A marking such as II 1G Ex ia IIC T4 Ga on a gas detector's label tells you in which zone, with which gases and with what surface temperature limit the device may be used. This guide explains the Ex marking, the match between zone and category, sensor types and bump testing with diagrams.
After the hexagonal Ex symbol comes the ATEX part, then the protection data to IEC 60079. The marking below is an example.
- IIGroup II: surface industries, not mining
- 1Category 1: very high protection, zone 0 or 20
- GGas atmosphere (D = dust)
- Ex iaIntrinsic safety, highest level
- IICGas group IIC: hydrogen, acetylene
- T4Surface temperature at most 135 °C
- GaEquipment protection level: for zone 0
Mining uses Group I with categories M1 and M2. The device’s real marking is on its label and certificate.
| Zone (gas · dust) | Cat. 1 | Cat. 2 | Cat. 3 |
|---|---|---|---|
| 0 · 20: explosive atmosphere continuously or for long periods | Yes | No | No |
| 1 · 21: likely to occur occasionally in normal operation | Yes | Yes | No |
| 2 · 22: not expected normally, and only briefly if it occurs | Yes | Yes | Yes |
In Türkiye the 2014/34/EU equipment regulation (Official Gazette 30.06.2016, 29758) applies to equipment, and the regulation on protecting workers from explosive atmospheres (30.04.2013, 28633) to zoning at the workplace.
- Ex dFlameproof enclosure: an internal explosion does not escape (IEC 60079-1)
- Ex eIncreased safety: no sparks or hot spots (IEC 60079-7)
- Ex ia·ib·icIntrinsic safety: circuit energy too low to ignite; ia suits zone 0 (IEC 60079-11)
- Ex pPressurisation: the enclosure is kept full of protective gas (IEC 60079-2)
- Ex mEncapsulation: parts are embedded in compound (IEC 60079-18)
- Ex tDust protection by enclosure (IEC 60079-31)
The highest temperature the device surface may reach. The class chosen must stay below the ignition temperature of the gas present.
- IIAExample: propane
- IIBExample: ethylene
- IICExamples: hydrogen, acetylene
- IIIACombustible flyings
- IIIBNon-conductive dust
- IIICConductive dust
IIC equipment may also be used for IIB and IIA, not the other way round. For dust, IIIC likewise covers IIIB and IIIA.
- CATCatalytic bead: flammable gas as % LEL; needs at least 10% oxygen; silicones, lead and sulphur compounds poison it
- IRInfrared: hydrocarbons and CO₂; needs no oxygen and is not poisoned; cannot detect hydrogen
- ECElectrochemical: oxygen and toxic gases such as CO and H₂S
- PIDPhotoionisation: volatile organic compounds at ppm level
Two reference values are used for 100% LEL methane. Which one the detector is set to changes the reading.
The difference means up to 13.6% deviation in the reading. The calibration gas certificate and the detector setting must use the same reference.
- BUMPBump test: no adjustment; checks that sensors respond to test gas and alarms go off. Recommended daily before use
- CALCalibration: the reading is adjusted against gas of known concentration; the maker sets the interval
Every device used in an explosive atmosphere must be designed so that it cannot ignite that atmosphere, and must show this on its label. Portable and fixed gas detectors are no exception. The marking on the label has two parts: first the group and category under ATEX, then the protection method, gas group and temperature class under IEC 60079.
How to read the diagrams
- Ex marking: in the example, II stands for surface installations, 1G for the highest category in gas atmospheres, Ex ia for an intrinsically safe circuit, IIC for the most demanding gas group and T4 for a surface temperature limit of 135 °C.
- Zone and category: the zone describes how often an explosive atmosphere occurs at the workplace and comes from the employer's classification. In zone 0 or 20 only category 1 devices may be used; in zone 1 or 21, category 1 or 2 devices.
- Protection methods: the letters d, e, i, p, m and t show how ignition is prevented.
- Temperature class: from T1 to T6, the surface temperature limit falls. The temperature of the selected class must stay below the ignition temperature of the gas present.
- Gas groups: a device marked IIC can also be used in IIB and IIA atmospheres; the reverse does not apply.
- Sensors: a catalytic sensor needs at least 10% oxygen and can be poisoned by certain substances. An infrared sensor needs no oxygen but cannot measure hydrogen. Electrochemical sensors are used for oxygen and toxic gases, PID sensors for volatile organic compounds.
- Methane reference: two reference values are used for 100% LEL methane: 4.4% and 5.0%. If the device and the calibration gas are not set to the same reference, the reading will be off.
- Bump test and calibration: a bump test checks whether the sensor responds to gas and makes no adjustment. Calibration corrects the device's reading against a gas of known concentration.
Short selection checklist
- Get the zone classification of the work area from the workplace's explosion protection document.
- Check that the device category suits this zone and that its gas group and temperature class cover the gases present.
- Choose the sensor type according to the gases to be measured: if hydrogen may be present, do not rely on an infrared sensor alone; if oxygen can fall below 10%, remember that a catalytic sensor cannot measure correctly.
- Check which methane reference the device's LEL setting is based on, and the certificate of the calibration gas.
- Bump test the device every day before use; follow the manufacturer's instructions for the calibration interval.
This guide is for general information. For zone classification and device selection, your workplace's risk assessment, the device certificate and the instructions for use apply.
Frequently asked questions
Can a category 3 device be used in zone 1?
No. Zone 1 or 21 requires at least a category 2 device. A category 3 device is suitable only for zone 2 or 22, while a category 1 device can be used in all three zones.
What is the difference between catalytic and infrared LEL sensors?
A catalytic sensor detects most flammable gases, including hydrogen, but needs at least 10% oxygen and can be poisoned by silicones, lead or sulphur compounds. An infrared sensor needs no oxygen and is not poisoned, but cannot measure hydrogen.
Are a bump test and calibration the same thing?
No. A bump test uses a short exposure to gas to confirm that the sensor responds and the alarm sounds; it does not change the device's settings. Calibration adjusts the device's reading using a gas of known concentration. A device that fails the bump test must not be used until it has been calibrated.
Sources
- European Commission – Harmonised standards: equipment for explosive atmospheres (ATEX)
- Resmî Gazete – Muhtemel Patlayıcı Ortamda Kullanılan Teçhizat ve Koruyucu Sistemlerle İlgili Yönetmelik (2014/34/AB) (29758) · 2016-06-30
- Resmî Gazete – Çalışanların Patlayıcı Ortamların Tehlikelerinden Korunması Hakkında Yönetmelik (28633) · 2013-04-30
This article is compiled from these sources; for technical values and obligations, the current edition of the source applies.
