General issues and information

Where can I find a list of dusts which are explosive?

To check if a dust is explosive, see: Database of combustion and explosion characteristics of dusts.

How do I zone my laboratory?

We have many products that are flammable but all are in small volumes. Further, none of the laboratory equipment is available in an ATEX form.

For guidance on this issue, see: Hazardous area classification and laboratory operations, which gives guidance on ATEX issues in laboratories.

We inspect service industry sites (eg nail technicians) which handle flammable solvents like acetone. What do we need to know about the amounts in the customer area, the precautions against spillage and zoning?

Highly flammable solvents, such as acetone, release vapours which are easily ignited. Where possible, less flammable solvents should be used in preference. Where highly flammable solvents are used and the public are present, it is difficult to constantly maintain effective control over all sources of ignition, such as smoking or portable electronic equipment. Consequently hazardous area classification is not appropriate. Instead, it is better to limit the amounts present, use containers that minimise the risk of spills during transfer and, in particular, avoid containers that will break if knocked over. The quantity held in the workroom should be limited to the amount used in half a day's work.

We inspect supermarkets with in-store bakeries. Some of these handle 25 kg sacks of flour, though others only have smaller quantities. They all have substantial stocks of sugar, custard powder and other products listed as explosible in the store and warehouse areas. Do I need to ask them to consider area classification?

Many food-type products comprise dusts that, if tested, are explosive. However, in shops or warehouse areas, there is usually no means to generate a large dust cloud, except very briefly if a bag or sack fails. If a sack tears during handling, usually only a small proportion of escaping dust will be raised into a cloud. Unless there is some way that more dust will be kept as a cloud for a longer period and – if the largest release foreseeable from a single failure is 25 kg of dust – hazardous area classification is not normally appropriate.

My steam boiler used for space heating and process steam runs on gas. It draws air from the room it is situated in, which is well ventilated. The room also contains the gas meter and 75 mm diameter pipework, running at 80 mbar with screwed joints. Do I need to zone the room? Does the burner control package mounted on the boiler need to comply with ATEX?

Low pressure pipelines carrying mains gas to gas burning equipment have not traditionally been considered as sources of hazardous leaks, and area classification has not been applied in such circumstances. Boiler houses are normally well ventilated, but the ventilation has usually been designed to provide air for combustion and to control room temperatures, rather than help disperse small leaks. The security of gas pipework operating at any pressure should at least be considered in any risk assessment made under DSEAR. Pipework is most likely to be reliably gas tight if:

  • it has been installed to a recognised relevant code
  • it has been properly maintained, including periodic pressure testing or leakage testing from the joints, and
  • there are no external influences likely to cause early failure, eg by corrosion, impact or vibration

There is ongoing work to assess the size of any potentially explosive gas cloud which may be expected to form, arising from the combination of the range of mains gas pressures and holes of specified sizes in such pipework. This is likely to be published by the Institution of Gas Engineers and Managers in due course.
Burner control packages mounted on the face of a boiler are often very close to hot surfaces, or air intakes that are directly connected to the internal flames. In these circumstances, it makes little sense to assign a hazardous area around the gas fittings or use ATEX-compliant electrical parts so close to other permanent sources of ignition. It is appropriate to design the pipework and gas control train to minimise the risk of a leak.

The vacuum cleaner salesman wants to sell me an ATEX vacuum cleaner for my woodworking machine shop. The machine shop has a small sanding machine, two spindle moulders and a planer / thicknesser, all connected to a central filter system. Can I buy the cheaper non-ATEX type?

Wood dust can explode if dispersed as a cloud and there may be a need to assign hazardous areas in a workroom like this, if dense dust clouds can form in the case of some equipment fault or operator error. This is possible if the local exhaust ventilation fails, or the machine continues to operate after if it becomes ineffective. It is also possible if dust deposits on horizontal surfaces within the building are disturbed, eg by a sudden air movement. In many cases, there is a need to assign zone 22 areas but only very limited need for any zone 21. Where this is the case, a vacuum cleaner built to ATEX category 3D should be selected. If there are any zone 21 areas, the machine or activity that generates the dust cloud should be stopped before any attempt is made to clean up deposits.

I have trained my electricians under the CompEx scheme to install ATEX equipment. Is there anything comparable for installation of non-electrical equipment? Do I need to train them specially?

There is at present nothing comparable to CompEx for the installation of non-electrical ATEX equipment, but there are tentative proposals to set up a competence scheme for people working at different levels in organisations. Some manufacturers run training courses for the installation of their particular equipment. Those installing such equipment should at least understand hazardous area classification drawings and the markings associated with ATEX equipment.

I operate a warehouse containing mixed toiletry products for retail sale, including aerosols containing flammable gas as the propellant. Do I need to zone the warehouse?

Most aerosols use liquefied flammable gases as the propellant, and many also contain flammable liquids as part of the product. You should ask your suppliers for details of the amounts and types of flammable liquids and gases in the products you store.

There are examples where aerosols have been damaged during mechanical handling operations and leaked these gases, resulting in a major fire. Such fires, in a pallet of aerosols, can develop very rapidly. There are advantages in separating aerosols from other less hazardous products in a fire-separated compartment of the warehouse.

Damage to aerosols leading to leaks is most likely when individual cans come loose from a larger package and fall to the floor. The chance of finding a can with a leak increases with old stock or where each individual can is not tested by the filler.

This issue has been discussed with the British Aerosol Manufacturers Association and they have published a guide to safe storage. Provided the conditions set out are very closely followed, HSE accepts that it is not essential to designate an aerosol warehouse as zone 2, and so ATEX-compliant vehicles are not needed. Where these conditions cannot be complied with, the warehouse should normally be classed as hazardous, zone 2.

I wish to purchase some new hand-operated valves for my chemical plant. I am confused to find that some manufacturers tell me they can supply valves bearing the Ex in a hexagon mark, while others claim this is not necessary. Do I need to specify ATEX compliance in my buying specification?

The application of ATEX to simple valves has been discussed by the EU member states and the EU Commission. The conclusions from these discussions, and similar application questions, are available on the EU Commission website .

Despite this, some valve manufacturers may still be marketing products they claim are 'ATEX-compliant' and carrying ATEX markings, even though the valves are out of scope of the Regulations. See EU Commission guidelines section 5.2.1 on Simple products.

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Updated 2023-01-09