What makes a compressor package “hazardous area”?
A compressor counts as hazardous-area equipment in two situations. Either it stands in a place where a flammable gas, vapour or dust atmosphere may be present, such as a refinery, gas plant, solvent store, paint shop, pharma solvent area or grain handling site; or it compresses a flammable gas itself, such as natural gas, biogas, hydrogen or a hydrocarbon process gas, which can create a hazardous area around the machine through leaks and vents.
In both cases, every possible ignition source on the package matters: electric motors, starters, variable-frequency drives, instruments, junction boxes, hot surfaces, sparks from mechanical contact, static electricity and, on diesel packages, the engine exhaust and air intake.
Start with the area classification
Area classification is the plant owner’s responsibility, normally carried out by a competent engineer following IEC 60079-10-1 for gases (and IEC 60079-10-2 for dusts). The compressor supplier does not classify your plant; the supplier needs the result.
| Zone | Meaning | Typical equipment category |
|---|---|---|
| Zone 0 | Explosive gas atmosphere present continuously or for long periods | Category 1 (EPL Ga); compressors are rarely placed here |
| Zone 1 | Likely to occur in normal operation | Category 2 (EPL Gb), e.g. flameproof Ex d motors |
| Zone 2 | Not likely in normal operation, and only briefly if it occurs | Category 3 (EPL Gc), e.g. Ex ec non-sparking motors, or higher |
| Zones 20, 21, 22 | Equivalent zones for combustible dust | Dust-rated equipment (EPL Da, Db, Dc) |
The classification dossier should also give the gas group and temperature class. Gas groups IIA (for example propane), IIB (for example ethylene) and IIC (hydrogen, acetylene) indicate how easily the gas ignites and how hard it is to contain a flame. Temperature classes T1 to T6 set the maximum surface temperature, from 450 °C for T1 down to 85 °C for T6; T3 is 200 °C and T4 is 135 °C.
Area classification is not equipment certification
These two are often confused. Classification describes the place. Certification describes the equipment and confirms it is safe in that type of place. In India, electrical equipment for hazardous areas normally needs the approvals required by the Petroleum and Explosives Safety Organisation (PESO), together with an IECEx or ATEX certificate where the specification calls for one. The package documents should list each certified item with its marking, for example “Ex db IIB T4 Gb”, and the certificate numbers.
Non-electrical parts matter too. ISO 80079-36 and -37 cover the ignition risk of mechanical equipment such as couplings, belts, fans and bearings. A package is only as safe as its least suitable component, so ask for a full ignition-hazard assessment of the package, not just a certified motor.
Define the package boundary precisely
Many hazardous-area problems arise at the edges of scope. Write down, item by item, who supplies and certifies:
- Main motor and its terminal box, or the diesel engine and its spark arrestor, exhaust temperature control and air-intake shut-off valve.
- Starter, soft-starter or VFD and where it is located; often in a safe-area MCC room.
- Instruments, solenoid valves, pressure switches, transmitters and their junction boxes.
- Control panel, PLC and any purged or pressurised enclosure.
- Cooling fans, heaters, lighting and auxiliary motors.
- Earthing, bonding and cable glands up to the termination point.
- Canopy or enclosure ventilation, gas detection and fire detection.
Temperature class and hot surfaces
A compressor generates heat. The discharge pipe, airend or cylinder, oil separator, aftercooler and engine exhaust can run well above the ignition temperature of some gases. For an oil-injected screw compressor, normal discharge temperature is about 75–95 °C, but the discharge piping and separator vessel may get hotter under fault conditions, and a reciprocating gas compressor stage can run considerably hotter. Diesel engine exhausts and turbochargers are very hot unless cooled or shielded.
The package must keep every exposed surface below the temperature-class limit in all credible states, including high ambient temperature. In the Indian summer, ambient air can exceed 45 °C in parts of Telangana and Andhra Pradesh, and that heat adds directly to surface temperatures inside an enclosure. High discharge temperature shutdowns, insulation or guarding, and cooling margins should be set with this in mind.
Motor, VFD and electrical interface
- Choose the motor protection type to suit the zone and gas group: Ex db (flameproof) for Zone 1, Ex eb (increased safety) where permitted, Ex ec for Zone 2.
- When a motor is driven by a VFD, the motor certificate must cover inverter operation; heating, bearing currents and voltage spikes change with VFD duty.
- Place the VFD, starter and PLC in a safe area where possible; otherwise use certified or purged enclosures.
- Instrument loops may be intrinsically safe (Ex i), which needs barriers or isolators and a loop calculation.
- Use certified cable glands matching the enclosure protection type, and a proper earthing and bonding scheme for the skid.
Mechanical ignition sources and static
Belts can build static charge and should be anti-static where belts are used at all. Cooling fans must not strike their shrouds; non-sparking fan materials may be specified. Couplings need guards that cannot rub. Bearings need condition monitoring because an overheating bearing becomes a hot surface. All metal parts of the skid, canopy and piping should be bonded and earthed, and flexible hoses should be conductive or bonded.
Intake, ventilation and gas detection
An air compressor in a hazardous area must not draw flammable vapour into its intake. Compressing a fuel–air mixture is dangerous. Pipe the intake from a safe location or confirm that the intake area is free of flammable atmosphere. For diesel compressors, fit an automatic air-intake shut-off valve so that a flammable gas drawn into the engine cannot cause overspeed.
Enclosures and compressor houses need ventilation enough to dilute small leaks, and gas detectors positioned for the gas density: high for hydrogen and methane, low for heavier vapours. The cause-and-effect chart should state what each detector level does: alarm, increase ventilation, stop the compressor, close isolation valves.
Process containment, venting and relief
When the compressor handles a flammable gas, venting becomes part of the hazardous-area design. Relief valves, seal vents, packing vents, purge lines and blowdown lines must discharge to a safe destination, such as a flare or vent stack, sized for the worst case. Our page on gas compressor seal and leakage management covers the seal side in detail.
Operating states: normal, start-up, upset and emergency
- Purge before start: enclosures and the gas side of process compressors are usually purged with nitrogen or air before starting.
- Start-up: confirm ventilation, detection and permissives before the driver starts.
- Normal running: monitor discharge temperature, vibration, seal leakage and gas detection.
- Upset: define actions for high temperature, high vibration, gas alarm and loss of cooling.
- Emergency shutdown: isolation, blowdown and how the machine is left safe.
- Maintenance: permit-to-work, gas-free testing and hot-work rules.
Sizing the package for the real duty
Hazardous-area equipment costs more and takes longer to source, so oversizing is costly. Size on the real demand profile: peak and minimum flow, pressure at the point of use (bar and psig), and how flow is controlled. For air duties, every extra bar of pressure costs about 7% more power, so state the minimum pressure the process actually needs. Consider whether a standby unit or a rental machine will cover maintenance periods.
How Reddy Compressors helps
We sell (new and used/refurbished), rent and service air and gas compressors, including CNG, nitrogen, process gas and booster machines, and supply spares across India. As an independent multi-brand specialist, we can ask several manufacturers for hazardous-area packages on the same, clearly written basis so that you can compare offers fairly. Our own rental fleet covers 50–2,000 cfm and 2–30 bar (29–435.1 psig), diesel and electric; where a hazardous-area site needs rental air, we discuss what spark arrestors, intake shut-off valves or safe-area placement the machine needs, and the final acceptance rests with your site safety team.
We work from Tarnaka, Secunderabad, with more than 20 service engineers and technicians covering Telangana and Andhra Pradesh. On hazardous-area sites we follow the plant’s permit-to-work system. We do not classify areas or issue Ex certificates; those remain with the plant’s competent person and the certified manufacturers. Oxygen, hydrogen and toxic-gas duties still follow the gas-specific codes and the compressor maker’s design rules.
What to send us
- Area classification drawing or a statement of zone, gas group and temperature class.
- Whether the compressor handles air or a flammable gas, with composition if gas.
- Flow, pressure (bar and psig) and the demand pattern.
- Location: indoor, outdoor, enclosure, and ambient temperature range.
- Power supply, preferred driver (electric or diesel) and whether a VFD is wanted.
- Your specification, any required approvals (PESO, IECEx, ATEX) and documentation needs.
Frequently asked questions
What information do I need to buy a compressor for a hazardous area?
You need the zone (0, 1 or 2 for gas; 20, 21 or 22 for dust), the gas group (IIA, IIB or IIC) and the temperature class (T1 to T6) from the plant’s area classification. Add the gas being compressed, flow, pressure, ambient conditions, driver type and the approvals your site requires. Without the classification, a supplier can only guess, and offers cannot be compared.
Can a standard air compressor be used in a Zone 2 area?
Not as standard. A Zone 2 package needs electrical equipment suitable for Zone 2, such as Ex ec motors, suitable instruments and enclosures, surface temperatures within the temperature class, and an intake that cannot draw in flammable vapour. Some manufacturers offer Zone 2 versions of their standard machines. The package must be assessed as a whole, not just the motor.
Who is responsible for hazardous area classification?
The plant owner or operator is responsible, normally through a competent engineer applying IEC 60079-10-1 for gases and IEC 60079-10-2 for dusts. The compressor supplier needs the classification result to select certified equipment but does not classify the plant. Changes to the plant, including adding a gas compressor, may require the classification to be reviewed.
Can a diesel compressor work in a hazardous area?
It can only work where the site’s safety team accepts it, usually with extra protection: a spark arrestor on the exhaust, exhaust and surface temperature control, an automatic air-intake shut-off valve to stop overspeed if flammable gas is drawn in, and suitable electrics. Often the safer answer is to place the diesel machine in a safe area and pipe the air in.
What does a marking like Ex db IIB T4 Gb mean?
Ex db means flameproof enclosure protection. IIB is the gas group, covering gases such as ethylene as well as the easier IIA gases. T4 means the maximum surface temperature is 135 °C. Gb is the equipment protection level suitable for Zone 1. Check that every marking on the package matches or exceeds the zone, gas group and temperature class of your area.
Does a VFD-driven motor need special approval for hazardous areas?
Yes. A motor’s hazardous-area certificate must cover operation with a variable-frequency drive, because inverter supply changes heating, bearing currents and voltage stress. The drive itself is usually placed in a safe area. Check the motor certificate, the speed range permitted and any thermal protection requirements before combining a certified motor with a VFD.
Related pages
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.