Explosive atmospheric conditions in the workplace can be very dangerous, leading to significant injuries and perhaps even death. Dangerous workplace atmospheres can be caused by a gathering of flammable gases, mists, vapours, or combustible dusts. If these substances are present in a large enough volume and are then combined with air and an ignition source, an explosion would most likely occur.
It's patently obvious that stopping the release and build-up of dangerous airborne substances and preventing the sources of ignition are the most common ways of reducing the risk of explosion.
The ATEX Directives were designed to help remove trade barriers and establish a cohesive strategy for the prevention of explosions at the workplace within the EU. In parallel with ATEX directives, the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) places a duty on employers to eliminate or control the risks from explosive atmospheres in the workplace.
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What is an explosive atmosphere?
According to the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR), an explosive atmosphere is defined as a mixture of dangerous flammable substances with air under atmospheric conditions, in the form of gases, vapours, mist or dust in which, after ignition has occurred, combustion spreads to the entire unburned mixture.
What is a flammable substance?
A flammable substance includes any product or preparation, which because of its properties or the way it is used, can cause harm to people from explosions and fires.
Typical examples of flammable substance include - petrol, liquefied petroleum gas (LPG), paints, varnishes, solvents, and dust which when mixed with air could cause an explosive atmosphere, such as dust from milling and sanding tasks. Flammable substances can be found in varying quantities in most workplaces.
The ATEX Directives, (ATEX is an abbreviation of ATmospheres EXplosibles) were created to form a common approach to removing trade barriers, and to establish a cohesive strategy for the prevention of explosions at the workplace within the European Economic Area.
The two primary European Directives for controlling explosive atmospheres in the workplace are:
Directive 99/92/EC (also known as ATEX 137 – Workplace Directive) provides the minimum requirements for improving the health and safety protection of workers potentially at risk from explosive atmospheres.
Directive 2014/34/EU (also known as ATEX 114 – Equipment & Protective Systems Directive) refers to the approximation of the laws of Members States concerning equipment and protective systems intended for use in potentially explosive atmospheres.
Where do you find explosive atmospheres?
Countless working environments feature processes that could create explosive or potentially explosive atmospheres. Typical examples include those that create or release flammable gasses, mists, and vapours, such as vehicle paint spraying, or factories handling grain flour or wood where fine organic dust particles are present.
Three elements are required to cause an explosion: Fuel (gas or dust), Oxygen (Air) and an ignition source such as an electric spark, a hot surface or an electrical short-circuit. The risk of an explosion is based on the probability of a fuel and oxygen mixture occurring over a period of time.
The employer needs to take appropriate measures to prevent the formation of explosive atmospheres, or where the nature of the activity doesn’t allow that, the avoidance of the ignition of explosive atmospheres and reduce the effects of an explosion in a way that the health of workers is not at risk.
Employers must classify areas into zones where hazardous explosive atmospheres may occur. These classifications depend on size, location, and its persistence. Hazardous places are classified in terms of zones based on the frequency and duration of the occurrence of an explosive atmosphere.
Hazardous Areas and ATEX Zones
If an explosive atmosphere requires special precautions to protect the safety of workers, it is referred to as a hazardous area. Hazardous areas are classified based on the frequency of occurrence and duration of an explosive atmosphere.
The classification is split further between flammable gases and combustible dusts. For gases the following classification is used:
For dusts, the following classification is utilised:
Explosive atmospheres in the workplace
In the UK, the requirements of Directive 99/92/EC were made effective through regulations 7 & 11 of DSEAR. These apply to workplaces where a potentially explosive atmosphere may occur. Certain sectors and work activities are exempt due to other legislation that is listed in regulation 3 of DSEAR.
How can an explosive or flammable atmosphere be avoided?
Measures should be taken to reduce or eliminate the risk from explosive atmospheres and to mitigate the effects from any fire or explosion.
Elimination
- Replacing a flammable substance with a substance or process that eliminates the risks
Substitution
- Where total elimination is not possible the flammable substance may be replaced with a less hazardous one with perhaps a higher flashpoint
Control measures
- Reduce the quantity of the flammable substance kept to a minimum
- Avoid or reduce releases
- Remove dust deposits
- Control releases at source
- Avoid adverse conditions
- Gas alarms
Mitigation measures to minimise the impact of an explosion or fire
- Prevention of spreading using fireproof materials, fire safety devices
- Reducing the number of employees exposed to a minimum
- Provide plant and equipment that can contain/suppress an explosion, or vent it to a safe place
DSEAR - What does it require?
DSEAR insists employers eliminate or control the risks from dangerous substances - more information can be found in DSEAR. Additional to the general requirements, the regulations place the following duties on employers with workplaces where explosive atmospheres may occur.
Prior to a zoned areas start-up, the employer must ensure that explosion safety measures are safe. A person or organisation trusted to evaluate the risks has to perform this task, along with the adequacy of the explosion control equipment and any further measures.
With new installations verification should be conducted at various stages of the project, including during the design, construction, and commissioning phases. Failure to conduct adequate reviews at each stage will leads to incomplete, inefficient, or inadequate verification processes.
To avoid these mistakes, it is essential to engage experienced and qualified professionals who have specialised knowledge in the field of dangerous substances and explosive atmospheres.
Verification needs to answer 5 points
- What are the hazardous properties and quantities of the dangerous substances used?
- Is the plant, equipment, and protective systems suitable for operating in explosive atmospheres?
- Are work processes, operating procedures, and systems adequate to ensure the safety of personnel?
- Can the intended control measures:
- Prevent the formation of explosive atmospheres
- Control the risks from explosive atmosphere
- Mitigate the effects of an explosion
- Are the emergency arrangements in place adequate?
Demarcation of ATEX Zones
Zoning involves defining parts of a site where explosion risks can occur. These locations are qualified as hazardous zones and delimited based on the relevant degree of danger.
Demarcation of an ATEX zone is a crucial step for the safety of workers in areas where explosive atmospheres can form. ATEX zones defined by the European Directive 1999/92/EC are used to classify work areas based on their level of explosion risk.
The demarcation of an ATEX zone is based on a risk assessment that determines the chances of an explosive atmosphere forming in each area. This assessment considers factors such as the frequency and duration of the presence of explosive substances, ventilation, and potential sources of ignition.
When the risk zones have been identified, they must be clearly marked. Methods may vary depending on circumstances, common options include:
- Zones can be identified by ground markings in different colours for each zone, enhancing boundary identification.
- Signs can be used to indicate the presence of ATEX zones and provide information about specific risks.
- Barriers can be used to separate risk zones from areas where explosion risks are lower.
Use of Specific Equipment: Equipment such as lights, fans, and motors can be designed for specific use in ATEX zones. It's essential to note that the demarcation of ATEX zones must be regularly reassessed based on changes in working conditions and regulations.
Protective system and equipment
Classified zones must be protected from sources of ignition. Equipment and protective systems in these areas should meet the requirements of the Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 1996. This equipment must not be capable of causing ignition, such as not being able to generate electrical sparks, feature hot surfaces that could ignite substances within a given atmosphere and so on.
Equipment in use before July 2003 can continue to be used providing a risk assessment has been undertaken. As both installations and regulations adapt and change the need for continual risk assessments is necessary.
Antistatic clothing
Employers must provide employees in zoned locations with clothing that cannot create electrostatic discharges which could cause ignition, for example – antistatic safety boots and antistatic shirts. The specific clothing required depends on the risks identified during the initial and ongoing risk assessments.
Equipment and protective systems used in explosive atmospheres
Directive 2014/34/EU was created to allow the free trade of ATEX equipment and protective systems within the EU by removing the need for separate testing and documentation for each Member State.
The requirements of the Directive in the UK were put into effect through BIS Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 1996 (SI 1996/192). This applies to equipment intended for use in explosive atmospheres and associated protective systems.
Manufacturers and suppliers (or importers, if manufactured outside the EU) must ensure their products meet H&S requirements and undergo conformity procedures. This can involve testing and certification by a 'third-party' certification body (Notified Body). Manufacturers/suppliers can 'self-certify' equipment intended for use in less hazardous zones. Once certified, the equipment is marked by the 'EX' symbol.
The certifications ensures that the equipment is fit for purpose and that information is supplied with it to ensure it is used safely. BIS has policy responsibility for the Regulations, although HSE enforces them. Regulations and directives are regularly updated and modified – so please make sure that you are up to date with the latest directives and regulations outlined above.
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