Hazardous area risk considerations for heating systems
Managing risk in a classified area requires more than selecting certified equipment — it requires understanding where the risk actually sits and what controls address it.
Ignition in a hazardous area requires three things simultaneously: a flammable atmosphere, oxygen, and an ignition source. ATEX zone classification and equipment certification address the third element by controlling the ignition source — limiting surface temperatures and eliminating sparks and arcs within the zone. The first two elements are inherent to the environment. Zone classification acknowledges that the atmosphere will be present, at a frequency defined by the zone designation.
It is not simply a question of whether certified equipment is installed. It is a question of whether every component of the installed system — equipment, installation, control architecture and ongoing maintenance — maintains the controls that prevent the heating system from becoming an ignition source.
How heating systems can become ignition sources
A heating system can introduce ignition risk in several distinct ways. Each maps to a different control measure:
- Element surface temperature exceeding T-class limit. The most direct risk. Can result from: incorrect T-class specification for the substances present; element operating with insufficient product contact (dry run, low fill level, loss of medium); controller failure in call-for-heat state without independent over-temperature protection; or use of standard non-ATEX-rated equipment in a classified zone.
Control: Correct T-class selection; verified element watt density; dual temperature-limiting devices; dry-run protection where applicable. - Sparks or arcs from electrical components within the zone. Arcing at terminals, switching contacts, junction boxes or cable connections that are not constructed and certified to eliminate or contain arcing within the classified area.
Control: All electrical components within the zone rated to the appropriate category and protection concept (Ex d, Ex e, Ex ia, etc.); zone boundary crossings sealed with certified cable glands. - Mechanical sparks from moving parts. Relevant where pumps, motors or fans form part of a heated transfer system. Friction, impact and bearing failure are ignition mechanisms separate from electrical risk.
Control: ATEX-certified motors and drives; maintenance of bearing clearances and lubrication; inspection for wear. - Static electricity. Relevant in liquid transfer applications where non-conducting media flowing through pipework or hoses can accumulate static charge. Bonding and earthing of all conductive components connected to or near the heating and transfer system is required.
Control: Bonding and earthing scheme specified and installed to the requirements of the zone drawing; conductive or dissipative materials used for hose assemblies in ATEX zones. - Hot surfaces from non-electrical causes. Mechanical friction in bearings, brakes and couplings; hot-work in the vicinity of a classified area; or process exothermic reactions that raise ambient temperatures. These are managed through work permit and hot-work controls, not equipment certification.
Common failure modes in installed ATEX heating systems
Installation and operational experience identifies a consistent set of failure modes — not in equipment design, but in how systems are specified, installed and maintained:
- Zone drawing not consulted at specification stage. Equipment is selected based on the process requirement — heating power, temperature, vessel type — without reference to the zone classification of the installation location. The result is Category 3 equipment installed in a Zone 1 area, or a T-class that does not match the substances present.
- Non-rated control components within the zone. ATEX-certified heating elements installed with a standard commercial temperature controller located inside the zone boundary. The controller is the component most likely to introduce arcing (relay contacts, terminals) and is frequently the least attention is paid to during specification.
- Incorrect or missing cable glands. Zone boundary entries — power cables, sensor cables, conduit entries — fitted with standard PG-thread or NPT glands rather than glands certified for the protection concept of the enclosure. Most common finding at site inspections
Non-certified cable glands at zone boundary entries. An Ex d enclosure fitted with a standard unrated gland is no longer Ex d compliant — regardless of the enclosure's own certification.
- Safety cut-out not independent. Over-temperature protection implemented as a high-temperature alarm through the primary controller, rather than as a physically separate device in series. If the controller fails, the alarm fails with it.
- Auto-reset cut-out. A safety cut-out that resets automatically when temperature falls back within range. Functionally it may appear to work, but it defeats the purpose of the manual-reset requirement: a tripped cut-out should require human investigation before the system restarts.
- Unauthorised modifications. Post-installation changes to heater power, control setpoints, sensor locations or enclosure entries that were not assessed against the original certification and zone drawing.
Documentation, inspection and ongoing compliance
Compliance of an ATEX heating installation is a point-in-time condition that requires active maintenance. Three frameworks govern what is required after initial installation:
Initial inspection (IEC 60079-14). Before a new installation is energised, a documented inspection must verify that all equipment is certified for the zone; installation has been carried out in accordance with the zone drawing; protection concept requirements (gland specifications, enclosure entry sealing, intrinsically safe circuit segregation) are met; and bonding and earthing is complete. The initial inspection record forms part of the permanent installation documentation.
Periodic inspection (IEC 60079-17). Classified installations must be periodically inspected to verify that the installed system remains compliant. IEC 60079-17 defines three inspection grades — visual, close, and detailed — and provides guidance on inspection intervals. The interval depends on the zone classification, the equipment protection level and the operating environment. Typical intervals range from annually to every three years; installations in particularly aggressive environments or with a history of equipment degradation may warrant shorter intervals.
Any modification to an installed ATEX system — change in heating power, component replacement, change in process substance or zone boundary — must be assessed against the original certification and zone drawing before the modification is made. Undocumented modifications invalidate the installation record and may invalidate component certification.
Documentation that should exist for every installed ATEX heating system:
- Zone classification drawing, current revision, signed off by the responsible person
- Equipment schedule listing each certified item, its certificate number and ATEX marking
- Initial inspection record (IEC 60079-14)
- Periodic inspection records (IEC 60079-17), with dates and inspector details
- Modification and repair log, with assessment against certification basis for each entry
Related resources
Managing ATEX risk is less about individual components and more about system integrity — how heating elements, control systems and installation details interact under real operating conditions and degrade over time.
Risk managed at every stage — design, certification and documentation
HeatXperts approaches ATEX heating applications from the zone classification drawing inward — verifying T-class, gas group, control architecture and certification route before specifying equipment. Every system is delivered with the documentation required for a compliant installation and ongoing inspection record.
For sites with existing classified installations requiring review, assessment against current zone drawings, or replacement of non-compliant components, our engineers work from the installed condition outward.