Prevention of fires and explosions

Fire can occur when flammable material, oxygen and sufficient ignition energy are available. Explosion depends on an atmosphere of a mixture of flammable material with oxygen. The best approach to prevent fires and explosions is to substitute or minimise the use of flammable material. If that is not possible it is important to avoid effective sources of ignition. The manufacturing, processing or storage of explosives is not covered in this article.

According to the International Association for the Study of Insurance Economics the direct costs of fires and explosions range between 0.07 and 0.26 percent of the Gross Domestic Product and the number of fire deaths varies between 20 in Slovenia and 660 in France, according to figures from 2005^[1].

Fires and explosions in industrial structures and plants may not only lead to losses and damages but may also hamper the functioning of the economy. In Germany three explosions occur daily on average according to the accident insurance company for the chemical industry and similar sectors, whereby fortunately most of them do not cause bigger problems due to protective measures being in place^[2]. Small workshops like garages have a high risk of fires and explosions because they use highly volatile hydrocarbons for spray painting and cleaning purposes. In Schleswig-Holstein (Germany) alone four garages experienced large fires between 2009 and 2010 and one had to close down afterwards.

See also: Accidents and incidents

Fire is a rapid oxidation of material releasing heat, light and various chemical products. The fire triangle describes the conditions that have to be met in order a fire can start: (1) flammable material, (2) oxygen, (3) energy to ignite the fire.

All material capable of an exothermic oxidation reaction has to be considered as flammable. This can be:

• gases such as butane, propane, methane, carbon monoxide, hydrogen,
• liquids such as fuels, solvents, oils, greases, paints and thinners,
• solids such as wood, coal, plastics, metals, food.

Oxygen is usually available in sufficient quantities in our air to get a fire started and to sustain it. Fires may however start much easier and may be more powerful in terms of flame volume and released energy, if the oxygen content of the surrounding atmosphere is increased, e.g. when an oxygen cylinder leaks or bursts or when oxygen releasing substances (e.g. peroxides) are present.

The needed ignition energy can be very low (usually with gases) and can be quite high, which is usually the case with solids. Liquids are often somewhere in between. However the ignition of solids or aerosols depends also on the particle size: fine dusts of e.g. aluminium or flour mixed with air can explode easily.

An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave ^[3]. Does the created shock wave exceed the velocity of sound we talk about a detonation; is the velocity lower the term deflagration is used^[4].

Employers have a duty to ensure the safety and health of workers in every aspect related to the work and they have to provide the necessary organisation and means. Starting with allocating responsibilities the health and safety personnel has to have the necessary knowledge to conduct a risk assessment regarding possible fire and explosion hazards and to select related measures. If appropriately qualified staff is not available within the company, the employer has to contract an outside expert^[5].

On determining the company processes, fire risks as well as fire prevention and fighting measures have to be considered already in the design phase. In collaboration with architects and fire prevention experts this may include: indicating fire compartments, separation of special units, extinguisher systems and escape routes.

Ensuring qualification and further education of all employees involved in fire prevention and fire-fighting tasks is another important management issue. This has to include regular fire drills and should also involve demonstrations of how easily fires can develop presented by the fire brigade or related institutions. Employees should be given the opportunity to not only develop their knowledge but to also bring in their experience. This is all the more important as also unplanned and unforeseeable dangerous situations and the behaviour of workers need to be considered. However in this aspect it is also of foremost importance that all superiors set a good example and always follow the rules themselves.

Good management should also seek advice from outside experts where necessary, provide for effective monitoring, allow opportunities to learn from experience by analysing fires and risky situations and thus create continuous improvement processes. Finally all important aspects should be documented for further reference. In order to have a comprehensive structure, employers should consider to implement an OSH management system, this could even be integrated into a quality and environment management system so as to make use of synergy effects.

In case of higher risks it may be necessary to put a permission system in place, only giving specifically trained people access to sensitive and dangerous areas. Coordinating panels involving e.g. contractors on the premises have to be set up and means and ways of communication between all stakeholders need to be established carefully.

The situation in small and medium enterprises can be quite different from that of larger firms. These may be service companies doing e.g. maintenance work for larger companies or individual customers (e.g. garages). From their point of view it is important to have always the right contact persons, to be involved in the client’s risk assessment processes, to be always up to date regarding developments of the contractor’s buildings and machines, to have the right equipment and to receive sufficient training.

Companies have to conduct risk assessments. A risk assessment is a careful examination of what, in any institution, could cause harm to people, so that one can judge whether there are enough precautions in place or more is needed to prevent harm. It involves identifying the hazards present in any undertaking (whether arising from work activities or from other factors, e.g. the layout of the premises) and then evaluating the extent of the risks involved, taking into account existing precautions^[6].

Fire

A fire hazard can harm workers and the public not only by causing burns but also by heat, fire gases, smoke and weakening structures and it may cause explosions if explosive atmospheres can develop.

Of foremost importance regarding any fire and explosion risk assessment, is to identify related problematic substances in the company. These could be flammable liquids, gases, aerosols, solids, dusts, substances that can develop spontaneous ignition (e.g. textiles with decomposing greases and fats), substances that develop flammable gases on contact with water or other chemicals, explosives, oxidising substances (e.g. peroxides). It has also to be established as to whether there are any working processes that may release any of the above mentioned substances (e.g. dusts, mixture of chemicals). For all the identified substances all relevant parameters, like flash points, vapour pressure, calorific value, explosion limits, etc. should be established.

It is also necessary to clarify, who is working with these substances, in which processes for how long. Not only the normal work procedures have to be analysed but also servicing, test runs, malfunctioning of machines and plants as well as unauthorized access.

Are there effective ignition sources like open flames and high temperatures available or may they develop during work processes? Such ignition sources can be:

• Thermal energy: combustion engines, open fire, hot surfaces, welding sputters, laser
• Electric energy: short circuits, electric arcs, electromagnetic radiation, lightning, electrostatic, heat developed by currents
• Mechanical energy: friction, ultrasound, compression, sparks from tools, grinding
• Chemical energy: spontaneous heating or igniting, catalytic reactions, accelerating exothermal reactions

On having gathered and analysed all relevant information, the risk assessment team has to evaluate the extent of the risks involved. A high risk is indicated by larger amounts of flammable or oxidising substances and by a certain probability of a fire outbreak whereby a fast spread of the fire or big amounts of smoke and heat can be expected. This may be the case for sectors like: petro chemistry, chemical industry, electroplating, light metal processing, printing industry, rubber industry, wood processing, mills and silos, garages, food industry.

Explosion

If problematic substances, as specified in the preceding chapter, exist in the company, the employer has to establish as to whether the development of an explosive atmosphere is possible. Such an atmosphere is defined as a mixture of oxygen with flammable substances, whereby this can include not only gases or aerosols from liquids but also particles from solid matter. For example a cloud of dust from flour or other biologic material, as well as from metal fines, can also explode and cause severe damage^[7]. In the next step it has to be established if this atmosphere can develop in such amounts that it would need special measures.

Results

The risk assessment has also to consider the organisation of the company, any individuals identified as being particularly at risk and the fire or explosion measures already in place. It has to be concluded whether these measures are sufficient or would need changes and improvements. The implementation may mean making changes to the organisation and working procedures, working environment, equipment and products used; training management and staff; and improving communications. The findings have to be recorded.

The adoption of any policies and measures should always be carefully planned, and carried out with consultation of the workforce and their representatives as a key component of success. This should include coordination and communication between contractor and possible service company personnel. The general principle, also laid down in the resp. EU directives, is that risks should be prevented at source and that work organisation, tasks, equipment and tools should be adapted to workers in order to eliminate and reduce risks. Measures should follow the prevention hierarchy:

1. elimination of risks
2. substitution e.g. of dangerous and flammable substances
3. collective control measures like avoidance of effective ignition sources
4. individual control like personal protective equipment

There have to be periodic reviews to check that measures, policies and procedures remain appropriate and are working. They have to be revised if necessary.

The following table shows some possible preventive measures.

Preventive measures regarding explosions

These measures would firstly have to focus on the avoidance of explosive atmospheres mainly by substituting or reducing flammable and oxidising substances (see table 1). Also mixtures with inert gases can sometimes be applied for dilution. If that is not possible, the employer has to assign special clearly marked and cordoned off zones (see table below) according to the ATEX directives^[8][9]. “An international standard, BS EN 60079/10, explains the basic principles of area classification for gases and vapours, and its equivalent for dusts was published in 2002 as BS EN 61241/3."^[10]. After assigning and indicating the zones, the next step is to ensure that effective ignition sources are avoided by using specified equipment/machines for the different zones. Equipment is categorised in 1, 2 or 3 depending on the zone number where it is intended to be used (0/20, 1/21, 2/22).

If it is still not possible to effectively prevent the ignition of the explosive atmospheres, the employer has to introduce constructive measures that limit the effects of explosions to a harmless level. These measures can be: explosion-resistant construction, explosion venting (e.g. bursting discs), explosion suppression (rapid injection of extinguishing agents) or explosion isolation.

All these steps have to be documented, put into an explosion protection document and shown to the authorities on demand.

Measures in case of an accident

Especially the large fires and explosions in firms (e.g. explosions in a chemical company in Rotterdam in early 2011) indicate how important it is to have safe systems in place. On the other hand it also shows that it is equally important to be prepared when accidents happen. Such plans should consist of a first aid organisation, of fire fighting and evacuation plans and of related alarm plans. This should be established based on the company’s risk assessment and involve appropriately qualified staff or consultants. Exercises should be conducted regularly.

On the basis of the "Framework directive" a series of individual directives were adopted, especially relevant for this topic are the following:

• Directive 1999/92/EC – risks from explosive atmospheres of 16 December 1999 on minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres (15th individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC^[11].
• Directive 92/58/EEC – safety and/or health signs of 24 June 1992 on the minimum requirements for the provision of safety and/or health signs at work (ninth individual Directive within the meaning of Article 16 (1) of Directive 89/391/EEC)
• Directive 98/24/EC – risks related to chemical agents at work of 7 April 1998 on the protection of the health and safety of workers from the risks related to chemical agents at work (fourteenth individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC)

These directives including the framework directive had to be transformed into the national legislation of the member states.

There are two so called ATEX directives, one for the manufacturer and one for the user of the equipment: the ATEX 95 equipment directive 94/9/EC, Equipment and protective systems intended for use in potentially explosive atmospheres and the ATEX 137 workplace directive 99/92/EC, Minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres.