HAZARDOUS AREA TECHNICAL GUIDE
1. Basics Principles
A hazardous area is defined as an area where the atmosphere may contain quantities of flammable gases or combustible dusts. In this atmosphere, a fire or explosion can happen when the following three components are present at the same time in sufficient proportions. These conditions are often represented by a combustion triangle shown here.
Fuel: flammable gases, vapours, liquids or combustible dusts, fibres or flyings. Examples are methane, hydrogen or coal dust. Oxygen: generally air, but not exclusively from air. As an academic point, the gas acetylene is an exception; it can explode without Oxygen as it produces its own while burning. Heat (ignition energy): may be produced by electrical or thermal sources. Here is a list of possible ignition sources: lightning strikes, open flames like a lit cigarette to welding activity, electric or electrostatic discharges, and adiabatic compression when air is pumped into a vessel and the vessel surface heats up.
Industrial hazards involving explosion risks from gases, vapours and dusts are sometimes not so obvious but can cause catastrophic devastation such as at Flixborough (1974), Piper Alpha (1988) in the North Sea or more recently the Buncefield Oil Storage Depot in Hemel Hempstead (photo on the cover page).
From 30 June 2003, organisations within the EU must comply with the ATEX (ATmosphères EXplosives) directives to protect their employees from explosion risk in areas with explosive atmosphere.
Weighing equipment in use before July 2003 is allowed to be used indefinitely provided a risk assessment shows it is safe to do so. However, if that equipment is refurbished or upgraded so that its original specification is changed, it will have to be made to comply with the full requirements of the Directive.
There are two ATEX directives (one for the equipment manufacturer and one for the user of the equipment):
the ATEX 95 equipment directive 94/9/EC (also known as Article 100a and Article 95), Equipment and protective systems intended for use in potentially explosive atmospheres, this directive has been implemented into United Kingdom law by Statutory Instrument (S.I.) 1996:192. the ATEX 137 workplace directive 99/92/EC, Minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres. This directive is implemented in the UK by the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR).
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.
These directives are enforced by the Health and Safety Executive in the UK.
There are some exclusions which are mostly items of equipment where application of the ATEX requirements would lead to conflicts in the application of other directives.
The Directive does not cover:
Medical devices intended for use in a medical environment Equipment and protective systems where the explosion hazard results exclusively from the presence of explosive substances or unstable chemical substances
HAZARDOUS AREA TECHNICAL GUIDE