This Directive shall apply to electrical equipment for use in a potentially explosive atmosphere which employs one or more of the following types of protection:
- oil immersion 'o',
- pressurized apparatus 'p'
- powder filling 'q',
- flameproof enclosure 'd',
- increased safety 'e',
- intrinsic safety 'i'.
The different techniques lend themselves to different applications and, for instrumentation used in process measurement and control, the two leading techniques are the use of 'flameproof enclosures' and 'intrinsic safety'. With the flameproof technique, known as 'explosionproof' in the USA and Canada, hazardous-area equipment is surrounded by a strong enclosure which can withstand internal explosions without igniting the external atmosphere. This technique, which has been in use for over 80 years, allows high power levels but has the disadvantages that the enclosures are heavy and expensive and must not be opened without first disconnecting the electrical circuit or obtaining a 'gas-free certificate' for the relevant plant area.
