What are the standards for explosion-proof enclosures?

Industrial facilities and manufacturing plants have hazardous locations in which hazardous and explosive gases could be present. Explosion-proof enclosures are used by such facilities to ensure the safe housing of electrical components that could cause a spark and ignite these gases in the atmosphere.

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What Is An Explosion Proof Box or Enclosure?

They are a cast aluminum or iron box that can withstand a heavy-duty explosion from gas entering the box and igniting, and then containing the explosion. These boxes are designed in such a way that they can significantly reduce the risk of the flame getting outside of the box and igniting the atmosphere where flammable vapor, gases and dust particles are present. Places like oil refineries, feed mills, chemical plants, plastic plants and fireworks factories are a few such industrial facilities that employ explosion-proof enclosures. Their primary purpose is to protect industrial equipment and devices against internal explosions.

Why Should You Use Explosion Proof Enclosures vs. Non-Explosion Proof?

If your industrial facility is located in an area that has been designated as hazardous according to the standards of the National Fire Protection Association (NFPA) and if your facility is utilizing electrical components like circuit breakers and switches, you need to use certified explosion-proof enclosures. Why is doing so important? Remember that the success and productivity of any industrial facility depends on how much importance it gives to safety. Hence, by using explosion-proof enclosures, your plant will comply with the regulations of the Occupational Safety and Health Agency (OSHA), the location classifications outlined by the National Electric Code (NEC) and the specifications crafted by the National Electrical Manufacturers Association (NEMA). Using Non-Explosion Proof standard electrical enclosures in a hazardous area is comparable to a hand grenade. Flammable gases can fill up in the enclosure and when a spark occurs from one of the devices inside it will cause an explosion throwing shrapnel metal, electrical components and igniting the atmosphere causing a chain reaction explosion in the facility.

A major advantage of using explosion-proof enclosures, or &#;IS&#; cabinets by Spike Electric, is that they prevent an internal explosion or inferno from spreading to the surrounding area. Ultimately, these explosion-proof enclosures ensure the safety of the facility and more importantly the personnel working in it. Using these safe and effective enclosures will help in preventing property damage and will ensure that you, your manufacturers and investors don&#;t have to endure heavy financial damage in the event of an explosion.

The Mechanical Design Features of Explosion Proof Enclosures

What does it take to make an effective explosion-proof junction box or cabinet? An incredible mechanical engineering design is what you need. Design for such enclosures and storage boxes differ with each manufacturer. Since the requirements of every industrial facility and the intensity of hazardous locations vary, different strategies are adopted to develop the design for these enclosures and storage boxes. Below are some common techniques that are used for explosion-proofing that we have curated for you.

Typical Ratings on Cast Aluminum or Cast-Iron Explosion Proof Enclosures

NEC, CEC and CSA: &#; Class I, Division 1 & 2, Groups B, C, D &#; Class II, Division 1 & 2, Groups E, F, G &#; Class III &#; UL Standard &#; cUL to CSA C22.2 No. 30, No. 25 &#; NEMA Type 3, 3R, 4, 7BCD, 9EFG &#; Enclosure Type 4X

European IECEx: &#; Ex db IIB+H2 Gb &#; Ex tb III C Db IP66 &#; -20°C &#; Ta &#; +60°C &#; IECEx ETL 13.U

European ATEX: &#; II 2 G D Ex db IIB+H2 Gb &#; Ex tb IIIC Db IP66 &#; -20°C &#; Ta &#; +60°C &#; ITS13ATEXU certified

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Flame Proofing

Who should be adopting flameproofing? Industrial facilities that operate in environments with high-pressure systems should adopt flame-proofing for the design of safety cabinets and enclosures. With the help of the flame-proofing technique, if there is an internal spark or an internal ignition within the framework of a device, the proofed enclosure will control the impact of the resulting explosion. In flame-proofing, strong and firm materials like cast metal and fabricated steel are employed to build the outer shell of the storage cabinet. With flame-proofing, you can ensure the control of any excess pressure resulting from an internal eruption. This will ultimately prevent the spread of the fire to the immediate surroundings of the enclosure.

Ingress Protection (IP)

Ingress protection is a process that involves the protection of electrical enclosures to prevent the entry of vapor, dust and other foreign particles in an electrical enclosure. In environments where water or dust could damage electronic components, a sealed enclosure is used to prevent such ingress and safe house the electrical equipment.

Pressurization Or Purging of Gasketed Standard Electrical Enclosure

Explosive gas or vapor mixture that accumulates within an Explosion Proof cabinet tends to give rise to dangerously high pressure. As a result, the electrical components will become heated beyond the safe limit and can potentially give rise to ignition or sparking. Purging involves a segregation method that supplies a protective non-explosive gas into the enclosure like nitrogen. Pressurizing also hinders the entry of dust that may be potentially combustible into the metallic box. Standard Non-Nema 7/9 cast enclosures would not be used in this application. A minimum of Nema 4 gasketed enclosure rating is suggested for a purged electrical cabinet. For larger cabinets this maybe the more cost-effective route rather than a large bolted Nema 7 enclosure.

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Encapsulation

What does encapsulation involve? The explosion-proof enclosure or cabinet is filled with a resin that provides significant resistance to particular environmental conditions. During the process of encapsulation, the resin isolates the electrical components that may potentially lead to sparking, heating, and the ignition of explosive gases, vapors or other dust and fine particles.

Explosion Proof and &#;IS&#; Enclosures- How Do They Vary?

The primary distinction between an Explosion Proof Enclosure and an Intrinsically Safe (IS) enclosure is that the former follows a strategy involving containment whereas the latter is about offering prevention. To state simply, IS enclosures eliminate the risk of ignition or explosion by following a prevention technique, unlike explosion-proof enclosures that offer protection after the problem has occurred.

The design of IS enclosures ensures the safety of the electrical framework of a component. The primary purpose of these enclosures is to minimize the values of current, voltage, and temperature of the circuit of a device while it is operating.

An intrinsically safe junction box or cabinet provides notable resistance to overheating. Hence, this enclosure is suitable for use in industrial facilities that function in high-temperature environments. The circuitry of an IS enclosure does not produce sparks or electric discharges which can trigger an explosive mixture of gas or vapor sense intrinsically safe components must be used.

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What Is An Explosion Proof Junction Box?

Junction boxes are an ideal choice for industrial plants that allow rigid conduit systems to be connected and operate in potentially explosive surroundings. For example; gasoline pumps. These boxes are designed to contain electrical components and wiring that may initiate a spark or an ignition. These types of enclosures are rain-tight, heavy-duty that are explosion-proof.

What Are Intrinsically Safe Barriers?

They control the amount of energy transported to electrical equipment in hazardous environments. IS barriers restrict the energy supply to circuits. This helps in the prevention of the ignition of combustible substances in various systems. For example, dangerous power surges may cause the ignition of explosive gases which might spread to the surrounding environment.

Available Ratings For Different Designs of Explosion Proof Enclosures

Every Explosion Proof Enclosure, intrinsically safe barrier, junction box or any other containment enclosure should comply with the standards outlined by NEC Hazardous Area Classifications. The design, framework and functionality of all these enclosures should abide by the defined regulations. However, manufacturers have the liberty to comply with significant ratings by NEMA. What are the NEC specifications that you need to abide by? That completely depends on whether you intend on deploying an Intrinsically Safe Cabinet or an Explosion Proof Enclosure. Given below are a few NEMA or NEC classifications and ratings for Explosion Proof and Intrinsically Safe Enclosures that we have curated for you:

• NEMA 1 The NEMA 1 standard is for those electrical enclosures that are intended to function indoors. The main purpose of storage boxes with a NEMA 1 rating is to ensure the prevention of housed electrical components coming into contact with falling dirt. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust and vapor mixtures.
• CSA or NEMA 2 Enclosures are intended to function indoors and used primarily to provide a degree of protection against limited amounts of falling water and dirt. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust and vapor mixtures.
• CSA or NEMA 3 Enclosures are intended to function outdoor use primarily to provide a degree of protection against rain, sleet, windblown dust; and damage from external ice formation. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust, and vapor mixtures.
• CSA or NEMA 3R Enclosures are intended for outdoor use primarily to provide a degree of protection against rain, sleet and damage from external ice formation. They must have a drain hole. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust and vapor mixtures.
• CSA or NEMA 3S Enclosures are intended for outdoor use primarily to provide a degree of protection against rain, sleet, windblown dust, and to provide for operation of external mechanisms when ice laden. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust and vapor mixtures.
• CSA or NEMA 4 Enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust, rain, splashing water, hose directed water and damage from external ice formation. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust and vapor mixtures unless a pressurized purge system is integrated into the enclosure.
• CSA or NEMA 4X Enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against corrosion, windblown dust, rain, splashing water, hose directed water and damage from external ice formation. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust and vapor mixtures unless a pressurized purge system is integrated into the enclosure. Type 4X box is recommended for a pressurized purge system for hazardous locations.
• CSA or NEMA 5 Enclosures are intended for indoor use primarily to provide a degree of protection against settling airborne dust, falling dirt and dripping non-corrosive liquids. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust and vapor mixtures.
• CSA or NEMA 6 Enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against hose-directed water, the entry of water during occasional temporary submersion at a limited depth; and damage from external ice formation. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust, and vapor mixtures.
• CSA or NEMA 6P Enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against hose-directed water, the entry of water during prolonged submersion at a limited depth and damage from external ice formation. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust and vapor mixtures.
• CSA or NEMA 12 Enclosures are intended for indoor use primarily to provide a degree of protection against circulating dust, falling dirt and dripping non-corrosive liquids. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust and vapor mixtures.
• CSA or NEMA 12K Enclosures with knockouts are intended for indoor use primarily to provide a degree of protection against circulating dust, falling dirt and dripping non-corrosive liquids. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust and vapor mixtures.
• CSA or NEMA 13 Enclosures are intended for indoor use primarily to provide a degree of protection against dust, spraying of water, oil and non-corrosive coolant. These enclosures are not intended for hazardous areas and will not protect against explosive elements like combustible gas, dust and vapor mixtures.
• NEMA 7 NEMA 7 enclosures are meant for operation in hazardous locations that have been designated as Class 1, Group A, B, C, or D hazardous environments by NEC. These enclosures are designed to contain high pressure resulting from an internal explosion of gases. Additionally, these enclosures also restrict the effect of any such explosive combustion from causing ignition in flammable gas-air mixtures in the immediate surroundings. They prevent the spike in the temperature of external surfaces that might cause an explosion in the immediate surroundings.
• NEMA 8 Enclosures have the same protection as Nema 7, but they are for indoor or outdoor use in locations classified as Class I, Groups A, B, C, or D, as defined in the NEC. Most of the time you will not see a Nema 8 rating on a hazardous location box. You will see a Nema 7/9 with a Nema 4, 4x or 3R outdoor rating.
• NEMA 9 NEC designated locations such as Class 2, Groups E or F employ NEMA 9 rated enclosures. What is their purpose? To state simply, they help prevent the entrance of dust. Any housed electrical component that generates heat should not cause a spike in the temperature of external surfaces up to the ignition point. Why? It may lead to the lighting of combustible mixtures in the surrounding environment. Hence, NEMA 9 rated enclosures are employed to regulate the temperature.
• NEMA 10 Enclosures are constructed to meet the applicable requirements of the Mine Safety and Health Administration. (MSHA)

What Is International Electro-Technical Code (IEC) Zoning?

The International Electro-Technical Code (IEC) Zoning segregates or categorizes hazardous areas depending on the properties of combustible substances that they contain. This zoning process also considers the possibility of the presence of combustible gases, vapors or dust in a particular environment.

Article 505 from NEC publication outlines the classifications of similar locations. For example, consider the A Zone 1 designation. This zone refers to d-rated flame-proof enclosures that are meant to function in environments that may potentially consist of combustible measures of flammable gases while operating normally. This article also mentions e-rated cabinets hosting electrical components that do not produce electrical discharges, sparks or extremely high temperatures while operating under normal conditions.

When Can You Use Purge Or Pressurizing Enclosures?

Article 500 of the NEC allows the usage of purged or pressurized cabinets as a substitute for Explosion Proof Enclosures. When? Only under specific circumstances. Primarily, these enclosures should satisfy the requirements outlined by the  NFPA 496 regulation. IEC Zone 1 and 2 also mention specifications concerning purged and pressurized storage systems.

Conclusion

Industrial facilities use Explosion Proof Enclosures, IS cabinet boxes or other types of pressurized purged enclosures to ensure the safety of electrical equipment and the personnel amidst various types of hazardous materials like combustible gases, vapors and dust. These industrial facilities are getting their hardware for hazardous area operations constantly updated according to intrinsically safe standards. Through this, they can successfully prevent explosions and fire accidents that might cause severe damage to personnel and equipment in the facility. Most significantly, OSHA can charge a heavy penalty on companies and industrial facilities that don&#;t employ IS or Explosion Proof Enclosures to strengthen the safety factor while carrying out operations in dangerous environments, notably in places of high temperature and high pressure.

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Are you in search of explosion-proof enclosures for your industrial facility? Do you want to purchase an ideal enclosure for use in a hazardous environment? Step into our Spike Electric&#;s certified shop for enclosures and industrial explosion proof products. With plenty of expert guidance through the purchase, you will not be disappointed!

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.  

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