Hazardous Area Equipment Marking Explained
Hazardous area equipment marking provides a standardised identification system that defines where equipment can be safely installed and how it achieves explosion protection. These markings are critical for correct equipment selection, compliance verification, inspection, and lifecycle maintenance.
This page explains:
- How hazardous area equipment is marked for gas and dust atmospheres
- The meaning of each marking element
- Differences between ATEX and IECEx
- How to interpret a complete marking string in a practical way
This reference is applicable to oil & gas, chemicals, power, utilities, mining, manufacturing, and infrastructure projects.
Governing Standards & Certification Frameworks
ATEX (European Directive)
- ATEX Directive 2014/34/EU (formerly 94/9/EC)
- Mandatory for equipment placed on the EU market
- Defines Equipment Groups and Categories
- Widely referenced in international EPC specifications
IECEx (International Scheme)
- Based on IEC 60079 series
- Voluntary but globally accepted certification system
- Commonly used in Middle East, Africa, and international projects
UL / FM (North American Practice)
- UL and FM approvals
- Often specified by insurers or US-origin operators
- May coexist with IECEx / ATEX in global projects
Functional Safety (SIL)
- IEC 61508 / IEC 61511
- Addresses risk reduction via safety functions
- Independent of hazardous area certification
Hazardous area marking addresses ignition prevention.
SIL addresses process risk reduction.
They are complementary, not interchangeable.
Structure of Hazardous Area Equipment Marking
A typical hazardous area marking string communicates five key things:
- Where the equipment can be used (Zone / Category / EPL)
- What type of atmosphere (Gas or Dust)
- How ignition is prevented (Ex protection concept)
- What substances it is suitable for (Gas / Dust group)
- Maximum surface temperature (Temperature class)
Equipment Groups (ATEX / IEC)
Group I
- Underground mining
Group II
- Surface industries (oil & gas, chemicals, utilities, power plants)
Group III
- Combustible dust atmospheres
Most industrial and infrastructure projects use Group II (Gas) and Group III (Dust) equipment.
Equipment Categories (ATEX)
| Category | Protection Level | Typical Zone |
|---|---|---|
| 1 | Very high | Zone 0 / Zone 20 |
| 2 | High | Zone 1 / Zone 21 |
| 3 | Normal | Zone 2 / Zone 22 |
Category defines where the equipment may be installed, not its construction method.
Equipment Protection Levels (EPL – IEC)
| EPL | Protection Level | Zone |
|---|---|---|
| Ga / Da | Very high | Zone 0 / 20 |
| Gb / Db | High | Zone 1 / 21 |
| Gc / Dc | Enhanced | Zone 2 / 22 |
EPL provides a risk-based IEC interpretation, often used in IECEx marking.
Gas Atmosphere Marking Explained
Typical Gas Marking Format
Ex ia IIC T4 Ga
Let’s break this down clearly.
Ex
Equipment is designed for explosive atmospheres.
Protection Concept
- ia → Intrinsic safety (highest level)
Other common gas protection types:
- Ex d – Flameproof enclosure
- Ex e – Increased safety
- Ex p – Pressurisation
- Ex ec – Enhanced safety (Zone 2)
Gas Group
- IIA – Propane
- IIB – Ethylene
- IIC – Hydrogen / acetylene (most severe)
Equipment certified for IIC can also be used in IIB and IIA atmospheres.
Temperature Class
Defines maximum surface temperature:
| Class | Max Surface Temp |
|---|---|
| T1 | 450°C |
| T2 | 300°C |
| T3 | 200°C |
| T4 | 135°C |
| T5 | 100°C |
| T6 | 85°C |
Surface temperature must be below the ignition temperature of the gas.
EPL (Gas)
- Ga → Suitable for Zone 0
- Gb → Zone 1
- Gc → Zone 2
Dust Atmosphere Marking Explained
Typical Dust Marking Format
Ex t IIIC T85°C Db
Ex t – Protection by Enclosure
- Prevents dust ingress
- Limits surface temperature
- Replaced older “Ex tD” terminology
Dust Group
- IIIA – Combustible flyings
- IIIB – Non-conductive dust
- IIIC – Conductive dust (most severe)
Maximum Surface Temperature
- Expressed directly in °C (e.g. T85°C)
- Must be below dust ignition temperature
EPL (Dust)
- Da → Zone 20
- Db → Zone 21
- Dc → Zone 22
Combined Gas & Dust Marking
Some equipment is certified for both gas and dust atmospheres.
Example:
Ex ia IIC T4 Ga / Ex t IIIC T85°C Db
Meaning:
- Intrinsically safe for hydrogen gas in Zone 0
- Protected for conductive dust in Zone 21
- Separate evaluation for gas and dust risks
Fully Worked Example (Easy & Practical)
Example Marking on a Field Gas Detector
II 2G Ex ia IIC T4 Gb
IECEx BVS 21.0019X
What This Means (Plain Language)
- II → Surface industry
- 2G → Category 2, Gas atmosphere (Zone 1)
- Ex ia → Intrinsically safe (highest protection)
- IIC → Suitable for hydrogen and all lesser gases
- T4 → Max surface temperature 135°C
- Gb → EPL suitable for Zone 1
- IECEx certificate → International certification
- “X” suffix → Special conditions of use apply (must be followed)
Result:
This detector can be safely installed in Zone 1 gas areas, and potentially Zone 0 depending on installation and certification details.
Quick-Reference: Hazardous Area Zone → Equipment Marking → Typical Products
Gas Atmospheres (IEC / ATEX)
| Hazardous Zone | Typical Marking (Indicative) | EPL | Typical Equipment / Products |
|---|---|---|---|
| Zone 0 | Ex ia IIC T4 Ga | Ga | Gas detectors, pressure & temperature transmitters, analytical sensors |
| Zone 1 | Ex d IIB/IIC T4 Gb Ex e IIB T3 Gb Ex ia IIC T4 Gb | Gb | Motors, junction boxes, lighting, control panels, valves actuators |
| Zone 2 | Ex ec IIB T3 Gc Ex nA IIA T3 Gc Ex p IIB T4 Gc | Gc | Control cabinets, field enclosures, analyzers, local panels |
Equipment certified for IIC may be used in IIB and IIA atmospheres.
Dust Atmospheres (IEC / ATEX)
| Hazardous Zone | Typical Marking (Indicative) | EPL | Typical Equipment / Products |
|---|---|---|---|
| Zone 20 | Ex t IIIC T85°C Da | Da | Level sensors, temperature probes, dust monitoring instruments |
| Zone 21 | Ex t IIIB/IIIC T85°C Db | Db | Motors, junction boxes, lighting, conveyor equipment |
| Zone 22 | Ex t IIIB T100°C Dc | Dc | Control panels, enclosures, instrumentation cabinets |
Dust surface temperature must always remain below dust ignition temperature.
ATEX Category vs Zone (Fast Cross-Check)
| ATEX Category | Gas Zone | Dust Zone | Typical Use |
|---|---|---|---|
| Category 1 | Zone 0 | Zone 20 | Continuous explosive atmosphere |
| Category 2 | Zone 1 | Zone 21 | Likely during normal operation |
| Category 3 | Zone 2 | Zone 22 | Infrequent / abnormal presence |
Typical Protection Concepts by Zone
| Protection Type | Common Zones | Typical Products |
|---|---|---|
| Ex ia | Zone 0, 1 | Sensors, transmitters, detectors |
| Ex d | Zone 1, 2 | Motors, junction boxes, panels |
| Ex e | Zone 1, 2 | Motors, terminals, lighting |
| Ex p | Zone 1, 2 | Analyzer shelters, cabinets |
| Ex ec / Ex n | Zone 2 | Panels, enclosures |
| Ex t | Zone 20/21/22 | Dust motors, enclosures |
Certification Body & Certificate Number
Markings include:
- Notified Body (ATEX) or Certification Body (IECEx)
- Certificate number and year
- Surveillance and audit reference
Suffix “X” or “U” indicates:
- X – Special conditions for safe use
- U – Component, not standalone equipment
Relationship Between Hazardous Area Certification & SIL
- Ex certification → Prevents ignition
- SIL certification → Ensures safety function reliability
Example:
- Gas detector:
- Ex ia → Safe in hazardous area
- SIL 2 → Reliable shutdown function
Both must be assessed independently.
InfraMENA Engineering Note
Hazardous area marking interpretation must always be aligned with:
- Area classification study
- Project specifications
- Authority Having Jurisdiction (AHJ)
- Local regulations and client requirements
InfraMENA supports engineering interpretation, documentation alignment, and compliant sourcing based on project-defined requirements.
Technical Disclaimer
This page is an engineering reference based on internationally recognised standards. Final equipment selection, installation, and acceptance remain subject to project specifications, applicable regulations, and AHJ approval.