A1      There is a large database of dusts.

A2      The HSE document ‘ATEX, A Guide for Laboratories’ addresses this issue.

A3      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 maintain constantly an 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, to use containers that minimise the risk of spills during transfer, and in particular to 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.

A4      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, if the largest release foreseeable from a single failure is 25kg of dust, hazardous area classification is not normally appropriate.

A5      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, e.g. by corrosion, impact or vibration

There is ongoing work to assess the size of gas cloud in the explosive range expected to form from holes of specified sizes, and different mains gas supply pressures. 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.

A6      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 machines continue to operate after it becomes ineffective. It is also possible if dust deposits on horizontal surfaces within the building are disturbed, e.g. 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.

A7      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 the organisation. Some manufacturers run training courses for installation of their particular equipment. Those installing such equipment should at least understand hazardous area classification drawings, and the markings associated with ATEX equipment.

A8      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, leaked these gases, and a major fire has resulted. 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 a leak is most likely when individual cans can 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 has accepted 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.

A9     The application of ATEX to simple valves has been discussed by the EU members and the EU commission. The conclusions of these discussions, and similar application questions are on the EU commission website.

Despite this, some valve manufacturers may still be offering for sale products they claim are ‘ATEX compliant’ and carrying ATEX markings, even though the valves are out of scope.