Electrical Heating In Hazardous Areas

Published 25 Sep 2016

  • Electrical Heating In Hazardous AreasBy Chris Dodds : estimated reading time 9 minutes

Directives such as ATEX and IECEx provide internationally recognised standards for the installation and use of electrical equipment in potentially explosive hazardous areas.

This article specifically focuses on Electrical Heating Equipment and has been written for all people who have an interest in understanding best working practices for installing and maintaining electrical heaters in potentially explosive atmospheres.

The European Directive 94/9/EC is in place to ensure manufacturers of process and hazardous area heaters, such as EXHEAT, meet stringent guidelines and only when these guidelines are satisfied can a product be certified for use in explosive atmospheres.

However, it is just as important that the end user knows and understands their responsibility for the safe installation, use and maintenance of such equipment.

Hazardous Area Heaters - Fan Assisted Portable

Electrical Heating In Hazardous Areas

EXHEAT Heaters Typical Hazardous Area Heating Applications.

In the UK, DSEAR (Dangerous Substances and Explosive Atmospheres Regulations) are provided by the HSE for employers with the aim “to protect people from fire and explosion risks related to dangerous substances and potentially explosive atmospheres. DSEAR places duties on employers to protect people from risks to their safety from fires, explosions and similar events in the workplace.”

Glasgow ICL Plastics Plant Explosion

Daily Record reports on Glasgow ICL Plastics Plant Explosion in 2004 that killed 9 people. The disaster brought into question if sub-contractors should be held responsible but ultimately it is the plant operators who should ensure safe working practices.

Offshore Platform

From the resultant investigation two main issues were raised. First, although the heater was certified for use in hazardous area, it was not suitable for the corrosive atmosphere it was being used in. Secondly, the duty holder did not have a comprehensive list of all such heaters in use and could not therefore carry out a routine planned inspection and maintenance program.



Pictured below are some common types of EXHEAT electrical heaters used for space heating and process heating in hazardous area locations and explosive atmospheres.

All such heaters should be installed, used and maintained strictly in accordance with manufacturers recommendations and under any conditions stipulated under its Ex certification.

Hazardous Area Heating

Electrical Heating In Hazardous Areas With EXHEAT


EXHEAT FAW Air Warmers – commonly used for space heating in paint stores or small plant areas storing flammable materials.


EXHEAT FLR Radiators – a flameproof radiator used for space heating in explosive areas such as laboratories, firework factories and ammunition stores.


EXHEAT Immersion Heaters – used for frost protection or pre-heating of oils, water and process liquids.


EXHEAT Flameproof Water Storage Heaters – for use in hazardous area locations such as washroom facilities on oil jetties.


EXHEAT HEF Enclosure Heaters – anti-condensation and space heater for small enclosures such as control & instrumentation cabinets.


EXHEAT In Line Heaters –  for frost protection and pre-heating applications including fuel oil heating to ensure pumping viscosity.

In order to appreciate the risks of electrical heating in hazardous areas, let’s first take a brief look at some of the fundamentals for understanding hazardous areas. If you’re an expert in this area you may wish to skip the next couple of paragraphs.

What Is A Hazardous Area?

Fire Triangle

Fire Triangle

To be specific a hazardous area is defined as “an area in which the atmosphere contains, or may contain in sufficient quantities, flammable or explosive gases, dusts or vapours.”

In such an atmosphere a fire or explosion is possible when three basic conditions are met.

This is often referred to as the “hazardous area” or “combustion” triangle.

Hazardous areas are assessed and defined by:

  • The types of hazard (gas, vapour, dust or fibre)
  • The likelihood that the hazard will be present in flammable concentrations (zoning)
  • Temperature Classification (Auto Ignition temperature)

There are many articles which go into great depth about hazardous areas, gas groups and zoning but I’ll skip past most of that and concentrate on Temperature Classification as this is particularly relevant to electrical heating equipment.

Temperature Classification (Auto Ignition Temperature)

To create an explosion you need fuel, oxygen and an ignition source. The ignition source is often thought of as a spark or flame. Obviously when using electrical equipment there is the risk of incendive arcs or sparks.

What also needs to be considered is the surface temperature of the equipment being used. All electrical equipment will give off some heat but the whole purpose of electrical heating equipment is to heat up and get HOT.

Hazardous Area Temperature (T) Classes

Hazardous Area Temperature (T) Classes

The T rating of an area refers to the temperature at which the flammable substance will auto ignite. See table above. For example, Acetylene has an auto ignition temperature of 300ºC and therefore the T classification for an area where Acetylene may pose a flammable risk would be T3 (Not T2, I’ll explain why in a moment).

This means electrical heating in hazardous areas should not be installed in that area unless it has a T classification of T3 or less.

T4, T5 & T6 would all be acceptable but T2 and T1 would not.

For example If you were to install a 30KW fan heater in such an area and the fan heater was rated T2, there is the potential for the fan heater surface temperature to reach 300ºC. Combine that with a flammable mixture of Acetylene and…. BANG.

Video – Acetylene Tanks Explode In Dallas Texas


Could a T4 rated air heater be used in an area where Ethyle Nitrate is a flammable risk (the auto ignition temperature of Ethyle Nitrate is 90ºC)?

If you know the answer, you understand T-ratings, if you don’t, give T&D a call and we can assist.

Just because an electrical heater is rated T3, the user also needs to consider ambient temperature conditions. As with all hazardous area certified equipment, heaters are certified under certain conditions.

For example, an EXHEAT FWDT-T3 is rated at T3 but the equipment is only permitted for use in ambient conditions of 60ºC<Tamb<+40ºC (see certificate example).  If the electrical heater is used in ambient conditions above the limit, there is a risk that the surface temperature will exceed 200ºC (T3).

Another risk is that any safety components (for example over temperature cut-out) may fail to operate if exposed to temperatures above or below the safe working range.


EXHEAT FWDT-T3 ATEX Certificate – Sample

Flameproof Air Warmers

EXHEAT FWD-T Flameproof Air Warmers – certified hazardous areas where the potentially explosive atmosphere is classified as a Zone 1 or 2 (IIA, IIB, IIC) gas group, or a Zone 21 or 22 (IIIA, IIIB, IIIC) dust group. If in about, call T&D.

Installation & Maintenance Of Ex Electric Heaters

Useful Information

Installation & Maintenance

Electrical heating in hazardous areas should only be used for its intended purpose and as per manufacturer’s instructions. Sometimes, EX certified products have conditions stipulated for their safe use. An X on the certificate number references this.

It is the duty holders’ responsibility to ensure these special conditions are taken into consideration. For example, an immersion heater may require to be fully immersed at all times during operation. In order for a duty holder to guarantee this, they would need to consider installation of low level monitoring in the tank to ensure the heater remained switched off if it was not fully immersed.

Installation Of Electric Heaters In Hazardous Areas

Inspection of heaters should be carried out on receipt of goods to ensure no damage has occurred during transit.

Before installation, insulation resistance tests should be carried out on the heating elements and the IR reading should be above acceptable value as stipulated by the manufacturer. This value will be clearly stated in the O&M literature.

Insulation Readings

💡 TIP – low insulation readings (IR) are often due to moisture in the enclosure terminal or in the heating elements. Silica gel packs can be used to draw out any moisture and the IR test should be repeated after 24hrs.

Electrical heating in hazardous areas should only be installed in the orientation intended. For example, horizontal immersion heaters should not be installed vertically. We have seen examples of clients mounting heaters, such as the FWDT, vertically as space did not permit horizontal mounting.

Space heaters should never be covered and airflow should not be restricted as it could prevent natural convection. Ambient temperatures should never exceed the safe working temperatures stipulated by the manufacturer.

Maintenance of Electric Heaters

Ensure the risk of flammable atmosphere is removed before any maintenance work is carried out. Electrical heating equipment where elements are exposed (space heaters) should be regularly checked for accumulation of dust which should always be removed.

Equipment should always be fully isolated before any work commences.

Only Manufacturers parts should be used for any repairs. Use of non-approved parts would invalidate any EX hazardous area certification.

Inspections should be routinely carried out 3 monthly, 6 monthly and annually. Manufacturers O&M manual will provide the necessary checks which should be carried out at each inspection.

For detailed guidelines on inspection and maintenance of electrical apparatus in explosive atmospheres, please refer to IEC/EN 60079-17.

  • IEC 60079-17:2013 Explosive Atmospheres – Part 17: Electrical Installations Inspection & Maintenance. 


  • IEC 60079-17:2013 applies to users and covers factors directly related to the inspection and maintenance of electrical installations within hazardous areas only, where the hazard may be caused by flammable gases, vapours, mists, dusts, fibres or flyings. 

How Can We Help?

For equipment sales and specification guidance about electrical heating in hazardous areas please contact T&D.

T&D are Process & Hazardous Area Heating experts with over 30 years’ experience serving petrochemical, oil and gas, utilities, food and beverage and pharmaceuticals.

Working in partnership with EXHEAT, we are able to offer a full range of electrical heating equipment which is certified for use in explosive atmospheres – this includes immersion heaters, air/space heaters, fan heaters, line heaters, water heaters, oil heaters and drum heaters.

Together we take our design responsibility seriously and help to provide our clients with the necessary information to ensure electrical heating in hazardous areas is safe, reliable and conforming to the required classifications.

Thorne & Derrick

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Further Reading