ATEX is the name commonly given to the two European Directives for controlling explosive atmospheres:
The ATEX directive consists of two EU directives describing what equipment and work environment is allowed in an environment with an explosive atmosphere. ATEX derives its name from the French title of the 94/9/EC directive: Appareils destinés à être utilisés en ATmosphères EXplosives.
Ever since the introduction of ATEX, CTS management have been heavily involved in auditing existing cereal processing plants. We are able to give initial advise and prepare basis of safety documentation.
Following a basis of safety report either by CTS or your own consultant, we are able to give practical solutions on how to meet the recommendations and supply/install cost effective equipment. A full health and safety file will be prepared for you to present to the H&SE.
CTS have been involved in number of ATEX assessment and upgrade projects. The management team members have in the past worked alongside major consultants Pheonix, Burgoyne, Euratex, Sira, etc and are also well versed with the major explosion protection equipment suppliers such as Fike, Rembe, Stuvex, etc.
CTS not only advise but can also carry out the complete upgrades in line with the recommendations, a long with calculations, supply of specialist explosion protection equipment best suited for the job, installation and commissioning.
The Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) sets minimum requirements for the protection of workers from fire and explosion risks related to dangerous substances and potentially explosive atmospheres in the workplace.
DSEAR is the ‘framework’ adopted by the Health & Safety Executive (HSE) to facilitate compliance to ATEX 137 within the UK. Other European countries will not adhere to DSEAR specifically, however, there will be similar frameworks in place as a vehicle towards ATEX 137 compliance.
Responsibilities and Requirements of DSEAR
It is the responsibility of the employer to minimise the risks to their employees that can result from potentially explosive atmospheres (i.e. where there is presence of gases, vapours, liquids or dusts). DSEAR calls upon several requirements to facilitate this:
- Conduct risk assessments of non-electrical equipment already installed on-site.
- Carry out competent risk assessments on any work activities involving dangerous substances.
- Provide equipment and procedures to deal with accidents and emergencies.
- Provide instruction and training to employees.
- Classify the site into zones of risk (Area Classification).
- Use appropriate (certified) equipment in hazardous areas.
- Co-ordinate site health and safety for all users of the site, including contractors, visitors, staff, etc.
There are recommended publications, which provide guidance:
- EU Project No: SMT4-CT97-2169 The RASE Project. Explosive Atmosphere: Risk Assessment of Unit Operations and Equipment. 17 March 2000.
- DTI – Guidance notes on UK Regulations, First Edition – February 1998. Equipment and protective systems intended for use in potentially explosive atmospheres.
- Safe Handling of combustible dusts. Precautions against explosions’.
Health and Safety series booklet HS(G)103.
- IChemE ‘Guide to Dust Explosion Prevention and Protection Part 1 – Venting’, Geoff Lunn, Second Edition.
“The establishment of a coherent strategy for the prevention of explosions requires that organisational measures complement the technical measures taken at the workplace; Directive 89/391/EEC requires the employer to be in possession of an assessment of the risks to workers’ health and safety at work; this requirement is to be regarded as being specified by this Directive in that it provides that the employer is to draw up an explosion protection document, or set of documents, which satisfies the minimum requirements laid down in this Directive and is to keep it up to date; the explosion protection document includes the identification of the hazards, the evaluation of risks and the definition of the specific measures to be taken to safeguard the health and safety of workers at risk from explosive atmospheres, in accordance with Article 9 of Directive 89/391/EEC; the explosion protection document may be part of the assessment of the risks to health and safety at work required by Article 9 of Directive 89/391/EEC.”
It is important to recognise the factors, which together form a risk of a dust explosion occurring and the likely consequences of such an occurrence.
Firstly, for a dust explosion to occur there has to be a combination of three factors present -Fuel, Oxidising Agent and Ignition source.
The fuel, in grain handling systems, would be cereal dust. In general there has to be a concentration of dust mixed with air in the correct proportions to allow flame propagation. Particle size (below 500m) is also a factor and relates to the speed at which the flame will propagate through the dust cloud. Typically, there has to be in the region of 30 to 60 g/m3 for the lower flammable limit to exist. Heat (or an ignition source of sufficient energy) has then to be introduced.
The nature of the explosion then depends on:
The explosibility of the dust. This is summed up in the form of a constant known as the Explosibility Index = Kst factor. Most grains are generally regarded as an St 1 class of dust i.e. Kst < 200 bar m/s.
The volume of the vessel or surroundings. Large volumes generally produce large explosions. If a vessel is small enough and strong enough then it is possible that an explosion may be contained without catastrophic distortion or rupture of the vessel, however, as cereal dust explosions can reach pressures in the order of 8 bar it is unlikely that containment can be relied upon. An initial explosion in a small vessel may relieve into a surrounding area giving rise to a much larger secondary explosion if sufficient dust is present. This may be by disturbing additional dust deposits within the surroundings therefore good housekeeping within the dry good area is essential.