RISK ASSESSMENT FOR EQUIPMENT USED IN EXPLOSIVE ATMOSPHERES (ATEX)

EN ISO 14121-1- principles of risk assessment - is the Harmonised European Standard that is to be used for ATEX Equipment .

EN 1127-1 - Concepts & Methodology of Explosion Prevention and Detection - defines what should be included in a Risk Assessment for Equipment used in Explosive Atmospheres.

The standards do not supply methods for analysing or assessing risks but provides guidance on the elements to be included. For detailed methods contact: David Baker

The risk assessment should consider all phases of life of the equipment, the possibility of circumventing safety measures, misuse and emergencies such as power failure. It should cover hazards to operators, trainees, domestic animals and the general public as well as hazards to material or the environment.

Annex A to EN ISO 14121-1 and EN 1127-1 provide useful examples of hazards to be taken into account , but the risk assessor should also consider all the hazards peculiar to the particular machinery or equipment .

The Risk assessment is to be documented demonstrating the procedure and the results.

Remember that EN 1127-1 requires that risks should be eliminated or minimised using three principles:

• Prevention by avoiding explosive atmospheres
• Prevent by avoiding effective ignition sources
• Protection by limiting the effects of explosions

Explosive Properties of Substances

Consider dusts as well as flammable substances. To determine the hazard consider:

• Combustion Properties e.g.
  • Flash point
  • Lower and Upper Explosive Limits (LEL or LEL)
  • Limiting oxygen concentration ( LOC)

• Ignition Requirements e.g.
  • Minimum energy
  • Minimum temperature
  For ignition of an explosive atmosphere or a dust layer

• The Explosion e.g.
  • Maximum pressure
  • Maximum rate of pressure rise, etc
  This hazard assessment requires expert knowledge.

The Likelihood of a Hazardous Explosive Atmosphere

Consider chemical or biological reactions and pyrolysis. A hazardous explosive atmosphere depends on:

• The degree of dispersion of the flammable substance
• Concentration in air
• Amount sufficient to cause injury or damage

A hazardous explosive atmosphere should be assumed unless proven otherwise.

See EN 1127-1:2007 for more information

Ignition Sources

Consider sources that occur:

• Continuously or frequently during normal operation
• In rare situations as a result of malfunctions
• In very rare situations as a result of rare malfunctions

Consider all sources e.g. hot surfaces, flames, hot particles, sparks ( electrical & mechanical), electro-static discharges, lightning, electro-magnetic effects, ultrasonic compression, heat- generating reactions etc.

Explosive Effects

Consider:

• Fire from flames
• Thermal radiation
• Pressure waves
• Flying debris
• Hazardous materials

In the specific cases occurring in the particular machinery, plant or environment.

Note: Read the standards for precise wording and for additional information contact :

David Baker

For further information and free advice please complete our form

tel: +44 (0) 1380 848170      fax: +44 (0) 1380 840152      david.baker@riskman.info