Page 328 - Offshore Electrical Engineering Manual

Avoidance of Ignition by Radio and Radar Transmissions 315

SELECTION OF OTHER EQUIPMENT

Much of the explanation above regarding hazardous area motors may be applied to
other hazardous area equipment. Switchgear, being inherently sparking equipment,
must be enclosed in an explosion-proof or pressurised enclosure, as it cannot meet
the criteria for increased safety Ex ‘e’ certification.
Enclosures used for housing cable terminals may be of explosion-proof or
increased safety design.
Common types of enclosure and limitations affecting their use and those for cable
glands and transits are discussed in PART 2 Chapter 8.
Hazardous area lighting is discussed in PART 2 Chapter 14.

AVOIDANCE OF IGNITION BY NON-ELECTRICAL EQUIPMENT
(REFER BS EN ISO 80079-36 & 37)

There are many mechanical devices that operate with high surface temperatures or
generate sparks, when running, or if they have developed a fault. The list below is
not exhaustive:

• reciprocating engine turbo-chargers and exhausts
• gas-turbine casings
• pumps
• gearboxes
• Belt drives and continuously variable transmission (CVT) drives
• fan blades impinging on ducting
• process heaters

All of these devices will need to be risk-assessed at the very least, and mitigating
devices fitted (e.g., spark arresters, water jackets, anti-static belts etc.). It is recom-
mended that alternative equipment be considered if available, which does not need
such protection, since mitigating devices will require critical safety maintenance. CVT
drives are not recommended, because although anti-static belts will prevent static
sparks, the belts are prone to becoming displaced and jammed against the driving pul-
ley, generating a hotspot. It would be possible to pressurise or nitrogen purge the CVT
housing, but an alternative electrical VSD would probably be a simpler solution.

AVOIDANCE OF IGNITION BY RADIO AND RADAR
TRANSMISSIONS (REFER TO PD CLC/TR 50427)

Electromagnetic waves of sufficient power will generate sparks in metallic objects,
as can be experienced with household microwave ovens. Radar and radio transmit-
ters helicopter navigation beacons may generate high power, and therefore cause
ignition should any gas be present close to the transmitter aerial (antenna). In any