There is no such thing as explosion PROOF.

Nothing is absolute, and only an acceptable level of hazard can be obtained.

Explosions must be mitigated through design, build, operation and maintenance phases.  A useful tool for this is education, hence the article.

Staff Education

Part of mitigating Explosive situations is educating everyone involved about the potential for an explosion. Staff need to be trained on when and how an explosion can happen and how to avoid it.  Not only staff, but product manufacturers,  designers, operators, maintenance, janitors, electricians, hvac, general contractors all need to be enrolled in safety.

Explosions can be mitigated by removing one of the three elements in the ignition triangle.

3 Requirements for an Explosion

Ignition sources:

• Hot Surfaces
• Electrical Sparks
• Friction and Impact Sparks

Flammable Substance 3 Categories:

• Gas
• Liquid/Vapor
• Solid

Oxidizer

• Air

North American Area Classification

• Class I locations are those in which flammable vapors and gases may be present.
• Class II locations are those in which combustible dust may be found.
• Class III locations are those which are hazardous because of the presence of easily
  ignitable fibers or flyings.

Europe has a different classification, which is ATEX.

Temperature Class

This is the maximum operating surface temp so as not to ignite the designated substance.  The ratings start at temperature class T1

Protective Methods for Hazardous Areas

Explosion Proof Enclosures

Article 100 of the NEC provides the following definition for Explosion-Proof Apparatus:

Apparatus is enclosed in a case that is capable of withstanding an explosion of a specified
gas or vapor that may occur within it and of preventing the ignition of a specified gas or
vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within,
and which operates at such an external temperature that a surrounding flammable
atmosphere will not be ignited thereby

*Type 7 enclosures are designs to meet explosion-proof requirements.

Here is an example of a non-NEMA, XP Box which contained an explosion from ethanol getting inside of the box and exploding.

Dust Proof Enclosures

Conduit and Cable Seals

The NEC requires sealing each conduit run entering an enclosure that contains apparatus
which may produce arcs, sparks, or high temperatures. These seals are to be installed
within 18 inches of the enclosure. This prevents the propagation of flames and explosive
pressures from the interior of an enclosure into the conduit system.

Ways to Limit the Energy

Intrinsic Safety – Intrinsically safe equipment and wiring shall not be capable of
releasing sufficient electrical or thermal energy under normal or abnormal conditions to
cause ignition of a specific hazardous atmospheric mixture in its most easily ignited
concentration.

Pneumatics – Air powered valves and motors

Fiber Optics – inherently safe as they are powered by light. No way to make elevated temps or spark.

Ways to Isolate the Hazard

1. Pressurizing and Purging
2. Oil Immersion
3. Hermetic Sealing
4. Encapsulating(Potting)
5. Restrictive Breathing

Here’s a chart to help read XP Tags.

To learn more, visit https://literature.rockwellautomation.com/idc/groups/literature/documents/wp/800-wp003_-en-p.pdf

Love and Blessings.