Explosive atmospheres can be caused by flammable gases, mists or vapours or by combustible dusts. If there is enough of the substance mixed with air, then all it needs is a source of ignition to cause an explosion.
Explosions can cause loss of life and serious injuries as well as significant damage. Preventing releases of dangerous substances which can create explosive atmospheres, and preventing sources of ignition, are two widely used ways of reducing the risk. Using the correct equipment can help greatly in this.
What is an explosive atmosphere?
An explosive atmosphere is defined as a mixture of dangerous substances in the air in the form of gases, vapours, mist or dust, which, under certain conditions of temperature and pressure, has the potential to catch fire and explode.
Where can explosive atmospheres be found?
Many workplaces may contain, or have activities that produce, explosive or potentially explosive atmospheres. Examples include places where work activities create or release flammable gases or vapours, such as vehicle paint spraying, or in workplaces handling fine organic dusts such as grain, flour or wood.
What is ATEX?
ATEX (ATmospheres EXplosibles in French) is the name commonly given to the two European Directives for controlling explosive atmospheres:
1) Directive 1999/92/EC (also known as 'ATEX 153' or the 'ATEX Workplace Directive') on minimum requirements for improving the health and safety protection of workers potentially at risk from explosive atmospheres.
2) Directive 2014/34/EU (also known as 'ATEX 114' or 'the ATEX Equipment Directive') on the approximation of the laws of Members States concerning equipment and protective systems intended for use in potentially explosive atmospheres.
International standards IEC 60079 and IEC61241 (IECEx), which are harmonized with EN European Directives, are the main hazardous area standards recognised throughout the rest of the world, outside of Europe.
Classification of areas where explosive atmospheres may occur
Employers must classify areas where hazardous explosive atmospheres may occur into zones. The classification given to a particular zone, and its size and location, depends on the likelihood of an explosive atmosphere occurring and its persistence if it does.
Possible hazards in potentially explosive atmospheres
When using equipment in a hazardous areas, steps must be taken to ensure all products used are resistant to every type of hazard. These include the following:
- Ignition sources - potential ignition sources such as sparks, flames, electric arcs, high surface temperatures, acoustic energy, optical radiation, electromagnetic waves and other ignition sources
- Static electricity - electrostatic charges capable of resulting in dangerous discharges
- Stray electric and leakage currents - in conductive equipments parts which could result in, for example, the occurence of dangerous corrosion, overheating of surfaces or sparks capable of provoking an ignition
- Overheating - caused by friction or impacts occuring between materials and parts in contact with each other while rotating or through the intrusion of foreign bodies
- Pressure compensation operations - equipment and prtective systems must be designed or fitted with integrated measuring, control and regulation devices to ensure that pressure compensations arising from them do not geneate shock waves or compressions which may cause ignition.
- Power failure - where equipment and protective systems can give rise to the spread of additional risks in the event of a power failure, it must be possible to maintain them in a safe state of operation independently of the rest of the installation
- Connections - equipment and protective systems must be fitted with suitable cable and conduit entries. When equipment and protective systems are intended for use incombination with other equipment and protective systems, the interface must be safe.
Equipment and protective systems must be designed and constructed to be capable of performing their intended funtion safety, even in changing environmental conditions and in the presence of extraneous voltages, humidity, vibrations, contamination and other external effects, taking into account the limits of the operating conditions.
Equipment parts used must be appropriate to the intended mechanical and thermal stress, and capable of withstanding attack by existing or foreseeable aggressive substances.