In the production process of petrochemical, pharmaceutical, chemical, energy and other industries, flammable and explosive gases such as methane, ethanol, hydrogen, and acetone are involved. The mixture of these gases and air may cause explosions when encountering electric sparks and high temperatures. Electrical components, compressors, electric control boxes, electric heaters and other components in industrial chillers will generate arcs and heat during operation, which poses a safety hazard. Therefore, chillers used in these environments must have explosion-proof designs.
 
So what are the explosion-proof standards? How to interpret the nameplate of an explosion-proof chiller? This article explains the explosion-proof standards in North America to help you make the right decision when purchasing a cooling system.
 
Related：When do you need an explosion-proof chiller?

Explosion-proof standards

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In the United States and Canada, the explosion-proof certification system for industrial equipment is composed of a standard system (UL/CSA), an environmental classification system (Class/Division/Group), and a certification and listing mechanism (NRTL).
 
UL (Underwriters Laboratories) is the most authoritative safety certification standard organization in the United States, and many electrical explosion-proof product standards are formulated by it. CSA (Canadian Standards Association) is responsible for the certification of electrical products in Canada. CSA and UL basically recognize each other in terms of content, but they have different emphases on some technical details, such as CSA pays more attention to the operation safety in extremely cold areas.
 
Both are part of the NRTL (Nationally Recognized Testing Laboratory) system, which is recognized by OSHA (Occupational Safety and Health Administration). OSHA does not directly certify equipment. It only recognizes which certifications are valid. Only after passing the NRTL certification can it be considered compliant by OSHA, and enterprises can legally use these equipment in industrial applications, otherwise they may face fines, suspension of production and rectification, or even legal liability.
 
The Class/Division/Group system is derived from the NEC (National Electrical Code) American National Electrical Code, which is a reference for the selection of explosion-proof chillers.

Explosion-Proof standards – Classes

Class means the type of environment in which the equipment operates. Explosion-proof chillers are typically designed for Class I environments.

Class	Meaning	Example Environments
Class I	Presence of flammable gases or vapors	Petrochemical plants, natural gas facilities, paint spray booths
Class II	Presence of combustible dust	Flour mills, woodworking factories, coal dust areas
Class III	Presence of ignitable fibers or flyings	Textile mills, furniture factories

Explosion-Proof standards – Divisions

Division represents the degree of danger of the environment in which the equipment operates.

Division	Meaning	Presence Condition
Division 1	hazardous materials are present under normal or frequent conditions	Explosive gases may exist during normal operation
Division 2	hazardous materials are present only occasionally or under abnormal conditions	Explosive gases exist only in case of leaks or malfunctions

Explosion-Proof standards Groups

Class I gas environments are also divided into Groups A to D according to the type of explosive gas.

Group	Gas Type	Explosion Risk	Descrizione
A	Hydrogen	Very High	Very low ignition energy, high pressure
B	Ethylene Oxide, Acetylene	Very High	Highly reactive, extremely explosive
C	Ethylene	Medio	Common moderate hazard gas
D	Propane, Gasoline Vapor	Common	Most common hazardous environment, many factories fall under this group

For example, if a chiller is to be used in an ethylene environment, it means that even if it is operating normally, there is a dangerous explosive gas around it. Then the chiller must meet the structural requirements of Class I/Division 1/Group C.

Temperature Class

On explosion-proof chillers, you may see words such as T4 or T1 after Group. This represents the maximum allowable surface temperature of the equipment, which is used to ensure that the maximum surface temperature of the equipment is always lower than the auto-ignition point of the flammable gas. Among them, T1 is suitable for high auto-ignition point gases, and T6 is used for extremely flammable materials (such as CS₂).

Temperature Class	Maximum Surface Temperature (°C)	Example Combustible Materials
T1	≤ 450	Methane, Gasoline, Butane
T2	≤ 300	Ethylene, Cyclohexane
T2A	≤ 280
T2B	≤ 260
T2C	≤ 230
T2D	≤ 215
T3	≤ 200	Acetone, Benzene, Ethanol, Gasoline
T3A	≤ 180
T3B	≤ 165
T3C	≤ 160
T4	≤ 135	Acetaldehyde, Ethylene Oxide
T4A	≤ 120
T5	≤ 100	Diethyl Ether, Pentane
T6	≤ 85	Carbon Disulfide (CS₂)

How to read the nameplate of explosion-proof equipment?

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The nameplate of the equipment is like your ID card. Each field indicates the environment in which the equipment can operate safely. After understanding the Class/Division/Group system and Temperature Class, it is easy to understand the nameplate of the explosion-proof chiller.
 
Take Class I, Division 1, Group B, T3 as an example. This means that this equipment:
 
• Class I: There are flammable gases or vapors in the use environment.
• Division 1: Under normal working conditions, there may be explosive gas/vapor mixtures in the surrounding area.
• Group B: The flammable gases in the surrounding area have a high explosion hazard and low ignition energy.
• T3: The surface of the equipment will not exceed 200°C.

Common names on the nameplate

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In addition to the above information, there may be other markings on the nameplate.

Abbreviation	Meaning
Ex	A prova di esplosione
XP	Explosion-proof enclosure
IS	Intrinsically Safe
DIP	Dust Ignition-proof
GP	General Purpose
NEMA	National Electrical Manufacturers Association (used for enclosure ratings)
ENC	Enclosure