Hazardous Areas: The Complete Engineering Guide
A hazardous area — also called a classified location — is any place in an industrial facility where flammable gases, combustible dusts, or ignitable fibers may be present in sufficient concentration to cause a fire or explosion. Examples include oil and gas processing plants, chemical facilities, grain silos, pharmaceutical manufacturing areas, and paint spray booths. Hazardous areas are formally classified into zones (IEC system) or divisions (NEC system), based on the probability and duration of a flammable atmosphere being present. Equipment installed in these areas must carry Ex certification, and employers have legal obligations under ATEX (EU/UK), NEC (USA), or equivalent national regulations. This guide covers everything from zone classification and equipment selection through to legal obligations, inspection requirements, and training options — with links to detailed guides for each topic
FEATURED COURSES
Hazardous Area Classification
Hazardous Area Instrumentation
Intrinsic Safety Training Course
Hazardous Area Classification: The Two Systems
There are two international systems, used for Hazardous Area Classification. Which one to apply depends on your location, as the jurisdiction determines which of these two systems is accepted by regulators. We will take a brief look at both and later on you can study each one in more detail.
The NEC Class and Division System (US & Canada)
In the United States, the National Electrical Code (NEC for short) has been developed by the NFPA (National Fire Protection Association). NEC is also known as NFPA 70 and it uses Classes to define the type of flammable material present — Class I (gases/vapors), Class II (dusts) and Class III (fibers). Divisions define the probability of that material being present in the hazardous area. Division 1 areas have a flammable atmosphere under normal operating conditions; Division 2 areas have a flammable atmosphere only under abnormal conditions
such as equipment failure or leakage.
Class I, Division 2 is the most common classification in oil, gas, and petrochemical plants. Equipment must be listed for the specific Class, Division, and gas Group.
IEC Zone System (International, EU, Middle East, Asia)
The IEC 60079-10 standard uses Zones — Zone 0, 1, and 2 for gas/vapor atmospheres, and Zone 20, 21, and 22 for dust atmospheres. This three-level scale gives a finer gradation of probability than the NEC two-division approach.
Zone 0 is continuous flammable mixture presence; Zone 1 signifies intermittent presence of flammable mixtures and Zone 2 signifies that these explosive gas mixtures are present during abnormal conditions only.
Equipment in IEC-classified areas carries the Ex marking and must be certified to IEC 60079 standards. In the European Union, the ATEX Directives build on the IEC Zone system and add legal obligations for both manufacturers and plant operators.
Not sure which classification system applies to your facility?
The Abhisam Hazardous Area Classification course covers both NEC and IEC systems with real plant examples, zone extent calculations, and guidance on preparing hazardous area classification drawings.
Hazardous Area Equipment and the Ex Marking
Normal Industrial ( or Domestic/Commercial) electrical and mechanical equipment cannot be used in hazardous areas because it can act as an ignition source — through sparking contacts, hot surfaces, arcing, or static discharge. All equipment used in classified areas
must be specially designed and independently certified by notified bodies allowed to do so in that jurisdiction. This certified equipment carries the Ex marking.
Hazardous Area Instrumentation
Ex-rated Instrumentation is commonly referred to as Hazardous Area Instrumentation. It spans the full range of plant instrumentation and control equipment: pressure transmitters, temperature transmitters, flow meters, level gauges, level transmitters, solenoid valves, other specialized instrumentation such as density meters and viscosity meters, local HMI (Human Machine Interface) panels, gas chromatographs, analyzers, gas detectors, junction boxes, cable glands, handheld devices such as mobile phones and even CCTV cameras. and more.
Selecting the right Instrumentation requires matching three parameters: the protection concept (how ignition is prevented), the gas group or dust group (which materials are present), and the temperature classification (the maximum surface temperature the equipment can reach).
The easiest way to understand this is via the Abhisam Hazardous Area Instrumentation course
Explosion Protection Techniques- How Ex Equipment works
There is no single method for making equipment safe in a hazardous area. The IEC 60079 series defines over a dozen protection concepts, each using a different engineering approach. The choice of explosion protection method to be selected, depends on the zone or division, the type of material present, and the nature of the equipment. It also has to conform to the jurisdictional requirements of certification, labeling and other factors.
| Ex Code | Concept | How it prevents ignition | Suitable for |
|---|---|---|---|
| Ex d | Flameproof / Explosion-proof | Robust enclosure contains any internal explosion and cools escaping gases before they reach the surrounding atmosphere | Zone 1 / Div 1 |
| Ex e | Increased safety | No sparking parts inside; tighter tolerances prevent arcing under fault conditions | Zone 1 / Div 1 |
| Ex ia | Intrinsic safety (category a) | Circuit energy limited below the ignition energy of the gas; uses Zener barriers or galvanic isolators in the safe area | Zone 0, 1, 2 |
| Ex ib | Intrinsic safety (category b) | Same principle as Ex ia with lower protection level — one fault assumed rather than two | Zone 1, 2 |
| Ex p | Pressurisation / Purging | Enclosure pressurised with clean air or inert gas, preventing explosive atmosphere from entering | Zone 1, 2 / Div 1, 2 |
| Ex n | Non-sparking / Non-incendive | Equipment produces no sparks or hot surfaces in normal operation | Zone 2 / Div 2 |
| Ex m | Encapsulation | Ignition-capable components embedded in compound so they cannot contact the surrounding atmosphere | Zone 1, 2 |
| Ex o | Oil immersion | Equipment immersed in oil to prevent contact with explosive atmosphere | Zone 1, 2 — transformers |
Need to select the right Ex equipment for your installation?
The Hazardous Area Instrumentation course covers every protection concept with equipment selection examples, nameplate and label, marking reading, as well as installation and inspection rules.
Take a look at the Hazardous Area Instrumentation course details here . Watch the demo.
Temperature Classification and Gas Groups in Hazardous Areas
IEC versus NEC- Comparison table
Note: The below table, as well as other tables in this guide are only indicative of an approximate equivalence. You cannot directly install an NEC system certified equipment in an area that requires IEC or ATEX equipment, unless the same equipment is also certified for use in that jurisdiction. Always verify applicable standards with your local regulatory authority.
| IEC Group | NEC approx Equivalent | Typical gases | Sensitivity |
|---|---|---|---|
| Group IIA | Group D | Propane, methane, petrol vapour, natural gas | Least sensitive — lowest protection required |
| Group IIB | Group C | Ethylene, cyclopropane | Intermediate |
| Group IIC | Groups A & B | Hydrogen, acetylene, carbon disulfide | Most sensitive — highest protection required |
Equipment rated for Group IIC is safe for IIB and IIA atmospheres. The reverse is not true — never install Group IIA equipment in a Group IIC atmosphere.
Temperature Classification
The maximum surface temperature of the equipment is an important parameter to be considered. The temperature classification does this. It ensures that the surface temperature of the equipment is not enough to cause auto ignition of the materials present in that area.
| T-Class | Max surface temperature | Example gases requiring this class or lower |
|---|---|---|
| T1 | 450°C | Acetone, ammonia, methane |
| T2 | 300°C | Ethanol, hydrogen sulfide, n-butane |
| T3 | 200°C | Petrol/Gasoline, diesel vapor, jet fuel |
| T4 | 135°C | Acetaldehyde, diethyl ether |
| T5 | 100°C | Ethyl nitrite |
| T6 | 85°C | Carbon disulfide- lowest autoignition temperature of common industrial gases |
A nameplate reading Ex d IIB T4 means: flameproof enclosure, suitable for Group IIB gases and below, maximum surface temperature 135°C. Always verify all three parameters — protection concept, gas group, and T-class — match the specific gas present before installing any equipment.
Combustible Dusts in Hazardous Areas
Combustible dust is one of the most underestimated explosion hazards in industry. Unlike flammable gas, which is invisible and immediately associated with explosion risk, dust looks inert — it sits on surfaces, collects in corners, and is easy to ignore. Yet sugar, grain, coal, aluminum powder, and dozens of other common industrial materials can produce explosions that are as powerful and destructive as any gas explosion. The Imperial Sugar disaster (14 fatalities, 2008) and the Hayes Lemmerz aluminum dust explosion (2003) are reminders of what happens when dust hazards are not classified and controlled.
The IEC and ATEX systems classify dust hazardous areas using a parallel Zone system to the gas Zones, numbered 20, 21, and 22. These are often omitted from hazardous area programs at facilities that focus only on gas and vapor hazards — a compliance gap that regulators and insurers increasingly scrutinize.
Why Dust Explosions Are More Complex Than Gas Fires
A gas or vapor fire requires three conditions — the classic Fire Triangle. A dust explosion requires five. The two diagrams below show exactly which conditions are shared and which two additional conditions make dust explosions harder to prevent.
The Dust Zone System
| Zone | Definition | NEC approx Equivalent | Typical locations |
|---|---|---|---|
| Zone 20 | Explosive dust cloud present continuously, for long periods, or frequently in normal operation | Class II, Division 1 (continuous) | Inside dust-handling equipment: silos, hoppers, conveyors, dust collectors, mill interiors |
| Zone 21 | Explosive dust cloud likely to occur occasionally in normal operation | Class II, Division 1 (intermittent) | Areas around filling and emptying points, near dust-handling equipment where leakage can occur |
| Zone 22 | Explosive dust cloud not likely in normal operation; if it does occur, only briefly — or where dust layers may accumulate | Class II, Division 2 | Areas where abnormal leakage could produce a dust cloud; areas with dust layer accumulation on surfaces |
The Five Conditions — Dust Explosion Pentagon
Remove any single condition and the explosion cannot occur. This is the basis of all dust explosion prevention strategies:
- Combustible dust — the fuel source (sugar, aluminum, grain, coal, flour)
- Suspended dust particles — the dust must be dispersed in air at sufficient concentration to form an explosive cloud. Settled dust on surfaces is far less hazardous than the same dust suspended in air.
- Oxygen — normal air is sufficient; very high dust concentrations can actually smother an explosion if oxygen is excluded
- Ignition source — spark, hot surface, electrostatic discharge, friction, or mechanical impact
- Enclosed space — an enclosure that allows pressure to build rapidly. Without confinement, burning dust disperses and the pressure wave does not develop. With confinement, even a modest dust cloud can produce catastrophic overpressure.
Industries and Dust Types
| Industry | Typical combustible dust | IEC Dust Group | Notes |
|---|---|---|---|
| Grain / flour milling | Wheat, corn, barley dust | Group IIIB | Historically the most common dust explosion industry |
| Sugar refining | Sugar dust | Group IIIB | Imperial Sugar 2008 — highly explosive when suspended |
| Coal mining / handling | Coal dust | Group IIIB | Group I equipment also applies in underground mining (methane + coal dust combination) |
| Metal manufacturing | Aluminum, magnesium, titanium powder | Group IIIC (most sensitive) | Hayes Lemmerz 2003 — metal dusts require the highest protection level |
| Pharmaceuticals | Active ingredient powders, excipients | Group IIIB / IIIC | Frequently overlooked in ATEX programs — strict regulatory focus post-2010 |
| Wood / biomass | Wood dust, biomass pellet dust | Group IIIA | Increasing prevalence with biomass energy — many facilities not yet compliant |
Dust Groups vs Gas Groups
The IEC dust group system uses different letter designations from the gas group system — an important distinction when specifying equipment for a classified area:
| IEC Dust Group | Description | Typical materials | Sensitivity |
|---|---|---|---|
| Group IIIA | Combustible flyings (fibers and flyings) | Wood shavings, cotton fibers, textile flyings | Least sensitive |
| Group IIIB | Non-conductive dust | Grain, sugar, coal, flour, plastic powder | Intermediate |
| Group IIIC | Conductive dust (electrically conducting) | Aluminum, magnesium, zinc, carbon black | Most sensitive — highest protection required |
Equipment rated for Group IIIC is suitable for all dust groups. Equipment rated for Group IIIA is not suitable for Groups IIIB or IIIC. Always verify the dust group on equipment nameplates matches the dust present at your facility.
Key Standards for Combustible Dust
- IEC 60079-10-2 — Classification of areas where explosive dust atmospheres may occur
- IEC 60079-31 — Equipment protection by enclosure "t" for dust atmospheres
- NFPA 652 — Fundamentals of combustible dust (USA)
- NFPA 654 — Prevention of fire and dust explosions from combustible particulate solids (USA, general industry)
- NFPA 61 — Agricultural and food processing facilities (USA)
- EN 14460 — Explosion-resistant equipment (EU)
Hazardous Area Standards, Laws and Regulations
Hazardous area work is governed by national laws, national and international standards, and regional directives. The applicable framework depends entirely on where your facility is located.
United States
NFPA 70 (NEC)
Articles 500–516 cover Class/Division classification, equipment selection, and wiring methods. Enforced through state electrical codes.
International
IEC 60079 Series
30+ parts covering zone classification, equipment construction, installation, inspection, and maintenance. The global technical baseline.
European Union
ATEX Directives
Directive 2014/34/EU (equipment manufacturers) and 1999/92/EC (employer obligations). Mandatory in EU. Requires Explosion Protection Documents.
International
IECEx Scheme
Voluntary certification accepted in 50+ countries. Based on IEC 60079. Simplifies global equipment procurement alongside ATEX.
Canada
CSA C22.1
Canadian Electrical Code. Similar to NEC with some differences in equipment approval. CSA certification required for Canadian installations.
UK (post-Brexit)
DSEAR / UKEX
Dangerous Substances and Explosive Atmospheres Regulations 2002. UKEX marking replaced CE/ATEX post-Brexit. Technically aligned with ATEX. Northern Ireland continues to recognize EU CE and ATEX markings
Australia / NZ
AS/NZS 60079
Adopts IEC 60079 series directly. IECEx certification widely accepted without further national certification in most cases.
India
BIS / IS Standards
Bureau of Indian Standards adopts IEC 60079 as IS/IEC 60079 series. Equipment for petroleum installations also requires PESO (Petroleum and Explosives Safety Organization) approval.
Employer obligation: In most jurisdictions it is the legal responsibility of the plant owner/operator (Asset Owner of the facility) — not just the equipment supplier — to classify hazardous areas, document the classification, select appropriate equipment, train workers, and maintain Ex equipment. Failure to comply can result in criminal liability following an incident.
Major Hazardous Area related accidents
The standards and practices that govern hazardous areas today got largely developed to today’s versions, in response to catastrophic incidents. Understanding what went wrong — and what changed as a result — is as important as knowing the technical rules. Below are some infamous accidents related to Hazardous Areas.
Texas City Refinery Explosion — USA, 2005
15 workers killed, 180 injured. A raffinate splitter tower was overfilled during start-up, creating a vapor cloud that ignited from a running vehicle engine in an inadequately classified area. Led to fundamental changes in OSHA PSM enforcement and process safety culture.
Imperial Sugar Dust Explosion- USA, 2008
A huge explosion and fire occurred at the Imperial Sugar refinery near Savannah, Georgia, causing 14 deaths and injuring 38 others. This was one of the worst dust explosions in history. Many people were surprised that a seemingly safe material like sugar could cause such a huge explosion, damage to equipment and fatalities..
Bncefield Explosion — UK, 2005
Largest peacetime explosion in UK history. A storage tank was overfilled, creating a massive vapor cloud that ignited. 43 injuries, hundreds of millions in property damage. Resulted in major revisions to zone extent calculations for large storage tanks.
Aluminum Dust Explosion- USA,
On October 29, 2003, a series of explosions severely burned two workers, injured a third, and caused property damage to the Hayes Lemmerz manufacturing plant in Huntington, Indiana.The plant plant manufactured cast aluminum automotive wheels, and the explosions were fueled by accumulated aluminum dust, a flammable byproduct of the wheel production process.
These incidents share a common cause: inadequate hazardous area classification, equipment selection, or workforce training. Formal training and certification from Abhisam exists to prevent such incidents.
Gas Monitors- Gas detection and monitoring
Hazardous Area Classification only designates certain areas as hazardous. Hence, even in correctly classified and equipped areas, leaks can occur. A fixed gas detection system is the last active line of defense — it monitors the atmosphere continuously, triggers alarms when flammable gas concentrations approach dangerous levels (typically set at 20% of the Lower Explosive Limit, or LEL), and initiates automatic shutdowns at critical levels.
Gas detectors used in hazardous areas are themselves Ex-certified. They come in catalytic bead (pellistor), infrared (IR), photoionization (PID), and electrochemical types, each suited to different gases and concentration ranges. Workers entering classified areas carry portable personal monitors that typically detect flammable gas, hydrogen sulfide (H₂S), carbon monoxide (CO), and oxygen depletion simultaneously.
Free Hazardous Area Training Course and Mock Test
Take this free Hazardous Area basic training course.
Hazardous Area Classification training course
Comprehensive Hazardous Area Classification certification course.
Covers concepts of hazardous areas in detail including NEC and IEC, hazardous area zone extent calculations with samples, case study with sample hazardous area classification drawings
Hazardous Area Instrumentation training course
Compehensive Hazardous Area Instrumentation Certification course. Covers IEC and NEC standards, all protection methods including explosionproof, Increased Safety, Pressurization, Purging, Intrinsically safe systems and more.
Intrinsic Safety Training course
Comprehensive Intrinsic Safety training course that covers all aspects of designing Intrinsically Safe loops including understanding how IS circuits work, reading IS drawings, galvanic isolator and zener barrier selection, making entity calculations and carrying out inspections.
Free Download: Hazardous Areas Quick Reference Guide (Coming Soon)
A concise PDF covering: NEC Class/Division vs IEC Zone equivalence,
protection concepts at a glance, gas group and T-class quick reference, and key standards by region. Used by engineers on project sites worldwide.
Contact Us to get early access.
Non Electrical Equipment in Hazardous Areas
A widespread and dangerous misconception in hazardous area management is that only electrical equipment needs Ex certification. In reality, mechanical and non-electrical equipment can be just as capable of causing ignition — through hot surfaces, friction sparks, impact sparks, static electricity generated by moving parts, and adiabatic compression. Pumps, compressors, fans, conveyor systems, valves, actuators, and even hand tools all represent potential ignition sources if not properly assessed and controlled.
Under the ATEX Equipment Directive (2014/34/EU) and the IECEx scheme, non-electrical equipment intended for use in hazardous areas must comply with standards ISO 80079-36 (general requirements) and ISO 80079-37 (protection concepts). These standards require manufacturers to perform an Ignition Hazard Assessment (IHA) — a systematic evaluation of every potential ignition mechanism the equipment could produce under normal operation, expected malfunction, and rare malfunction conditions.
The protection concepts available for non-electrical equipment include:
- Constructional safety “c” — design measures that prevent ignition sources from occurring (e.g. limiting surface temperatures, eliminating sparking contacts)
- Control of ignition sources “b” — monitoring systems that detect and respond to potential ignition conditions
- Flow-restricting enclosure “fr” — enclosures that restrict the flow of explosive atmosphere to the ignition source
- Liquid immersion “k” — submerging ignition-capable components in protective liquid
- Pressurisation “p” — also applicable to non-electrical equipment to prevent explosive atmosphere from reaching ignition sources
Under ATEX, most non-electrical equipment for Zone 2 / Category 3 is covered by manufacturer self-declaration rather than third-party certification. However, equipment intended for Zone 1 / Category 2 or Zone 0 / Category 1 requires independent assessment. The manufacturer must lodge a technical file including the Ignition Hazard Assessment with an ATEX Notified Body and maintain it for ten years.
For plant operators, the key practical obligation is to verify that all equipment — not just electrical and instrumentation — carries appropriate ATEX or IECEx certification for the zone in which it is installed. This includes seemingly innocuous items such as pneumatic conveying systems, mechanical seals, bearing assemblies, and ventilation fans. A pump installed in a Zone 1 area without Ex certification is as much a compliance failure — and safety risk — as an uncertified motor.
What is an Explosion Protection Document (EPD)?
The Explosion Protection Document is one of the most important — and most frequently neglected — legal requirements for facilities with hazardous areas in the European Union and United Kingdom. Under ATEX Directive 1999/92/EC (implemented as DSEAR in the UK), every employer whose workplace contains areas where explosive atmospheres may occur is legally required to produce and maintain an EPD before the workplace is first used, and to update it whenever significant changes are made.
The EPD is not a single form or a checklist — it is a structured document that brings together the complete explosion safety picture for a facility. At a minimum it must contain:
- Explosion risk assessment — identification and assessment of all sources of flammable materials, grades of release, and ignition sources present
- Hazardous area classification drawings — the zone drawings showing Zone 0, 1, and 2 (or Zone 20, 21, 22 for dust) boundaries across the facility
- Equipment register — a list of all equipment installed in classified areas, with their ATEX/IECEx certification details, category, and gas group
- Ignition source register — identification of all potential ignition sources and the controls in place to prevent them from becoming effective
- Organisational measures — permit-to-work procedures, training records, contractor coordination arrangements, and emergency response provisions
- Verification statement — confirmation by a competent person that the overall explosion safety of the workplace is adequate before first use
The EPD must be reviewed and updated whenever a significant modification is made to the facility — new equipment, process changes, different materials, modifications to ventilation, or changes to building layout. A static EPD that has not been updated to reflect plant changes is a compliance failure and provides no legal protection in the event of an incident investigation.
Who is Responsible for the EPD?
The EPD is the responsibility of the employer — not the equipment supplier, not the installer, and not the ATEX certification body. In practice, many organisations commission external consultants to prepare the initial EPD, but the legal obligation rests with the plant operator. In the event of an explosion incident, the absence of or inadequacy of an EPD is almost always the first thing regulators examine.
ATEX and DSEAR: What Employers Are Legally Required to Do
The ATEX Worker Directive (1999/92/EC), implemented as DSEAR in the UK and equivalent regulations in other EU member states, places a specific set of legal duties on employers whose workplaces contain or may contain explosive atmospheres. These are not voluntary best practices — they are statutory obligations enforceable by national regulators, with criminal liability attaching to employers in the event of non-compliance that results in an incident.
The five core employer obligations are:
- Assess the explosion risks — carry out a structured assessment of all flammable and explosive materials present, their sources of release, likely concentrations, and the ignition sources that could make them effective. This assessment forms the foundation of the Explosion Protection Document.
- Classify hazardous areas into zones — based on the risk assessment, formally classify and document the extent and type of each hazardous zone (Zone 0, 1, 2 for gas; Zone 20, 21, 22 for dust). Produce and maintain hazardous area classification drawings.
- Select appropriate equipment by zone and category — ensure all equipment installed in classified areas is certified for the correct zone (Category 1 for Zone 0, Category 2 for Zone 1, Category 3 for Zone 2) and appropriate gas group and temperature class. This applies to both electrical and non-electrical equipment.
- Produce and maintain the Explosion Protection Document (EPD) — compile the EPD before the workplace is first used; ensure a competent person verifies overall explosion safety; update the EPD whenever significant plant changes are made.
- Train workers and coordinate contractors — ensure all workers in or near hazardous areas receive appropriate information, instruction, and training. Put in place arrangements for coordinating the work of contractors and visitors who may introduce ignition sources into classified areas. Mark classified areas with appropriate warning signs at entry points.
The relationship between zones, equipment categories, and the level of protection required is summarised below:
| Zone (gas) | Zone (dust) | ATEX Category | EPL | Protection level required |
|---|---|---|---|---|
| Zone 0 | Zone 20 | Category 1 | Ga / Da | Very high — safe even with two independent faults |
| Zone 1 | Zone 21 | Category 2 | Gb / Db | High — safe even with one foreseeable fault |
| Zone 2 | Zone 22 | Category 3 | Gc / Dc | Enhanced — safe in normal operation only |
Inspection and Maintenance of Ex Equipment (IEC 60079-17)
Installing certified Ex equipment in a classified area is the beginning of the compliance obligation, not the end of it. Ex equipment must be inspected and maintained throughout its operational life to ensure that the special features that make it safe — the flameproof gaps, the sealed enclosures, the intrinsically safe barriers, the pressurisation systems — remain intact and effective. Equipment that has been damaged, improperly repaired, or inadequately maintained can lose its explosion protection entirely while appearing superficially undamaged.
IEC 60079-17 (Explosive Atmospheres — Part 17: Electrical Installations Inspection and Maintenance) defines the requirements for the ongoing inspection and maintenance of Ex electrical installations. It specifies three grades of inspection, each with different scope and frequency:
| Inspection grade | What it involves | Who performs it | Typical frequency |
|---|---|---|---|
| Visual inspection | Check for obvious damage, missing bolts, unauthorized modifications, dust accumulation — without opening enclosures | Trained operative | Continuous or frequent — during routine plant rounds |
| Close inspection | All visual checks plus detailed examination of enclosures, cable entries, seals, and fixings — without live testing or dismantling | Competent person | Periodic — typically 1 to 3 years |
| Detailed inspection | All close inspection checks plus opening enclosures, testing, and verifying internal components against original certification requirements | Highly competent person — IECEx or CompEx certified | Periodic — maximum 3 to 4 years |
Common Inspection Failures
Most common inspection failures found in practice:
- Missing or incorrectly torqued flameproof enclosure bolts
- Cable glands not correctly installed or sealed
- Dust accumulation on equipment surfaces exceeding the 5mm layer limit
- Unauthorised replacement of Ex-certified lamp with standard lamp in an Ex luminaire
- Corrosion of enclosure surfaces compromising the flameproof joint
- Conduit seals (compound seals) not filled or incorrectly filled
Frequently Asked Questions about Hazardous Areas (Classified Locations)
Any industry handling flammable gases, flammable liquids, combustible dusts, or ignitable fibers. The most common are oil and gas (upstream, midstream, downstream), petroleum refining, chemical and petrochemical manufacturing, pharmaceutical production (solvents), paint and coatings, grain handling, flour milling, sugar processing, coal mining, and metals powder processing. Even food processing and woodworking facilities can have classified areas.
Explosion proof and Flameproof equipment use a robust heavy enclosure to contain any internal explosion and cool escaping gases before they can ignite the surrounding atmosphere. On the other hand, Intrinsically safe (Ex ia/ib/ic) takes a completely different approach — it limits the electrical energy in the circuit to a level too low to ignite the gas in the first place. Intrinsic safety is most common for low power devices such as instrumentation (transmitters, sensors) and mobile phones. Explosionproof is more common for motors, lighting, and switchgear. Intrinsically safe Ex ia is the only technique suitable for Zone 0.
The correct term for equipment suitable for hazardous areas is “explosion-protected”. Explosionproof is just one method of protection. There are many other methods of protection for equipment used in hazardous areas. They include methods such as Intrinsic Safety, Increased Safety, Pressurization & Purging and more. The method depends on the Hazardous Area classification and the type of equipment used.
No you don’t. ATEX is a legal requirement only within the European Union. Outside the EU, you need equipment certified to the relevant national or international standard — IEC 60079 in most of the world, NEC in the US, CSA in Canada, AS/NZS in Australia, IS in India. Many manufacturers obtain both ATEX and IECEx certification simultaneously, so the same equipment can be used globally. Check which scheme is mandated in your jurisdiction before purchasing anything. Do not assume that just because an equipment has been certified, it is suitable. Check your local laws and regulations for approvals.
Not automatically. While Class I Division 2 and Zone 2 represent similar conditions, equipment approved under one system is not automatically valid under the other. Equipment with dual NEC and IECEx/ATEX certification can be used in either. NEC Article 505 does allow Zone-rated equipment as an alternative in US installations under specific conditions, but single-certified equipment requires verification by a qualified engineer before installation.
Classifications must be reviewed whenever there is a significant plant change — new equipment, different process materials, modified ventilation, or changes to building layout. Additionally, a periodic review (commonly every 5 years) is recommended as good practice regardless of changes. ATEX regulations require operators to maintain an up-to-date explosion protection document (EPD). Failure to update classifications after plant modifications is consistently one of the top findings in incident investigations.
No, even mechanical equipment has to be of a special type before being used in hazardous areas. This is because mechanical sparking and hot surfaces are also sources of ignition in hazardous areas. These are considered non electrical equipment in hazardous areas that are subject to constraints in their design and installation. Under the ATEX Equipment Directive (2014/34/EU) and the IECEx scheme, non-electrical equipment intended for use in hazardous areas must comply with standards ISO 80079-36 (general requirements) and ISO 80079-37 (protection concepts). These standards require manufacturers to perform an Ignition Hazard Assessment (IHA) — a systematic evaluation of every potential ignition mechanism the equipment could produce under normal operation, expected malfunction, and rare malfunction conditions.