Intrinsically Safe

In a world of ever-increasing industrial complexities, control of potentially explosive atmospheres has become vital, not least in terms of Fire Detection. There is little purpose in having a Fire Warning & Evacuation System if that very equipment itself causes an explosion to take place.

Since its inception in the early 1900's (as a result of mining disasters), Intrinsically Safe Devices have evolved dramatically and now provide protection of life and property in hazardous locations in virtually every industry sector worldwide.

Examples of Industries and Processes that require explosion protection are:

The danger which exists is that of ignition of flammable atmospheres leading to fire or explosion - a small spark from a piece of equipment in a grain silo, paint spray booth or petrochemical plant can all lead to an explosion and a disaster.

However in order for an explosion to take place three conditions must be present:

1. Combustible material (gas, vapours, dust etc.)
2. Oxygen
3. Electrical or thermal energy (of sufficient value)

If one of these conditions is not present an explosion cannot occur.

In order to prevent an explosion occurring therefore a means must be employed to eliminate one or more of the above conditions.

This is commonly achieved by either:

1. Explosion proofing
2. Pressurization
3. Installation of intrinsically safe devices

(Other less common methods are powder filling and 'increased safety')

Intrinsically safe equipment is defined as "equipment and wiring which is incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmosphere mixture in its most easily ignited concentration".

In simple terms this means that intrinsically safe equipment and wiring limits electrical and thermal energy to a level below that required to cause an explosion.

Intrinsic-safety equipment operates on lower power levels so there is no shock hazard due to excess thermal energy and arcing. Safety barriers are grounded to be effective under fault conditions; intrinsic safety is provided through voltage and current limiters. Zener diodes and resistors that provide this limiting are usually mounted away from hazardous areas. Failure to replace enclosure covers or bolts will not imperil protection.

Intrinsically safe systems tend to be small and do not require expensive, bulky accessories such as explosion-proof enclosures, seals and rigid metallic conduits, a design that generally makes easy handling and installation. Explosion-proof enclosures and conduit are no longer necessary, so labour and material costs are lower.

Equipment can be calibrated and maintained without disconnecting power, which means easier maintenance and decreased down time. Field instruments may be maintained and calibrated with power applied, thereby minimizing downtime.

Since properly installed intrinsic-safety circuits and equipment reduce the probability of explosion to practically zero, insurance rates tend to be lower; especially where local ordinance requires hazardous facilities to carry special liability insurance.

The principle of an intrinsically safe fire detection system are virtually identical to those of regular detection systems and may include smoke detection devices as well as special-purpose detectors such as flame detectors, heat detectors, air sampling etc.

Intrinsically safe wiring must be separated from non-intrinsically safe wiring by at least 2 inches in order to prevent the transfer of unsafe levels of energy to the hazardous area and it is vital therefore that planning and installation of such systems are undertaken with utmost care and attention.

Intrinsically safety can be compromised after initial installation due to improper maintenance or repair and it is important to ensure such works are always carried out by specialists.

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