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Hazardous Location Enclosures: The Definitive Guide for 2019

Explosions and fires occur frequently on industrial and manufacturing properties. They cause damage to equipment, harm employees and result in property damage and loss of profits.

According to the most recent findings by the National Fire Protection Association (NFPA) an average of 37,000 fires occur at industrial and manufacturing properties every year.

These incidences resulted in:


18 civilian deaths


279 civilian injuries


and $1 billion in direct
property damage

NFPA’s findings do not take into account the number of profits lost due to downtime.

Read the full report released in March 2018: Fires in Industrial and Manufacturing Properties.

To better protect your teams and investments, it is important to be aware of the risks associated with industrial processes. 

I. What are Hazardous Locations for Enclosures?
II. What Happens When an Enclosure Explodes?
III. Defining the Risks
IV. Markings/Certifications on Name Plate
V. How to Prevent Explosions Caused by Electrical Equipment
VI. Hazardous Location Additions for Enclosures

I. What are Hazardous Locations for Enclosures?

The Occupational Safety and Health Administration (OSHA) defines a hazardous location as:

Hazardous locations are areas where flammable liquids, gases or vapors or combustible dust exist in sufficient quantities to produce an explosion or fire. In hazardous locations, specially designed equipment and special installation techniques must be used to protect against the explosive and flammable potential of these substances.” Publication 3073

Easily ignitable gases or vapors, flammable liquids, combustible dust or ignitable fibers are present at almost any industrial building. They are used in, or as a result of production processes. They do not become a risk until there are significant amounts of hazardous substances present.

II. What Happens When an Enclosure Explodes?

Causes of Explosion in Enclosures

It sounds like a silly question, but let’s get technical for a second. An explosion is defined as a violent expansion in which energy is transmitted outwards as a shock wave. We have all seen big, dramatic explosions in our favorite action films, and while exciting on the big screen, explosions are disastrous in real life.

Explosions most frequently occur in chemical plants, refineries, paint shops, cleaning facilities, mills, flour silos, tanks, and loading facilities for flammable gases, liquids, and solids.

Factors That Cause Explosions:

All three sides of the triangle must be present for an explosion to occur, and it can all get started with a tiny little spark.

1. Flammable Substance (Fuel)

There must be enough flammable gas, liquid or vapors, or flammable solid to produce an ignitable or explosive mixture that could produce an explosion or fire. A fire must have fuel to burn, if a campfire doesn’t have any wood it will die out.

2. Oxidizer (Air)

An oxidizer is a type of chemical which a fuel requires to burn. There has to be enough of an oxidizer present to cause an explosion. Fires have to have air to burn. You can put out a candle by smothering the flame and cutting off its supply of air.

3. Source of Ignition (Heat)

A spark or high heat must be present. It’s impossible for a fire to start without a source to light it or heat high enough to cause the material to light on its own. Just like leaving a hot iron on a shirt for too long, it burns the fabric and can light the shirt and surrounding objects on fire.

Major Causes of Industrial Fires and Explosions:

What can start an enclosure explosion

In most cases, fires and explosions are preventable.

III. Defining the Risks

The National Fire Protection Association (NFPA) publishes the National Electric Code (NEC) 70, that defines hazardous locations through a system of classes, divisions and groups that enclosures and other equipment must be labeled for use in those areas. Hazardous area classifications are based on the type of substance or material that is present in the area, the likelihood that it exists, and more detailed specifics, such as ignition temperatures and combustible properties.

hazardous conditions for enclosures

Classes State the type of ignitable substances present that could potentially start fires or cause an explosion.

Divisions – Define the amount of time that a hazardous material is present during production processes.

hazardous areas for enclosures

Groups Specify materials, and are based on their ignition temperatures and explosive materials.

Temperature Class Definition Tell the minimum temperature at which substances will ignite because of high heat, or the temperature that substances will explode or begin to burn with no igniter like a spark or flame.

hazardous temperature for enclosures

Class I: Gases or Vapors

Class I locations are where flammable gases or vapors, are or may be present, in the air in large enough amounts that could cause an explosion. Common examples of flammable gases include hydrogen and methane. Vapor is released off of a liquid at normal atmospheric pressure, a common example of a vapor is gasoline. Not only will gasoline burn in liquid form, but the vapors it gives off are also flammable.

Typical Class I locations include airplane hangars, vehicle paint shops, commercial laundromats, and gas plants.

class I enclosures

Class II: Combustible Dusts

Combustible dust is a solid material composed of fine particles or pieces, regardless of their size, shape or chemical composition that becomes a fire hazard when suspended in air or another oxidizing medium. If dust is suspended in the air in the right concentration, under certain conditions it can become explosive. Some materials that are not flammable in large pieces in the right circumstances can become combustible as a dust, like aluminum or iron.

Typical locations include granaries, mines, sugar or starch plants, and plastic-producing factories.

Class II Enclosures

Class III: Ignitable Fibers

These materials are not in the air in quantities that are sufficient enough to cause an explosion, but they are a serious fire risk. Materials such as cotton lint, flax or rayon can form a layer throughout a facility and if it were to be ignited will cause a flash fire. Flash fires move quickly, at near explosive speeds.

Typical locations include textile mills, cotton mills, and sawmill facilities.

Class III Enclosures

Read Enough But Still Have Doubts?

IV. Markings/Certifications on Name Plate

Explosions can be prevented by using the correct equipment. Electrical Enclosures are rated and marked so that consumers can make educated decisions while selecting components.

The marking must indicate the following:

  • The manufacturer who has put the item on the market and who must be able to identify it.
  • The type or types of protection the enclosure conforms to.
  • The temperature class for which it is suitable.
  • The explosion hazard group or subgroup applicable.
  • The test center issuing the test certificate.
  • Any special conditions that have to be observed.
  • The standard or revision of the standard applicable.

Name Plate in Enclosures Markings and certifications

UL Certification:

Underwriters Laboratories (UL) is a global safety consulting and certification company and to be UL rated it means that a product has met specific nationally recognized standards for safety and is safe for use in certain environments.

V. How to Prevent Explosions Caused by Electrical Equipment

Remember the fire triangle? By limiting or inhibiting the three sides of the triangle, you can effectively prevent explosions and fires.

1. Confine the Explosion

The National Electrical Manufacturers Association (NEMA) defines standards used in North America for various grades of electrical enclosures usually used in industrial applications. Each is rated to protect against specific environmental conditions. A typical NEMA enclosure might be rated to provide protection against environmental hazards such as water, dust, oil or coolant or atmospheres containing corrosive agents like acetylene or gasoline.

By containing equipment, you remove the ignition side of the triangle. If hazardous materials do not come into contact with equipment that can start a fire by a spark or high heat an explosion or fire is less likely to happen.


  • Explosion Proof Enclosures
  • Dust Ignition-Proof Enclosures
  • Conduit and Cable Seals

2. Limit the Energy

Methods can be used to limit or eliminate the available energy, both electrical and thermal. Without energy, a piece of the fire triangle is missing and an explosion cannot occur.


  • Intrinsic Safety
  • Pneumatics
  • Fiber Optics

3. Isolate the Hazard

This technique prevents or delays the diffusion, or spreading, of a hazardous substance into an enclosure where a possible ignition could occur. Without a material to feed the fire, you eliminate a side of the triangle and prevent an explosion or fire from occurring.


  • Pressurization and Purging
  • Oil Immersion
  • Hermetic Sealing
  • Encapsulation (potting)
  • Restricted Breathing

VI. Hazardous Location Additions for Enclosures

HazLoc Enclosure Coolers

Hazardous Location (HazLoc) Duty Vortex A/C Coolers are designed specifically for purged electrical enclosures in Class I Div 2 Groups A, B, C, and D; Class II Div 2, Groups F and G; and Class III locations.

Hazardous Location Enclosure Coolers

When the unit’s integrated mechanical thermostat senses acceptable enclosure temperatures, the purge system creates positive pressure in the enclosure. This occurs as the HazLoc Vortex A/C’s integrated check valve seals off the cold air outlet, which allows the purge system to maintain the necessary pressure to block gases, vapors, dusts, fibers and contaminants from entering the enclosure.

The HazLoc Vortex A/C is specifically designed for simple installation and flexible mounting. Neither its mounting position nor cold air ducting is limited by the check valve’s design.

+ No maintenance required
+ Very easy and quick top or side mount installation, with no wiring, no electricity
+ Extremely reliable
+ Very quiet
+ Integral mechanical thermostat maintains 80° to 90° F temperatures
+ 10-year warranty
+ Operates in environments up to 175° F
– Requires a purge and pressurization system


Hazardous Location Air Conditioners

Designed to cool the internal environment of hazardous location enclosures that contain electrical equipment and are ideal for use on process control systems in chemical, petrochemical, refining, field and offshore drilling applications.

Hazardous Location Electrical Enclosure Air Conditioners

These Hazardous Duty enclosure air conditioners are rated for use with both purged and non-purged enclosures located in Class 1, Div II, Groups A, B, C & D hazardous environments.

+ Easy maintenance
+ Programmable digital controller with built-in alarms and remotes
+ For purged and non-purged enclosures
+ Equipped with a Condensate Evaporation System
+ Thermal Expansion Valve for maximum efficiency when temperature or heat load changes
– Investment costs


Purge and Pressurization Systems

Purging is the process of supplying an enclosure with compressed air (or inert gas) at the proper flow and pressure in order to reduce the hazardous gas inside the enclosure to a safe level. Pressurization is the process of increasing the air pressure within an enclosure to the point where there is no ingress of hazardous or combustible gases.

Enclosures Purge and Pressurization Systems

Type X

Type X Purging and Pressurization Systems reduce the classification within the protected enclosures from Division 1 to non-hazardous. These purge systems are fully automatic and perform critical purging, pressurization, and monitoring of an enclosure in a single dependable unit. This eliminates the guesswork of operation and increases the effectiveness system.

Type X systems operate by forcing air (or inert gas) through the enclosure for a specified time until all of the hazardous gas is removed. This creates a positive pressure which is maintained by either a continuous or compensating flow of air through the enclosure.

Type Y

Type Y purging and pressurization systems regulate and monitor pressure inside sealed enclosures, in order to prevent flammable vapor from contaminating the enclosure.

The Type Y system is designed to reduce the classification within a protected enclosure from Division 1 to Division 2. This allows Division 2 rated equipment to be operated in Division 1 locations.

Type Z

Type Z purging and pressurization system are rapid exchange purging systems that operate on a supply of compressed air or inert gas. It regulates and monitors pressure within one or more sealed enclosures, in order to rapidly remove and prevent flammable vapor accumulation within the enclosure.

It is rated for Class I, Division 1 to Division 2 area applications or Class II, Division 1 to Division 2 applications.

Still unsure of what hazardous location enclosure will fit your needs?

Needs vary so much from application to application it is hard to determine what will work best.

But you’re in luck! The staff at ISC Sales is very knowledgeable, able to answer any of your questions and will ensure that you get the most efficient product for your business. Contact us today and have the hazardous location equipment that’s perfect for you tomorrow.

Call ISC Sales today at 972.694.4291 to get a free quote or to ask about our lineup of industrial equipment. You can also request a quote online, HERE.

Hazardous Location Enclosures: The Definitive Guide for 2018
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Hazardous Location Enclosures: The Definitive Guide for 2018
To better protect your teams and investments, it is important to be aware of the risks associated with industrial processes. Hazardous Location Enclosures can help prevent explosions in many facilities! Find out More!
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ISC Sales
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