An explosion-proof fan certified Ex d IIC T4 is a fan built so that, even if flammable gas enters the enclosure and ignites inside, the flameproof (Ex d) housing contains the explosion and cools the escaping gases below the ignition point, while the IIC rating covers the most volatile gas groups and the T4 class caps surface temperature at 135°C. It is the required equipment for ventilation in hazardous areas such as petrochemical plants, solvent stores, paint booths, and battery rooms where Zone 1 or Zone 2 gas atmospheres may occur.
Understanding the Ex d IIC T4 Marking
The marking is a condensed safety specification. Ex d denotes flameproof enclosure construction: joints are precisely machined to a controlled gap and length so flames cannot propagate outward. IIC is the gas group with the widest ignition-energy range, including hydrogen and acetylene, so an IIC-rated fan is also valid for the less severe IIA and IIB groups. T4 is the temperature class limiting any exposed surface to 135°C maximum, which is safely below the auto-ignition temperature of most process gases. Together, Ex d IIC T4 is among the most demanding common ratings for flammable-gas duty.
How an Explosion-Proof Fan Is Built
Three design pillars make the fan safe. First, the motor is a certified flameproof unit with reinforced cast or welded enclosure, rated for the zone and temperature class, often with terminal boxes separately certified to Ex e (increased safety). Second, the impeller and casing use non-sparking materials such as aluminium-bronze or static-dissipative composites, and all rotating parts maintain controlled tip clearance to avoid contact and sparking. Third, the electrical supply enters through certified flameproof glands and conduit, and the whole assembly is grounded so static cannot accumulate. Typical units deliver 1,000 to 40,000 m³/h at static pressure up to 3,000 Pa, with motor power from 0.37 kW to 45 kW depending on duty.
Ex d vs Ex e vs Zone Classification
| Protection / zone | How it works | Typical use | Temperature limit |
|---|---|---|---|
| Ex d (flameproof) | Contains internal explosion, cools vent gas | Gas Group IIC, motors, fan housings | T1 to T6 as marked |
| Ex e (increased safety) | Prevents arcs and high surface temp | Terminals, lighting, aux equipment | T1 to T6 as marked |
| Zone 1 | Explosive atmosphere likely in normal operation | Near process vents, filling points | Equipment must suit zone |
| Zone 2 | Explosive atmosphere rare, short duration | Storage areas, secondary spaces | Equipment must suit zone |
Matching the protection type to the zone and gas group is the core of any hazardous-area ventilation design and must be confirmed by a risk assessment.
When to Choose Explosion-Proof Construction
- Choose Ex d IIC T4 when the area handles hydrogen, acetylene, or mixed unknown gases and surface temperature must stay below 135°C.
- Choose Ex d IIB T4 when only less volatile gases such as propane or gasoline vapors are present.
- Choose a lower temperature class (T3 at 200°C, T2 at 300°C) only if the gas auto-ignition temperature allows it, to reduce cost.
- Choose Ex e auxiliary components for terminal boxes and control gear in the same zone.
- Never install a standard industrial fan in any classified Zone 1 or Zone 2 location.
Certification and Installation Notes
The fan must carry third-party certification (such as ATEX EU or IECEx) stating the exact Ex marking, gas group, temperature class, and zone. The certificate and the installation must be documented in the facility's hazardous-area dossier. During installation, use only certified glands and conduit, maintain the specified flamepath gap, and verify grounding resistance stays below 1 ohm to earth. Periodic inspection, often every 12 to 24 months depending on the standard and environment, confirms the flamepaths, glands, and labels remain intact. Any field modification that breaks the certified enclosure voids the protection and is prohibited.
Keruite manufactures this equipment at an 80,000 m² facility in Dezhou, China, with an in-house AMCA-210-style test laboratory; every unit is balanced to G2.5 and performance-tested before shipment.
Material Selection and Spark Control
Beyond the Ex d enclosure, the internal airflow path must avoid ignition sources. Impellers are commonly cast in aluminium-bronze or built from static-dissipative composite so a blade tip cannot throw a ferrous spark, and tip clearance to the casing is held at 2 to 5 mm to prevent contact. Shaft seals use non-sparking grades, and any external fasteners are stainless or coated to keep the flamepath gap within the certified 0.1 to 0.2 mm. The motor terminal box is usually certified separately to Ex e, and all conduit entries use certified flameproof glands with the correct thread and seal. Surface temperature is verified across the whole frame, not just the motor, because the impeller and casing in Zone 1 can also reach the T4 limit of 135°C under stalled or blocked flow.
Lifecycle, Inspection, and Standards
Explosion-proof fans are inspected on a fixed schedule, often every 12 to 24 months, with the interval set by the operating environment and the applicable standard such as ATEX 2014/34/EU or IECEx. Inspectors check the flamepath for corrosion or damage, confirm the glands are tight and grounded to below 1 ohm, and verify the Ex label and certificate number match the zone drawing. A fan serving hydrogen or acetylene (Group IIC) must never be downgraded to a IIB unit, and any field repair that breaks the certified enclosure voids the protection. Typical service life is 10 to 15 years with correct maintenance, and motors are rewound or replaced only by certified shops that restore the Ex rating. Keeping a marked-up hazardous-area dossier ensures the next inspection and any audit can confirm continued compliance.
Zone Drawing and Documentation
Every hazardous area needs a classified drawing showing Zone 1 or Zone 2 boundaries, the gas group, and the temperature class so the fan selection can be audited. The Ex d IIC T4 certificate, gland schedule, and grounding record form the compliance file that inspectors check, and any future process change that raises the gas group or temperature must trigger re-selection before operation.
FAQ
What does Ex d IIC T4 mean on an explosion-proof fan?
Ex d means flameproof enclosure, IIC is the gas group covering hydrogen and acetylene with the widest ignition-energy range, and T4 means the surface temperature stays at or below 135°C. Together they define a fan safe for the most demanding flammable-gas zones, certified to contain an internal explosion without igniting the surrounding atmosphere.
Where must an explosion-proof fan be installed?
It must be used in classified hazardous areas such as Zone 1 or Zone 2 for gases, typically petrochemical plants, paint booths, battery rooms, and solvent stores. The fan, motor, and all exposed parts must carry the correct Ex rating for the specific gas group and temperature class of the location.
Can I use a standard fan in a hazardous area if I add a spark-proof motor?
No. Explosion protection requires the whole airflow path, not just the motor, to be certified. A standard impeller can generate static sparks or reach unsafe surface temperatures, so only a fully certified Ex d or Ex e assembly with proper conduit and grounding may be used in hazardous zones.
What is the difference between Ex d and Ex e protection?
Ex d is flameproof: the enclosure contains an internal explosion and cools escaping gases below ignition temperature. Ex e is increased safety: it prevents arcs and raises insulation and clearance to avoid ignition in the first place. Ex d IIC T4 suits gas Group IIC, while Ex e is often paired for terminals and less severe duties.