Ex d, Ex e, and Ex p: How to Choose the Right Explosion Protection Concept for Your Project

If you are specifying electrical equipment for a classified hazardous area on a UAE Oil & Gas, Petrochemical, or Offshore project, one of the first engineering decisions you will face is choosing the correct explosion protection concept. The IEC 60079 series defines over a dozen protection methods but in practice, the vast majority of UAE industrial projects are resolved using one of three: Ex d (flameproof), Ex e (increased safety), or Ex p (purging and pressurisation).

Ex d vs Ex e vs Ex p

Each concept works differently, applies to different equipment types, and carries different implications for cost, maintenance, and compliance. Selecting the wrong one or applying a Zone 2 concept to a Zone 1 area can result in project rejection, third-party inspection failure, and in the worst case, a safety incident. This guide explains how each concept works, when it is the right choice, and the most common mistakes engineers and procurement teams make when specifying Ex equipment for UAE projects.

What is an Explosion Protection Concept?

Before comparing the three concepts, it is worth clarifying what they actually do. An explosion protection concept is the engineering method used to prevent an electrical component from becoming an ignition source in an explosive atmosphere. The IEC 60079 series (and its ATEX equivalent) defines each concept, specifies how it must be designed and tested, and assigns it to one or more Equipment Protection Levels (EPLs) that determine which hazardous area zones it can be used in.

The concept you choose depends on four factors: the zone classification of the installation area (Zone 0, 1, or 2), the gas group of the flammable substance present (IIA, IIB, IIB+H2, or IIC), the required temperature class (T1–T6), and the type of electrical equipment being installed. Getting these four inputs right before selecting a protection concept is the most important step in the specification process.

Ex d Flameproof Enclosure (IEC 60079-1)

How it works: The Ex d concept does not prevent an explosive atmosphere from entering the enclosure. Instead, it assumes an internal explosion will occur and designs the enclosure to contain it. The enclosure walls are heavy-duty and precision-machined to withstand the internal explosion pressure, and the flame paths the controlled gaps at joints and cable entries are designed to cool escaping hot gases below the ignition temperature of the surrounding atmosphere before they exit. The explosion is contained; the surrounding atmosphere never ignites.

Applicable standard: IEC 60079-1. Equipment Protection Level Gb suitable for Zone 1 and Zone 2. With EPL Ga certification, can be used in Zone 0 (though rare for panels).

When to specify Ex d

• Motor starters, contactors, and DOL starters in Zone 1 any equipment where switching contacts will arc under normal operation
• Distribution boards and feeder panels in Zone 1 where internal arcing under fault conditions is a design assumption
• Local control stations with pushbuttons and selector switches in Zone 1
• Junction boxes containing relays, terminal blocks rated above Ex e limits, or electronic components
• Flameproof motors and luminaires in Zone 1 hazardous locations
• Any equipment in gas group IIC (hydrogen, acetylene) Ex e is not always available for IIC, Ex d provides the widest gas group coverage

Ex d practical considerations for UAE projects

• Enclosures are heavy cast aluminium or stainless steel construction adds significant weight to skids and offshore structures
• Every cable entry must use a certified Ex d gland matched to the enclosure volume and gas group standard compression glands are not acceptable
• Flame paths (machined joint faces, shaft seals) must never be painted or damaged a common site installation error that voids the certification
• IP66 is standard minimum for UAE outdoor applications verify this on the enclosure certificate, not just the manufacturer datasheet
• BARTEC, R.Stahl, and Pepperl+Fuchs are the preferred enclosure brands for ADNOC and major UAE operator approved vendor lists

Ex e Increased Safety (IEC 60079-7)

How it works: Unlike Ex d, the Ex e concept aims to eliminate ignition sources entirely. Equipment certified to Ex e must not produce arcs, sparks, or excessive surface temperatures under either normal operation or defined fault conditions. This is achieved through enhanced construction: wider creepage and clearance distances between live parts, improved terminal designs that resist loosening under vibration, reinforced winding insulation, and more stringent IP ratings. The explosive atmosphere can enter the enclosure but there is nothing inside capable of igniting it.

Applicable standard: IEC 60079-7. Equipment Protection Level Gb suitable for Zone 1 and Zone 2.

When to specify Ex e

• Junction boxes used purely for cable termination where there are no arcing components inside, only terminals
• Terminal boxes, marshalling cabinets, and I/O junction boxes for instrument loops
• Increased safety motors (Ex eb) in Zone 1 widely used for pumps, fans, and compressors where the motor itself has no sparking contacts
• Lighting fittings in Zone 1 where fluorescent or LED sources are used without switching contacts in the hazardous area
• Conduit and cable entry systems where a sealed, non-arcing termination is required
• Distribution boxes where all circuits are protected by current limiting devices and no switching occurs inside the enclosure

Ex e practical considerations for UAE projects

• Significantly lighter than Ex d GRP Ex e enclosures are common for offshore marshalling junction boxes where weight is critical
• Terminal tightening torque and minimum cable cross-section are specified in the certificate these must be followed exactly during installation and are checked at FAT and SAT
• Ex e is not suitable for equipment that arcs in normal operation this is the most common misapplication on UAE projects
• For IIC gas group (hydrogen) applications, verify the certificate explicitly covers IIC not all Ex e products do
• A popular and cost-effective choice for the non-arcing portions of a larger Ex d panel the terminal compartment is often Ex e while the switching compartment is Ex d

Ex p Purging and Pressurisation (IEC 60079-2)

How it works: Ex p takes a fundamentally different approach. Rather than designing the equipment to contain an explosion or eliminate ignition sources, Ex p prevents the explosive atmosphere from entering the enclosure in the first place. This is achieved by maintaining a positive internal pressure typically 5 to 15 mbar above the surrounding atmosphere using clean instrument air or nitrogen. Before the panel can be energised, an automated pre-purge cycle removes any explosive atmosphere from the enclosure interior. A purge controller continuously monitors internal pressure and automatically de-energises the panel (for Type X purge) or raises an alarm (for Type Y/Z) if pressure drops below the setpoint.

Applicable standard: IEC 60079-2. The purge type (X, Y, or Z) determines the Equipment Protection Level and the applicable zone.

Purge types at a glance

When to specify Ex p

• VFD (Variable Frequency Drive) panels in Zone 1 Ex p allows standard commercial drives (Siemens SINAMICS, ABB ACS, Schneider Altivar) to operate in Zone 1 without requiring the drive itself to carry an Ex d certificate
• PLC panels in Zone 1 full Siemens S7-1500 or S7-300 rack systems are impractical in sealed Ex d enclosures; Ex p provides the required access and thermal management
• Analyser shelters and sample conditioning systems in Zone 1 multiple analysers, heated sample lines, and calibration gas systems housed in a single pressurised assembly
• Large control panels where the heat dissipation of the internal equipment exceeds what can be managed in a sealed Ex d enclosure
• Equipment requiring regular access for maintenance or programming in Zone 1 Ex p can be opened after a verified purge cycle, unlike sealed Ex d

Ex p practical considerations for UAE projects

• Instrument air (or nitrogen) supply must be available, clean, dry, and at adequate pressure a single point of failure that must be risk-assessed
• The purge controller, pressure transducer, and solenoid valve are certified Ex equipment themselves and must be maintained as part of the system
• Commissioning documentation pre-purge test records, pressure decay tests, controller calibration certificates is mandatory and checked by third-party inspectors
• NFPA 496 governs purge systems on US-specification projects; IEC 60079-2 governs ATEX/IECEx projects ensure the correct standard is applied to your project specification
• Ex p is often more cost-effective than it first appears for VFD applications the saving on drive cost (standard vs. Ex-rated) frequently offsets the purge system capital cost

Quick Comparison Ex d, Ex e, Ex p

The Five Most Common Specification Mistakes on UAE Projects

1. Applying Ex e to equipment that arcs in normal operation. The most frequent error. Ex e terminals and enclosures are routinely installed in Zone 1 areas around contactors, motor starters, and relay panels equipment that arcs every time it operates. Ex e explicitly prohibits internal arcing under normal conditions. The correct solution is Ex d for the switching compartment with Ex e permitted for the terminal compartment only, or a full Ex d assembly.
2. Specifying Ex d without checking the gas group on the certificate. Not all Ex d enclosures cover gas group IIC. Many standard enclosures are certified to IIB+H2 which covers hydrogen applications but this is not the same as IIC. If your area classification identifies acetylene or other IIC gases, the certificate must explicitly state IIC. Substituting IIB+H2 for IIC without verification is a common compliance failure at third-party inspection.
3. Selecting the purge type based on cost rather than zone requirement. Type Z purging is the cheapest option but it is only valid for Zone 2 applications. Specifying Type Z for a Zone 1 location is a non-conformity that will be caught at ATEX/IECEx documentation review. For Zone 1, Type X (auto de-energise on pressure loss) is required where internal components are capable of causing ignition.
4. Using non-Ex cable glands with Ex d enclosures. The Ex d certificate for an enclosure applies to the complete assembly including all cable entries. Standard compression cable glands do not maintain the flameproof integrity of the enclosure. Every cable entry must use a certified Ex d gland matched to the enclosure certificate and the specific cable OD. A correctly assembled Ex d panel with a non-certified gland is no longer Ex d compliant even if the enclosure itself is certified.
5. Not confirming the temperature class against the process temperature. Equipment certified to T4 (maximum surface temperature 135°C) cannot be installed in an area where the process gas has an ignition temperature below 135°C. For UAE projects involving hydrogen sulfide (H2S), methane, or propane, T4 is typically adequate but for areas with low-ignition-temperature substances such as carbon disulfide (ignition temperature 90°C), T6-rated equipment is required. This must be confirmed against the area’s hazardous area classification dossier.