Hazardous Area Direct

Intrinsic safety (IS) is one of several techniques for preventing explosions in hazardous areas and is the most effective. Intrinsic safety operates by limiting the electrical energy in circuits and equipment to levels that are too low to ignite the most easily ignitable mixture of gas or dust that is ever likely to be present.
 

All other methods of protection such as oil filling or explosion proof enclosures rely on the continual maintenance of a physical barrier between the explosive atmosphere and the electrical circuit. Unfortunately any breach of the barrier renders the protection inoperative.

By contrast IS gives inherent protection by restricting the energy at its source and therefore has both commercial and technical advantages.

Circuits and equipment are designed so that safety is maintained both in normal use and under all possible fault conditions. Approvals can be given for individual components (entity approval) and complete systems.
 

Three elements are needed for a fire/explosion: fuel, oxygen and a source of ignition. An I.S. system assumes the fuel and oxygen is present in the atmosphere. Because of this assumption, which may or may not be true, the system is designed so the electrical energy or thermal energy of a particular instrument loop can never become high enough to cause ignition.

Traditionally, protection from fire/explosion in hazardous environments has been achieved by using explosion proof enclosures, or purging which isolates the explosive gas from the electrical equipment. Intrinsically safe equipment cannot replace these methods in all applications, but where possible can provide significant cost savings.

APPLICATIONS
A hazardous area may contain flammable gasses or vapors, combustible dusts, or ignitable fibers. There are different systems used in Europe or the United States to classify the type of hazard and whether the hazard is always present or only present in an emergency condition such as a spill or failure of venting equipment. In most cases the equipment is designed for the worst case, which would be to assume the explosive atmosphere is always present and the electrical or thermal energy is the lowest required to cause a fire or explosion.

Most applications require a signal to be sent out of or into the hazardous area. The equipment mounted in the hazardous area must first be approved for use in an intrinsically safe system. The barriers designed to protect the system must be mounted outside of the hazardous area in an area designated as Non-hazardous or Safe in which the hazard is not and will not be present.

Equipment which has been designed for and is available for use in hazardous areas with intrinsically safe barriers includes:

• 4-20 mA Two Wire Transmitters
• Thermocouples
• RTD's
• Strain Gages
• Pressure, Flow, & Level Switches
• I/P Converters
• Solenoid Valves
• Proximity Switches
• Infrared Temperature Sensors
• Potentiometers
• LED Indicating Lights
• Magnetic Pickup Flowmeters

Most of the apparatus that is mounted in the Hazardous area will have to be approved and certified for use in the Hazardous area with an approved barrier designed for use with that apparatus. Some simple devices like thermocouples, RTDs, LEDs and contacts can be used in the hazardous area without certification as long as it is wired in conjunction with an approved barrier.

APPROVALS
Intrinsic safety equipment must have been tested and approved by an independent agency to assure its safety. The customer should specify the type of approval required for their particular application. The most common Agencies involved are as follows:

Approval by any of the above European Agencies constitutes a CENELEC approval allowing the units to be considered approved in many of the European countries.