sea level.

– In both the UK and Germany there are rules governing how long you may work in reduced oxygen conditions, says Rolf Knudsen.

More extreme proof is provided by cyclists, who prove that it is even possible to perform extremely hard physical work in conditions with low concentrations of oxygen. What Tour de France cyclists have to endure in, for example, L’Alpe d’Huez, is not just down to the steep mountain roads, but is also due to the fact the oxygen levels in the ‘thin air’ at 3,300 metres is equivalent to an oxygen concentration of just 13.8% volume on the ground.

Green light from the Danish Working Environment Authority
The Danish Working Environment Authority has no objections in principle to permanent oxygen reduction as a means of fireproofing.

– We are positively disposed towards the principle if various criteria and limits are complied with in relation to work safety. Here, we will work on the basis of the Germany safety requirements outlined in BGI/GUV-I 5162, drawn up by the German Institute for Work and Health (DGUV) with information on working in oxygen-reduced atmospheres, explains Erik Lund Lauridsen from the Danish Working Environment Authority.

The German regulation has, for example, four fire classifications for different oxygen concentrations. In Class 0, the oxygen concentration is above 17. Here, the only safety requirement is that employees have to undergo special instruction.

In Class 1 (17.0 % vol. – 15% vol.) employees also have to undergo an occupational health examination to exclude the presence of, for example, heart disease or other risks. In addition, there is a requirement for a half-hour break to be taken in a ‘normal’ atmosphere after four hours of work.

I Class 2 (15.0 %. vol. – 13.0 % vol.) the requirements are the same, the only difference being that the break has to be taken after two hours’ work. In Class 3, with an oxygen concentration of below 13% vol., it is forbidden to be in the room without special measures being in place.

– In addition, there are a number of requirements relating to the actual systems. For example, both the measurement and control of oxygen concentration must be reliable and there must be assurances that the oxygen concentration is not able to fall too low by mistake. This requires the use of approved equipment and regular inspections, stresses Erik Lund Lauridsen.

Likewise, it must be ensured that the oxygen-reduced atmosphere cannot spread to other rooms in the building.

Classic fire theory
The principle of oxygen reduction is based on the classic ‘fire triangle’ whereby the prerequisites for a fire are heat, oxygen and flammable material. In other words, this means that you must permanently maintain an atmosphere in which the stored material cannot burn.

Ordinary air contains approximately 21 % vol. oxygen, which can fuel a fire, but if the oxygen content is reduced to, for example, 15% vol., a flaming fire is not possible for materials such as wood, cardboard and several types of plaster. From the 15% vol. a number safety and sensor tolerances have to be subtracted, and for that reason the required oxygen concentration will be approximately 2% vol. less than the required ignition limits for the material that is to be protected.

The oxygen is reduced by adding extra nitrogen to the air in the protected building, which previously amounted to approximately 80% vol. of atmospheric air. This can be done by either blowing pure nitrogen or a mixture of nitrogen/air into the building, which by its very nature must be relatively air-tight.

– The standard will include rules relating to the design of oxygen reduction systems. For example, you can find tables specifying the maximum permitted oxygen concentration based on the materials that are to be protected, explains Rolf Knudsen.

In the case of more specialized materials, the standard refers to how it is possible to find the maximum oxygen concentration by means of a test.

Fireproofing by means of permanent oxygen reduction is already used to some extent in, for example, Germany, the UK, Spain, Switzerland and Norway for fireproofing warehouses, freezer rooms and server rooms.

Flashing signs lead to quicker evacuation

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When evacuation signs start flashing, evacuation takes place more quickly and is more evenly distributed. This has been demonstrated by studies from abroad. And new technology also reduces the big unknown in every evacuation: the response time.

Example: A fire breaks out in an airport terminal. The detection system senses the fire at once and the evacuation signs automatically start to flash. The public address system asks all travellers to leave the terminal via the evacuation routes. However, not all the evacuation signs flash green. Instead, some have a flashing red cross at the top. This is because the fire detection system has registered that the fire has broken out near two of the evacuation routes. And so, to divert the public away from the risk zone, the signs above these evacuation routes flash with a red cross.

Another example: A shopping centre is attacked by armed terrorists. Using fire detection systems, dynamic signage, public address warnings, evacuation simulation programs and video cameras, the shopping centre’s safety officers are able to guide customers and other civilians away from the terrorists and out of the centre, without running into the terrorists’ guns.

Flashing signs tell you to choose a different route
These are imaginary examples, but could easily become reality if the various fire fighting systems were linked together. This is something currently being researched in other countries, for instance in EU-financed projects. These have investigated the effect on evacuation of dynamic evacuation signs – in other words, where the signs flash when the alarm goes off, with a red cross over them if the public needs to choose a different route.

– Experiments show that the public will evacuate more quickly than usual with the dynamic signs, says Lise Olesen, a fire safety consultant at the Danish Institute of Fire and Security Technology (DBI). She continues:

– This isn’t a technology we have seen much of in Denmark. But it could easily be of benefit for evacuating airports or conference halls, where many people are gathered together and are unfamiliar with the escape routes. The same goes for night clubs, where it can be difficult to find your way out and where it is hard to attract people’s attention.

Both the above examples would be possible if the technology was fully implemented and all systems were able to communicate. But complete linkage of all systems is unnecessary for achieving quicker and better evacuation. If just the fire safety systems and the lighting on the evacuation routes lighting can communicate, so that signs will flash when the alarm goes off, this can have a positive effect.

Bringing down response time
Many people don’t notice evacuation signs. Even if we are familiar with the green signs with the stylised icon of a man running towards a door, few people notice them in daily life. We become blind to them – even, unfortunately, when disaster strikes.

– The majority of people will try to escape the same way they came in, without much noticing what the signs say. But if the signs are actually flashing, they attract our attention, and this can lead both to quicker evacuation and less congestion at the main entrance, where most people will typically try to exit, Olesen says.

The flashing sign can also help to bring down the response time – which means the time from when the alarm goes off to when the public start to evacuate the building. Sometimes this can take a considerable period of time.

– When the alarm goes off, there are a number of factors which affect how long people take before they react. Humans are herd animals, so first of all we look to see how other people are reacting. And if you’ve just been served with a steak, you’ll prefer to sit and finish it. After that, you’ll need to find your jacket, your children, your friends or go to the toilet. That is why the response time is the big unknown in an evacuation situation, and dynamic signage can bring down that time, Olesen maintains.

The technology is out there
In rapidly developing fires, every minute counts, so the effect of linking systems and using dynamic signage can be significant.

– Every reduction in response time can potentially save life, and technology provides a number of opportunities for improving safety. This is true of both advanced and simpler solutions, Olesen explains.

It is still uncertain when or how the technology will become widespread but the possibilities are already with us.

– It’s not a question of technology, because we already have what we need to realise the simple solutions. It’s more a question of getting the different systems to cooperate, Olesen says.