Understanding Common HazLoc Terminology

Overview
Explosion proof. Intrinsically safe. Non-arcing. Hazardous approved. When creating an electronic system within a hazardous location, these terms often get used interchangeably. However, the specific term used to describe the setup can make a big difference and, in turn, impact the entire system's integrity. This blog post explores some of the more common terms on a broad level and the situations in which they are used.

Hazardous Location
Also commonly referred to as "HazLoc," this is simply a general term for any location that is potentially hazardous. In particular, it is an area where a fire or explosion could occur as a result of flammable gases, vapors, liquids, dust, fibers/flyings in sufficient quantities to cause ignition. This term does not, however, indicate how large the risk of ignition is or what the best method of prevention is. Those items are broken down into Classes, Zones, and Protection Methods, respectively.

A firefighter attempts to extinguish a fire inside of a factory.

Protection Methods
To adequately explain what protection methods are in hazardous locations, it is beneficial to provide some background into what factors can cause fires and explosions. In order to achieve ignition, you need to have three items:

An ignition source
Fuel
An oxidizing agent (usually oxygen)

Removal of any one of these will either extinguish or prevent a fire.

There are different risk levels for every environment in regard to these three combustible elements. For example, a spark from static that you have generated by walking over a carpet is less likely to be a sufficient source of heat to cause ignition than a propane torch. However, that static electricity could become sufficient when you are in a room filled with hydrogen.

Man in protective gear welding a metal cage inside of a factory

Therefore, it is important to assess the location where the electronic system is being installed in order to determine where the largest risk factor is and how restrictive the components need to be. This is why there are different methods of protection. In one environment, you may have electronic items that are an ignition source and the best path is to contain that potential explosion so as to not cause harm to any person or piece of equipment. In another environment, it may be most practical to purge all the oxygen so the system can run as normal without fear of combustion. In many cases, the only course of action is to eliminate all sources of ignition altogether so you can work safely with the flammable material. These are all defined in different protection methods.

Intrinsically Safe
Intrinsically safe is one of the most stringent protection methods and is aimed at eliminating any arcs and sparks with enough energy to ignite a vapor. As the name suggests, these products are safe by design and can be located directly in the hazardous zone without the need for an additional enclosure. As this protection method is used for the most volatile environments, a barrier is required.

A rendering of an empty CTC IS200-20A intrinsically safe barrier enclosure with clear front panel.
IS200 Barrier Enclosure, compatible with IS111 Accelerometer Barriers, NEMA 4X, holds 1 to 20 barriers

A render of a CTC IS111 intrinsically safe barrier standing vertically.
IS111-1B Intrinsically Safe Barrier, for use with Class 1, Division 1/Zone 0,1 Sensors

A barrier is a device that is placed outside of the hazardous zone, or in a less hazardous zone, and controls the amount of voltage, current, inductance, and power that the electronic device receives. The properties that the barrier controls along with capacitance are known as entity parameters. When taking into account these properties, the entire system from the barrier to the electronic device is to be controlled, including the capacitance of the cable running through the device. For example, a device powered by 100 ft. of cable will have higher capacitance than a device with 10 ft. of cable. These parameters will be explained in further detail in subsequent sections.

In the United States, there are different divisions that state the level of hazard present. Intrinsically safe protection methods are necessary in Division 1 applications. Most of the world uses Zones instead. In this case, intrinsic safety is used in Zone 0 and 1. The topics of what Divisions and Zones are will be discussed in subsequent sections.

Molten steel on industrial conveyor inside a steel mill

Non-Arcing / Increased Safety
Sometimes the area in which an electronic device is located is only subjected to a hazardous environment intermittently or if an accident occurs causing a normally safe environment to become hazardous. When this is the case, a less strict approach to protection can be used. The protection methods of non-arcing and increased safety are similar in that the design of the electrical device(s) is examined to make sure it cannot produce a large enough ignition source to cause combustion.

Because the risk is not as great, the threshold of what is considered large enough is increased, and you do not need to use a barrier in this case. However, some additional measures must be taken. Cable requirements in America (defined in NFPA 70, formerly the National Electrical Code) are used in place of a barrier. Where intrinsically safe has been used in Division 1 (North America) and Zone 0,1 (international), the non-arcing protection method has been used to control Division 2 and Zone 2 respectively. In recent years, however, the increased safety protection method has begun to replace non-arcing in these locations. Different standards are used to evaluate the electrical devices prior to certification, but the locations and principles are the same.

two black cables with exposed wires and electrical spark

Explosion-Proof
Sometimes there is simply no way to design a product that works for either of the protection methods above. For example, there may be a circuit that would not function without capacitances that exceed the allowable values and could cause a spark large enough to cause ignition. One way to still use these products in hazardous environments is to enclose the entire device. This is the explosion-proof protection method. Explosion-proof does not mean there is no explosion. Rather, any explosion that does occur cannot escape the enclosure the device is within. This allows those installing the devices to have more flexibility on what they are installing. However, the enclosures are bulkier, difficult to install, and can be more expensive.

Classes
In North America, the type of hazard is broken down into classes:

Class 1 - Gases
Class 2 - Dust
Class 3 - Fibers/Flyings

Dust and fibers are interesting cases because they can come from shavings of materials that would not normally be hazardous when in a solid form.

Man using industrial concrete saw in cloud of dust.

Divisions
As mentioned in the protection methods section, the North American protection scheme is broken down into divisions. Divisions represent how frequently the electronic device is within the hazardous location.
Division 1 means that the electronic device is continuously exposed to the explosive material. If there was a pressure gauge within the storage tank of a gas station, it would be Division 1. Division 2 is the area surrounding Division 1. Devices in this location are only exposed to the combustible material in the event of an accident or fault condition. The outside area directly outside the storage tank would be Division 2. In normal operating conditions, the outside of the tank would have no hazards unless the tank ruptured.

Zones
Zones are the international version of Divisions. The major difference is that Zones are broken into three locations instead of two. Zone 0 is the direct equivalent of Division 1, meaning that the dangerous environment is always present. Zone 1 does not have an equivalent in North America, and it represents an environment that is exposed to hazards intermittently. For example, at a gas station, the inside of a storage tank would be considered Zone 0. The pump itself releases explosive gasoline every time someone tries to fill up their car. The pump handle would be considered Zone 1. Zone 2 is the same as Division 2 and the area outside of the storage tank or sufficiently distant from the pump handle would fall into this category.

Work crew watching excavator bury a large industrial fuel tank in the ground.

Note: For both Zones and Divisions, there is no set distance from the hazardous location where Zone 0,1 or Division 1 ends and Zone 2 or Division 2 begins. It is up to those making the risk assessment to establish this in accordance with the local jurisdiction. The type of material, its state (solid, liquid, gas), any barriers between the locations, and other risk factors are to be considered and it may be different in each case.

Groups
Within each Class, Division, and Zone, the location can be broken down again into the type of material. North America gives them alphabetical characters, with A being the most hazardous and G being the least hazardous. Internationally, special characters are used as seen in the chart below. if a product is rated for group A or IIC, it automatically qualifies for any of the less explosive groups. This is the same with B/IIB, all the way down.

Entity Parameters
Electronic devices that have been rated for use in hazardous locations generally come with a set of entity parameters. These are a set of electrical specifications that are to be maintained in order to achieve a safe design. These specifications say how much voltage, current, power, capacitance, and inductance can be applied to the device. Anything above the parameters would not be in compliance with the intended use and can cause an accident to occur. In the most hazardous locations, barriers are necessary to control these parameters. As stated in the intrinsically safe section, the entire circuit including the cable to the device is to be taken into consideration when ensuring the entity parameters are met.

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