"Intrinsically safe" is a design technique where the equipment can not, under any possible circumstance, release enough energy to cause ignition of an explosive atmosphere. In other words, the equipment has been designed to be "intrinsically", or inherently, safe for use.

Intrinsically safe design is arguably the safest protection technique available. In recognition of this, intrinsically safe equipment was - until recently - the only equipment allowed inside the very high-risk Zone 0 areas.

Intrinsically safe design has the advantage of removing the cost, bulk, and weight of flameproof enclosures, because the techniques does not rely at all on the enclosure. It also removes the requirement for tethering a clean gas source, as with purge/pressurization. This allows the design of lightweight portable equipment, such as gas detectors, video cameras, mobile phones, handheld computers and inspection instruments.

Intrinsically safe electrical design is very technically demanding, and poses serious restrictions on what is allowed in the design. Generally, high-power equipment can not be made intrinsically safe, because such designs contain too much energy. Only low-energy designs are incapable of causing ignition of an explosive atmosphere.

Intrinsic safety was originally envisioned only for very simple circuits, such as simple process sensors and transducers, that needed to be inside the hazardous areas. As electrical design complexity has grown, intrinsic safety has been applied to more and more types of devices. It is now possible to certify very complex designs as intrinsically safe.

Intrinsically safe design is best pursued from the very first design stages. Attempting to convert an existing design to I.S. is often difficult, and - in a few cases - may be impractical or impossible. It is important to remember that not all designs can be made intrinsically safe.

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