What Are Explosion-Proof Enclosures, and Why Should We ...

Author: Steve

May. 06, 2024

What Are Explosion-Proof Enclosures, and Why Should We ...

Explosion-proof enclosures are simple boxes containing electrical plugs, knobs, switches, and other components that can contain any explosion or spark within the box without exposing it to the outside environment. Industrial facilities that operate in hazardous environments require these enclosures because standard electrical enclosures are not designed to contain explosions. These robust, heavy-duty explosion-proof cabinets can reduce the risk of explosion in environments with flammable vapor, gases, and dust, such as oil refineries, chemical plants, fuel servicing sites, feed mills, and plastic/fireworks factories.

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Why Use Intrinsically Safe or Explosion-Proof Cabinets?

It’s important to find certified explosion-proof and intrinsically safe cabinets to store electrical components like knobs and switches if you’re using them in a space that the National Fire Protection Association (NFPA) has classified as hazardous.

Similarly, Explosion Proof and IS cabinets stop explosions or infernos from spreading from an internally exploding device to its surroundings. As a result, workers in industrial facilities that are prone to explosions will have a safer working environment.

What Is the Difference Between Explosion Protection and IS Enclosures?

The primary distinction between an Explosion Proof enclosure and an IS enclosure is that the former is a containment strategy, whereas the latter is a prevention strategy. In other words, intrinsic safety refers to preventing the possibility of ignition or explosion rather than merely containing an existing issue.

IS design places more emphasis on a component’s electrical architecture. The goal is to keep the device’s circuit current, voltage, and temperature as low as possible during operation.

An intrinsically safe junction box, for instance, is resistant to overheating and is suitable for use in industrial facilities that are subject to high operating temperatures. Its circuitry does not produce sparks or arcs that could ignite a gas or vapor explosive mixture.

Types of Explosion Proof Enclosures

Explosion-proof enclosures come in a variety of forms, including:

Junction boxes: These are perfect for rigid conduit systems in explosive environments, such as gas stations. They are equipped with heavy-duty, rain-tight explosion-proof enclosures to prevent internal explosions because they contain electrical components and wiring that could spark or short.

Cabinets: Explosion-proof cabinets store hazardous materials like flammable liquids and chemicals. They have a number of fire safety features, including strong steel enclosures for containing explosions and air vents for preserving safe interior temperatures.

Intrinsically safe barriers: These barriers regulate the energy supplied to electrical equipment in potentially hazardous environments. These systems stop combustible materials from igniting by limiting the energy supply to circuits. Isolated barriers, for instance, shield control circuits from dangerous power surges that could set off explosive mixtures in the vicinity.

Different Ratings That Are Relevant to Explosion-Proof Enclosure Design

Explosion-proof or intrinsically safe barriers, junction boxes, and other containment enclosures must be designed and built in accordance with the guidelines outlined in the NEC hazardous area classifications. Manufacturers, on the other hand, may voluntarily comply with relevant NEMA ratings. The following NEMA/NEC classifications and ratings apply to Explosion Proof / Intrinsically Safe enclosures:

NEMA 1

The standard applies to general-purpose enclosures used indoors. The primary goal of these storage boxes is to keep electrical components out of contact with potentially explosive gas, dust, or vapor mixtures.

NEMA 7

These enclosures are intended for use in locations designated by the NEC as Class 1, Group A, B, C, or D. They are designed to withstand pressure caused by an internal gas explosion. They also reduce the impact of any such explosive combustion so that it cannot ignite a flammable gas-air mixture in the immediate vicinity.

Related links:
A Quick Guide to Hazardous Location Lighting

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NEMA 9

Explosion-proof enclosures intended for use in NEC locations like Class 2, Groups E, or F must adhere to the type 9 standard. Their goal is to keep dust out of the enclosure. Any housed heat-generating component should not cause external surface temperatures to rise to the point where combustible mixtures in the surrounding environment ignite.

IEC Zoning: International Electro-Technical Code

The IEC classifies areas as hazardous based on the potential presence of flammable substances and their properties. It also accounts for the potential presence of combustible gases, vapors, or dust.

The Final Note: 

To reduce various types of risks, such as combustible gases, vapors, and dust in their operating environment, many industrial facilities store electrical equipment inside explosion-proof enclosures. In order to avoid explosions and fire accidents that could endanger personnel and cause property damage, these organizations are increasingly upgrading their hazardous area-certified hardware to intrinsically safe standards. 

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What is "Explosion Proof" and When is it Needed?

Explosion Proof (EP) is a crucial requirement for equipment intended for use in hazardous (classified) locations, as stipulated by the National Electrical Code, NFPA 70, Article 500. These locations are known to have potentially ignitable, flammable, or combustible atmospheres, where a mere spark could trigger an explosive reaction. To ensure safety, all electrical components installed in hazardous (classified) locations must be insulated from the atmosphere.

In electrically classified laboratories, electrical outlets and switches are enclosed in boxes that are intrinsically safe and rated as EP. Additionally, wiring in the lab is completely enclosed in conduit to prevent any sparks or potential ignition sources. Spark resistant construction is an absolute necessity for any equipment installed in these spaces. Components within a hazardous (classified) location must comply with EP requirements as defined by NFPA 70 to mitigate the risk of explosions and ensure the safety of personnel.

What is considered a hazardous (classified) location?

The National Electrical Code (NEC) and National Fire Protection Association (NFPA) 70 classify rooms with potentially explosive or flammable atmospheres as either Class I, II, or III and Division 1 or 2 within each of these classes. Class I locations refer to places where flammable gases or vapors may be present in the air in quantities sufficient to produce explosive or ignitable mixtures. Class II and III locations are rooms with the presence of combustible dust and fibers, respectively, and are not typical of the atmosphere in a laboratory environment.

If a fume hood is situated in an area with any of these electrical classifications, it should be rated as EP, irrespective of the nature of the activities performed inside it. This is because laboratories with a potentially flammable atmosphere must be devoid of any spark potential, including the electrical components situated outside the fume hood’s airstream.

What makes a fume hood classified as Explosion Proof?

It is a common misconception that working with a flammable chemical automatically requires an EP fume hood. However, only a small percentage of customers actually need EP fume hoods for their application. Many laboratories can effectively manage flammable chemicals with standard fume hoods that are properly ventilated and meet relevant safety standards.

When determining the need for an EP fume hood in your application, there are a few key factors to consider. Contrary to common misconception, EP hoods are not designed to contain explosions, but rather to minimize the potential for sparks that could ignite a flammable atmosphere.

In fact, most manufacturers define an EP hood as one that has been modified to eliminate spark potential outside the fume hood, reducing the risk of igniting a flammable atmosphere. These hoods are specifically designed to prevent sparks and potential ignition sources from escaping the hood and posing a risk in hazardous (classified) locations.

An EP laboratory hood is equipped with specially designed electrical components, such as EP rated switches, receptacles and internal wiring. The fume hood manufacturer does not supply these EP components, but instead, a licensed electrician installs them on-site in accordance with all state and local codes. For this reason, all EP modified Labconco fume hoods come with an EP rated incandescent light fixture and without bulbs, wiring, switches or duplexes.

Exhaust blowers serving hazardous (classified) locations

Spectrum™ Fiberglass Reinforced Polyester (FRP) and PVC exhaust blowers are designed to meet the requirements for applications in hazardous (classified) locations, when installed in accordance with ANSI/ASSP Z9.5 and NFPA 45 guidelines. As per NFPA 45, which is the standard for fire protection in laboratories using hazardous materials, exhaust fans used to remove hazardous substances must be located on the roof or exterior of a building. Adhering to these installation guidelines helps ensure the safe operation of exhaust fans and prevent any potential ignition sources from being present inside the hazardous (classified) location itself.

As stated in the American Society of Safety Professionals’ ANSI/ASSP Z9.5 standard, exhaust fans must conform to AMCA 99 for their construction. According to AMCA 99, exhaust fans that handle potentially explosive particles, fumes or vapors are required to have spark resistant construction for all components within the hazardous air stream, eliminating the risk of ignition.

Labconco’s Spectrum FRP and PVC exhaust blowers are designed with the highest level of spark resistant construction, adhering to Type A construction requirements as specified in AMCA 99. This ensures that these exhaust fans meet the safety standards for operation in hazardous (classified) locations, providing an added layer of protection against potential sparks and ignition sources.

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