Intrinsic Safety (IS)

 What Does Intrinsic Safety (IS) Mean?

Intrinsic safety is an explosion prevention technique used to ensure safe operation of electrical equipment in a hazardous area. It uses low-energy signaling technique by limiting the energy within the equipment well below the energy required to initiate an explosion. The equipment and control circuits can still operate with low currents and voltages that are adequate for its operation.

How does Intrinsic Safety Equipment work?

Avoiding ignition entails minimizing both the available power and the maximum temperatures. Defining the maximum level of available power is complex, but in general terms can be considered as meaning voltage less than 29V and under 300 mA. A simpler view is to say that power must be less than 1.3 W. (Note that much instrumentation requires 24V and can often be designed to draw less than 500 mA; sufficient to meet IS certification in many situations).

   

Six classes define temperature levels. In general, equipment meeting the T4 designation is considered intrinsically safe because temperatures will not exceed 135°C (275°F) (equipment dissipating less than 1.3 W generally stays below this temperature).

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:

Ø  4-20 mAdc Two Wire Transmitters

Ø  Thermocouples

Ø  Rtds

Ø  Strain Gages

Ø  Pressure, Flow, & Level Switches

Ø  I/P Converters

Ø  Solenoid Valves

Ø  Proximity Switches

Ø  Infrared Temperature Sensors

Ø  Potentiometers

Ø  LED Indicating Lights

Ø  Magnetic Pickup Flowmeters

What types of Intrinsic Safety equipment are available?

A wide range of industrial equipment, such as flashlights, cameras, gas detectors and even radios, are available in intrinsically safe forms. In terms of instrumentation the biggest need is for pressure and weight measurement. Temperature measurement generally meets the “simple apparatus” rule although temperature transmitters may be needed to send thermocouple signals over longer distances

               Pressure Transmitter                           Pancake style load cell

 

What are the benefits?

When electrical equipment and instrumentation must be placed in a hazardous environment, Intrinsic Safety barriers offer several benefits.

1.   It helps ensure a safe work environment and protects those nearby from explosion risks.

2.   It avoids the cost and bulk of explosion proof enclosures. Additional cost savings accrue from the ability to use standard instrumentation cables.

3.   Maintenance and diagnostic work can be performed without shutting down production and ventilating the work area.

4.   Insurance premiums may be lower as a result of the reduction in risk.

Installation and Risk Management Consideration

Installation is easier than setting up explosion proof enclosures. It is important to note that the whole system must be designed to be intrinsically safe. It is not sufficient just to purchase pressure sensors or load cells with Intrinsic Safety certification.

A system designed to be intrinsically safe requires full documentation of all the components and wiring employed. Immediately following installation there will be an inspection, followed by periodic inspections through the life of the equipment. This is to identify any deterioration or damage that may have occurred and any unapproved or unauthorized replacement of Intrinsic Safety system components.

Insulation and ground testing normally form part of an electrical inspection. However, such practices are not normally compatible with the IS concept. Specialist advice should be sought if these tests are needed.

 

Protection People and property

Many industrial, chemical and process environments have significant explosion risks, either due to the presence, actual or possible, of flammable gases and vapors, dusts or fibers. Such environments are termed “hazardous” and it is essential that they are designed so as to eliminate the possibility of igniting the flammable material.

Often it’s necessary to incorporate instrumentation of an electrical nature in such environments. When this is unavoidable there are three possible approaches: put the equipment in an explosion proof enclosure, purge the enclosure with inert gas, or adopt Intrinsic Safety design principles.

IS design minimizes power and heat creation. Equipment must be independently certified as Intrinsic Safety, and the whole system must be designed to IS standards before entering service. However, adopting IS design can simplify installation, save money, enable maintenance on live equipment, and most importantly, makes for a safer workplace.

Advantages:

The advantage of using the intrinsic safety technique is that it is the only technique that is allowed to be used under Zone 0 of the IEC (International Electrotechnical Commission) Classification system for the hazardous area.

By using intrinsic safety, there will be no possibility of an explosion in the system.

Disadvantages:

It can be used for only low power circuits, thus it cannot have heavy duty intrinsically safe motors. So intrinsic safety is mainly used for only measuring and controlling instruments like pressure transmitters, control valve positioners, small capacity valves, etc.

 

To prevent the ignition of vapors in a hazardous location, there are three different methods used by industries.

·         Containment (Explosion-Proof)

·         Segregation

·         Prevention

Containment is the only method where an explosion is actually permitted. The source of ignition is surrounded by an enclosure which is designed to contain the explosion to a defined area. This is what is meant by an “explosion-proof” enclosure. The safety of this method is entirely dependent on the mechanical integrity of said enclosure, so periodic inspections are necessary and should be mandated and scheduled. Some handheld test instrument manufacturers may use the term “explosion-proof” when they actually mean “intrinsically-safe.” Strictly by the definition of the former, this would imply that the instrument itself could explode internally instead of being designed not to ignite an explosion. THAT would not be a very worthwhile device to have on-hand at a facility – and certainly not one you’d want to be holding when it exploded!

Segregation is a method used to separate the ignition source from the hazardous material, using various isolation techniques. A few of these segregation techniques include using pressure differences to remove or separate the hazardous material from the ignition source, or by submerging the ignition source in an insulative oil, powder, or resin so that contact with the flammable material never occurs.

Prevention is the method where intrinsically safe practices and engineering are used to design devices that can be used in the hazardous environment so that these devices are virtually incapable of containing enough stored-up energy that could cause a spark that would ignite the hazardous material. This method is the preferred one due to the ignition source being omitted completely.