18.4 Hazardous Areas & Classified Zones
Key Takeaways
- EPC 28 requires awareness of hazardous area requirements and the standards referenced, not full hazardous area competence
- A hazardous area is one where flammable gas, vapour, mist, dust or fibres may be present in sufficient quantity to require special precautions
- Gas atmospheres are classified as Zone 0, 1 or 2 and dust atmospheres as Zone 20, 21 or 22, by how likely and how long an explosive atmosphere is present
- Equipment must be selected and installed to the explosion-protection technique appropriate to the zone, gas group and temperature class
- Additional formal training and, in many cases, a separate competency is required before working on hazardous area installations — a general electrical licence is not sufficient
Hazardous Areas & Classified Zones
Quick Answer: A hazardous area is one where a flammable atmosphere may be present. Areas are classified into zones by how likely and how long that atmosphere exists, and equipment must be selected to a matching explosion-protection technique, gas group and temperature class. A general electrical work licence does not authorise hazardous area work — additional training and competency are required.
What EPC 28 Actually Asks For
Read the capability carefully. EPC 28 requires knowledge of the AS/NZS 3000 requirements for hazardous areas and an awareness of the standards to which it refers, together with awareness of the additional training required to work competently there. It is a scope-and-awareness capability, not a licence to design a petrol station.
That distinction is itself examinable. The correct answer to "you are asked to install a light fitting in a spray booth" is not "select an IP66 fitting" — it is "this is a classified hazardous area; I need hazardous area competency and the area classification documentation before I do anything."
What Makes an Area Hazardous
An area is hazardous when a flammable atmosphere may be present in sufficient quantity to require special precautions for the construction, installation and use of electrical equipment. The three ingredients of ignition must be considered together: fuel (gas, vapour, mist, dust or fibre), oxygen, and a source of ignition — which in our trade means arcs, sparks and hot surfaces.
Typical locations:
| Location | Hazard |
|---|---|
| Petrol stations and fuel storage | Petrol vapour |
| Paint and spray booths | Solvent vapour and overspray |
| LPG storage and decanting | Flammable gas |
| Grain silos, flour mills, sugar handling | Combustible dust |
| Timber processing, textile mills | Combustible dust and fibres |
| Sewage and biogas plant | Methane and hydrogen sulfide |
| Battery charging rooms | Hydrogen |
| Some agricultural and mining operations | Gas and dust |
Battery charging rooms catch people out — a bank of flooded lead-acid cells on charge releases hydrogen, and hydrogen has a very wide flammable range.
Zone Classification
Gas, vapour and mist:
| Zone | Presence of explosive atmosphere |
|---|---|
| Zone 0 | Present continuously, or for long periods, or frequently |
| Zone 1 | Likely to occur in normal operation occasionally |
| Zone 2 | Not likely in normal operation, and if it does occur, will persist only for a short period |
Dust:
| Zone | Presence of combustible dust cloud |
|---|---|
| Zone 20 | Present continuously, or for long periods, or frequently |
| Zone 21 | Likely to occur in normal operation occasionally |
| Zone 22 | Not likely in normal operation, and only for a short period |
Classification is a documented engineering exercise producing a hazardous area classification drawing. An electrician does not classify an area by looking at it; the electrician reads the classification and installs to it.
Equipment Selection
Equipment for a hazardous area is selected by matching four things:
- Zone — determines the equipment protection level required.
- Gas group or dust group — the ignition characteristics of the specific substance.
- Temperature class — the maximum surface temperature must stay below the ignition temperature of the substance.
- Protection technique — the engineering method used.
Common protection techniques to recognise:
| Marking | Technique | Principle |
|---|---|---|
| Ex d | Flameproof | Contains any internal explosion and cools escaping gases |
| Ex e | Increased safety | No arcs or hot surfaces in normal operation |
| Ex i | Intrinsic safety | Energy limited below that needed for ignition (Ex ia, Ex ib) |
| Ex p | Pressurisation | Clean air or inert gas kept at positive pressure inside |
| Ex n | Type of protection "n" | For Zone 2, non-sparking in normal operation |
| Ex m | Encapsulation | Ignition-capable parts encased in compound |
An IP rating is not an explosion-protection rating. IP66 tells you about dust and water ingress; it says nothing about whether an internal arc can ignite the surrounding atmosphere. Confusing the two is a classic exam distractor.
Installation Discipline
- Use only the certified gland and entry for the equipment type — a flameproof enclosure loses its protection with the wrong gland.
- Maintain the specified flamepath dimensions; do not paint, machine or damage flanged joints on Ex d equipment.
- Do not substitute fasteners on Ex enclosures; the specified bolts are part of the certification.
- Intrinsically safe circuits must be segregated and identified (commonly light blue) and connected through the correct barrier or isolator.
- Maintain and record inspection regimes — hazardous area installations require initial and periodic inspection to the relevant standard.
- Never modify a certified assembly. Replacing a lamp with a different type, or adding a gland, can void the certification.
The Competence Boundary
The Wiring Rules refer out to the hazardous area standards for classification, selection, installation, inspection and maintenance. Working to those standards requires additional training beyond a Certificate III and an electrical work licence — typically a recognised hazardous area competency covering classification, selection, installation, inspection and maintenance.
The professionally correct position for a newly licensed electrician:
- Recognise when an area is or may be classified.
- Stop and obtain the classification documentation.
- Decline work that is beyond your competency and arrange a competent person.
- Never install ordinary equipment in a classified area on the basis that it "looks well sealed."
That answer — recognise, stop, escalate — is what EPC 28 is testing.
A gas atmosphere is present continuously or for long periods in a particular area. How is that area classified?
An electrician is asked to install a standard IP66 luminaire in a paint spray booth. What is the correct response?
Which explosion-protection technique works by limiting circuit energy below the level that could cause ignition?
Why is a battery charging room often treated as a hazardous area?