Explosion Proof Enclosures: Safety Standards for Hazardous Area Operations

Explosion proof enclosures are indispensable to industrial facilities and other organizations that use or store electrical components in hazardous, explosion-prone environments. These sturdy, heavy-duty cabinets are built to minimize the risk of explosion in locations with flammable vapor, gases, and dust, such as oil refineries, chemical plants, fuel servicing sites, feed mills, and plastic/fireworks factories. Their primary purpose is containment in case a protected device explodes within itself.

Why Use Explosion Proof or Intrinsically Safe Cabinets?

If you’re using electrical components such as knobs and switches in an area that the National Fire Protection Association (NFPA) has designated as hazardous, you need to identify certified explosion proof and intrinsically safe cabinets to store these components. In so doing, you’ll be complying with Occupational Safety and Health Agency (OSHA) guidelines, National Electric Code (NEC) location classifications, as well as specifications set forth by the National Electrical Manufacturers Association (NEMA).

Likewise, Explosion Proof and IS cabinets prevent explosions or infernos from spreading to the surroundings of an internally exploding device. The net outcome is a safer work environment for personnel in industrial facilities that are prone to explosion. The safeguards also help to prevent damage to property, thus shielding investors or manufacturing facilities owners against potentially heavy financial losses.

Explosion Proof Enclosures’ Mechanical Design Aspects

Building an explosion proof junction box or cabinet is pretty much about mechanical engineering design. However, manufacturers may adopt different strategies to build these storage boxes for use in hazardous locations. Here are some common explosion-proofing techniques:

Flame Proofing

Industries that work with high-pressure systems should consider using flame-proof cabinets. With this containment technique, an enclosed device may spark internally or otherwise ignite an explosive mixture within itself, but its proofed enclosure shall limit the impact of any resulting explosion. Sturdy materials, such as cast metal or fabricated steel, are used to build the cabinet’s outer shell. Such a heavy-duty construction contains any excess pressure that an internal eruption creates, preventing propagation into the enclosure’s immediate environment.

Ingress Protection (IP)

Ingress protection involves sealing electrical enclosures to prevent the entrance of foreign bodies, such as vapor and dust.

Pressurization/Purging

Purging is meant to prevent high concentrations of any potentially explosive gas or vapor mixture from accumulating inside an Explosion Proof cabinet with electrical components capable of sparking or heating beyond acceptable temperature limits. This segregation method involves supplying a protective inert gas into the enclosure. Pressurizing, on the other hand, restricts the entrance of potentially combustible dust into the metallic box. 

Encapsulation

The encapsulation technique involves filling an explosion proof box with a resin that can resist specific ambient conditions. The material separates electrical components capable of sparking or heating to the point of igniting explosive gases, vapors, or fine particles.

What’s the Distinction Between Explosion Proof and IS Enclosures?

The main difference between an Explosion Proof and IS enclosure is that the former is a containment strategy while the latter is a prevention technique. In other words, intrinsically safe means eliminating the risk of ignition or explosion, rather than containing a problem that has already occurred.

IS design focuses more on the electrical architecture of a component. The objective is to minimize the current, voltage, and temperature of the device’s circuit during operation.

For example, an intrinsically safe junction box is resistant to overheating, and therefore, it’s appropriate for use in industrial facilities prone to high operating temperatures. Its circuitry does not generate sparks or arcs that can detonate an explosive mixture of gas or vapor.

Different Types of Explosion Proof Enclosures/Systems

There are different types of explosion proof enclosures or systems, including:

Junction boxes: These are ideal for rigid conduit systems in potentially-explosive environments like gasoline pumps. They have electrical components and wiring that may spark or short, so they come with rain-tight, heavy-duty Explosion Proof enclosures to internal explosions in check.

Cabinets: Explosion Proof cabinets are used to store hazardous substances, such as flammable liquids and chemicals. They have several fire-safety features, such as sturdy steel enclosures for containing explosions and air vents for maintaining safe interior temperature levels.  

Intrinsically safe barriers: These devices control the energy supplied to electrical equipment in hazardous areas. By restricting the supply of energy to circuits, these systems prevent the ignition of combustible substances. For example, isolated barriers protect control circuits from dangerous power surges that may ignite explosive mixtures in their immediate environment.   

Various Ratings Applicable to Explosion Proof Enclosure Design

The design and construction of an Explosion Proof or intrinsically safe barrier, junction box, or other containment enclosure must adhere to the standards defined in the NEC hazardous area classifications. However, manufacturers may voluntarily comply with relevant NEMA ratings. The right NEC specifications requirements for you depends on where you intend on deploying your Intrinsically safe or explosion proof cabinet. Here are selected NEMA/NEC classifications and ratings for Explosion Proof / Intrinsically safe enclosures:

NEMA 1

The standard applies to general purpose enclosures for indoor operation. The primary objective of these storage boxes is to prevent housed electrical components from coming into contact with potentially explosive gas, dust, or vapor mixtures.

NEMA 7

These enclosures are for use in locations the NEC designates as Class 1, Group A, B, C, or D. They’re built to contain pressure from an internal explosion of gases. They also limit the impact of any such explosive combustion such that it can’t ignite a flammable gas-air mixture in the immediate surroundings. As such, any enclosed electrical component must not heat external surfaces to temperatures capable of causing a fire or an explosion in the surrounding atmosphere.

NEMA 9

The type 9 standard applies to Explosion Proof enclosures meant for use in NEC locations such as Class 2, Groups E or F. Their objective is to prevent the entrance of dust. Any housed heat-generating component should not cause external surface temperatures to rise to the point of igniting combustible mixtures in the surrounding environment.

International Electro-Technical Code (IEC) Zoning

The IEC designates hazardous areas based on the properties of flammable substances that may be present. It also takes into account the possibility that combustive gases, vapors, or dust may be present. Article 505 of the NEC publication provides similar location classifications. A Zone 1 designation, for example, applies to d-rated flame-proof enclosures for use in environments that are likely to contain combustible amounts of flammable gases during normal operation. It also specifies e-rated cabinets housing electrical components that do not generate arcs, sparks, or extremely high temperatures under normal operating conditions.

Purge/Pressurizing Enclosures

Article 500 of the NEC permits the use of purge or pressurized cabinets as alternative Explosion Proof enclosures under specific conditions. For starters, these storage boxes must satisfactorily address NFPA 496 requirements. IEC Zone 1 and 2 also provide specifications for purged and pressurized storage systems.

Conclusion

Many industrial facilities are storing electrical equipment inside explosion proof enclosures to mitigate different types of hazards, including combustible gases, vapors, and dust, in their operating environment. These organizations are increasingly upgrading their hazardous area certified hardware to intrinsically safe standards to prevent explosions and fire accidents that could harm personnel and damage property. Most importantly, OSHA can heavily penalize companies that don’t use IS/Explosion Proof enclosures appropriate for their dangerous work environment, especially if operating in high-temperature and high-pressure conditions.  

Are you looking to buy explosion proof enclosures for hazardous area use? Head on over to our Intrinsically Safe Store for a high-quality product!