Intrinsic safety (IS) for sensors builders

Equipment that is used in a hazardous (potentially explosive) environment needs to be designed such that it is not going to cause ignition of flammable gasses, vapors, fibers or dust. Intrinsic safety is one of three main approaches to equipment design with regards to explosion protection, the others being explosion proofing and pressurization.

The word ‘intrinsic’ means ‘basic characteristic’, indicating that the equipment’s core design is focused on making it safe to use in an explosive environment. Intrinsic safety is generally focused on electrical/electronic equipment and lighting systems. Intrinsically safe equipment is designed so that it will not release electrical or thermal energies (sparks or heat) that could cause ignition in a hazardous area.

When is intrinsic safety equipment necessary?

Intrinsic safety equipment is necessary in hazardous areas (potentially explosive environments). In the European Union these areas are defined by the ATEX (Atmospheres Explosibles) Directive. This applies to any equipment, both electrical and non-electrical, that is used in a potentially explosive atmosphere. The following table summarizes the zones:

Flammable MaterialPresent ContinuouslyPresent IntermittentlyPresent Abnormally
Gas/vapor/mistZone 0Zone 1Zone 2
Combustible Dust/FibersZone 20Zone 21Zone 22

(More information about ATEX zones and certification can be found here.)

All electronics, lighting and other electrical devices have the potential to introduce thermal or electrical energy to a hazardous zone, either through malfunction or due to change in operating parameters. Making sure that the equipment used in these zones is designed according to intrinsic safety standards, greatly reduces the risk to people and property.

In order to be ATEX certified as intrinsically safe, the equipment or system has to be fully documented, pass the initial inspection as well as regular inspections throughout its working life. It is not sufficient for the individual components to be IS certified, the entire system has to pass the certification process.

What is intrinsically safe equipment?

Electrical and electronic equipment used in mines, chemical plants, oil refineries and other industries with explosive atmospheres needs to be intrinsically safe (IS) to ensure sparks and/or heat will not cause fires or explosions. There is a vast range of IS equipment such as lights, cameras, transmitters and valves. This equipment is sometimes referred to as non-incendive, however non-incendive equipment is only considered to meet ATEX requirements when it has been certified as intrinsically safe.

This is achieved by ensuring that equipment is designed to meet both of the following criteria:

  • current, voltage, and power is kept at a level so low that ignition (sparks and/or short-circuiting) is prevented. This is generally less than 1.3W
  • equipment temperature must be carefully controlled and are considered intrinsically safe if certified to meet the ATEX temperature level of T4. At this level, temperatures won’t exceed 135 °C

IS barriers are also added to the electrical circuits that are serving the IS equipment. They ensure that the amount of energy in the circuit is kept at a safe level. They also act like a safety valve for in the event of a power surge, ensuring the extra energy is prevented from entering the circuit.

In terms of temperature measurement equipment. Kamet’s temperature sensors generally meet the ‘simple apparatus’ rule. This rule exempts low power and passive devices, such as thermocouples and RTD’s from needing IS certification. However, the cables and transmitters carrying the signal do need to be IS certified.

Does intrinsically safe equipment replace explosion proofing or pressurization?

Intrinsic safety, explosion proofing and pressurization are different techniques for achieving the same outcome: prevention of fire and explosions in hazardous zones.

Intrinsically safe (IS) equipment prevents fires and explosions because they are designed such that they cannot release enough electrical or thermal energy to cause ignition.

Explosion proof equipment on the other hand, has an extremely robust enclosure and will contain and isolate fires or explosions, thus preventing the spread of combustion and damage

Pressurization or purging isolates (electrical) equipment from flammable atmospheres by purging its enclosure with inert gas. .

So IS equipment removes ignition sources by design, pressurization is an isolation or barrier method and in the event of accidental combustion, explosion proofing is able to contain fires and explosions.

The choice of explosion protection technique will depend on the particular process or project needs, the risk levels, installation options and budget. IS is usually the most cost-effective approach, both in terms of installation and maintenance. However it is not suited to systems that require high electrical currents, for example.

We have written an article on choosing temperature measurement components for potentially explosive atmospheres. For more information on this subject please click here.

For any further questions you may have about using Kamet components in an intrinsically safe set-up, please contact us and we’ll be happy to help.