(17a) A Practical (Semi Quantitative) Tool for the Determination of Dust Explosion Risks for Workers in Industry

Employers in industries dealing with flammable dusts wants to protect their workers against dust explosion hazard. Because of legalization and guidelines in this field the risks have to be assessed so that adequate measures can be taken to reduce the risk to a tolerable level.

As a result of the implementation of the European guideline 1999/92/EC into the national legalization of the European Union member states, employers of many companies with a dust explosion hazard want to assess and evaluate the risks in a systematic way. Furthermore these employers have to describe these activities in a mandatory explosion protection document and have to update this document continuously.

The need for practical instruments to assess and evaluate these risks in industry is increasing but practical instruments are rare. Because of this, TNO develops a software tool by which, on the basis of a limited amount of data, the risks in industry can be assessed in a semi quantitative way.

In compliance with article 4 of the ATEX guideline 1999/92/EC the employer shall assess the specific risks arising from explosive atmospheres, taking account at least of:

-the likelihood that explosive atmospheres will occur and their persistence; -the likelihood that ignition sources will be present and become active and effective; -the installations, substances used, processes, and their possible interactions; -the scale of the anticipated explosion effects.

The risks are classified in risks levels, the determination of which is based on the above mentioned aspects. Harmful primary effects of dust explosions like the blast (pressure wave), flames and projectiles, but also secondary effects, like collapsing of constructions are estimated and translated to consequences for the workers involved. The probability of occurrence for an explosion in each of the process parts is estimated based on the hazardous area classification (zoning), the presence of potential ignition sources and a ignition risk assessment. For this risk assessment the properties of the product and the process conditions are taken into account.

Required data by means of a checklist analysis is collected by a plant visit, interviews, questionnaires and evaluation of technical documentation. With this tool the risks for all relevant apparatus and process parts are determined. In this way the risk for each apparatus and process part the contribution to the risk for the workers involved is made clear. Both technical and organizational preventive measures, but also explosion protective measures, are considered.

With this tool it is possible to get insight how the risk related to a specific item can be reduced and to what extent. This instrument can contribute to efficiently assessing and evaluating dust explosion risks and can help employers to take the right priorities for technical or organizational measures in order to reduce the risks for the workers most effectively.