Guidelines on Safety
(a) Only pressure vessels built to a National European, or International Standard, for example, EN286 Pt.1 or EN13445, should be used for Air Receivers.
(b) It is essential that a non-return valve and shut-off valve are fitted in the delivery line when the compressor is to be coupled in parallel with another compressor or connected to an existing air supply system; in such cases a pressure release valve must be provided upstream of the valve, unless one is already fitted on the compressor.
(c) Distribution pipes and hoses must be of the correct size and suitable for the expected maximum working pressure; the tightness of compression fittings must be checked regularly.
(d) Do not use frayed, damaged or deteriorated hoses; always store hoses properly and away from heat sources or direct sunlight; a hose failure can cause injury.
(e) Use only the correct type and size of hose end fittings and connections: Use clamps of robust construction especially made for compressed air.
(f) Use eye protection; if using compressed air for cleaning down equipment, do so with extreme caution; take care not to blow dirt at people or into machinery. (Blow guns also H & SE H(G) 39). With blowguns, unless of safety pattern, the pressure should not exceed 2 bar gauge.
(g) Never apply compressed air to the skin or direct it at a person; even air pressure of 1 bar can cause serious injury; never use a compressed air hose to clean dirt from clothing.
(h) When blowing through a hose or air line, ensure that the open end is held securely: a free end will whip and can cause injury; open the supply air cock carefully and ensure that any ejected particles will be restrained; a blocked hose can become a compressed air gun.
(i) Do not use air directly from a compressor for breathing purposes, for example charging air cylinders or supplying masks or hoods, unless the system has been specifically designed for such a purpose and breathing air filters and regulators are fitted. See BS4275 and BSEN12021
(j) Never operate any part of a compressed air system, be it compressor, pipes or pneumatic appliance, at a higher pressure than that for which it has been designed and rated. If any equipment has a design pressure less than the maximum output pressure of the compressor it shall be protected by suitable means against over Pressure.
(k) Shut off the adjacent upstream isolating valve and release the air pressure before disconnecting a hose or line, unless there is an automatic valve to give protection at the upstream joint being separated.
(l) Attention is drawn to the safety requirements specified in ISO 4414 and to the requirements of the EC Directive 89/392/EEC- relating to the "Safety of Machinery".
(m) A potential source of hazard is the mismatching of screw threads between the external thread of the pipe or connector and the internal thread of the socket or component. The possibility of mismatch is usually caused by the incorrect or insufficient descriptions in orders, catalogue sheets and installation instructions The most commonly used pipe threads are BS21 (ISO7-1), BS2779 (ISO228-1) and the American thread ANSI B1.20.1 (This standard contains 6 forms of pipe thread but NPT is the most common). Threads should always be described as specified in the appropriate standard in order to ensure correct matching. Careless use of terminology is certain to cause trouble. It is not uncommon to see a thread described as ½" BSP but such description is meaningless because:
- The inch sign should never be used (even the ANSI standard omits it).
- No information is given as to whether BS21 or B52779 is intended.
- No information is given as to whether taper or parallel threading is required.
- No information is given regarding internal or external threading.
It should be noted that threads to ISO7-1 (BS21) and ISO 228-1 (BS2779) should never be interconnected except that an external taper thread to ISO7-1 can be used with an internally threaded port to ISO 1719:1981 (BS5380:1984). These are threaded to ISO228-1 but have an additional internal run out to prevent the taper external connector bottoming before sealing is achieved. Attention is drawn to the publication 'Industrial Screw Threads'.
(n) It is often preferable to provide safety, operations and maintenance warnings on equipment by means of symbols rather than text. These are more easily read at a distance and avoid the need for translation into other languages, attention is drawn to BS7234 (ISO7000) and BS3641 which include symbols that are suitable for use with compressed air equipment.
During Operation
(a) Keep doors shut on silenced plant. On other plant, check whether it should be run with doors open or shut.
(b) Check all pressures and temperatures are correct; refer to the operating instructions.
(c) Stop the plant if warning lights show or if gauges register outside normal limits; untrained personnel must not attempt adjustments; call in a plant fitter to investigate.
(d) Do not make adjustments inside the canopy when a machine is running, unless appropriate precautions are taken.
(e) Do not remove guards.
(f) Do not use the machine in a fire hazard area unless it is suitably designed; do not operate in the vicinity of toxic fumes.
(g) Ensure that all pneumatic control equipment and air line accessories are always operated below their maximum rated pressure and temperature.
Maintenance Overhaul
(a) Ensure that all air pressure is completely released from the system and that it is isolated from other air systems. In multi-compressor installations repairs to any other compressors shall not be carried out whilst the other compressors are working, without first closing the isolation valve and venting and disconnecting the delivery pipe of the compressor to be repaired.
(b) Ensure that a machine cannot be started inadvertently; isolate the unit and lock the isolator in the safe position; place warning notices on isolator (Danger men at work).
(c) Ensure that any door that opens upwards is securely fastened when open; and that no door can slam shut.
(d) When working on the plant:
- Use proper lifting gear of adequate capacity.
- Examine condition of lifting tackle before lifting plant.
- Use correct tools for the job.
- When using a chemical or solvent cleaner, follow the manufacturers' instructions. Be sure any fluid used cannot cause any chemical reactions or explosion in combination with high pressure. Therefore do not use halogenated hydrocarbons in application equipment where aluminium or galvanized parts come in contact with solvent or coating material.
- Halogenated hydrocarbons e.g. 111-trichloroethane and methylene chloride react violently with such parts, causing corrosion and very high pressure increases if entrapped.
- Do not weld or perform any other operation involving heat near the electric or oil systems; oil and fuel tanks must be purged completely, for example, by steam cleaning, before any welding repairs are carried out.
- Do not weld or in any way modify any pressure vessel.
(e) Before clearing the machine for use:
- Check that the sump is filled with the correct grade of oil.
- Check direction of rotation
- On water-cooled units, check that the coolant is flowing.
- Check that operating pressure, temperatures and speed are correct and that the controls and shutdown devices work correctly.
(f) With lubricated reciprocating compressors; every six months examine the discharge pipe and discharge pulsation damper for carbon deposits, if excessive, the deposits should be removed.
(g) Isolating valves, which should be of the self-exhausting type should if possible, be of the type designed for locking in the 'off' position. When servicing pneumatically-operated machines, lock the isolating valves so that air pressure cannot be applied inadvertently while the machine is being worked on.
(h) Maintain filters in accordance with supplier's instructions as a reduction in air pressure caused by choked filter elements could cause malfunction of pneumatic equipment.
(i) Inspect hoses, flexible lines and plastic pressure containing components at regular intervals and replace it signs of cracking, grazing or any form of mechanical damage are evident.
(j) At each maintenance operation inspect the pressure containing envelope of all items for signs of corrosion or damage and if found, report your findings to a competent person. Regulation 12 of the Pressure Systems Regulations requires owners and users of compressed air systems to ensure that the whole system is properly maintained in good repair.
Overpressure protection
(a) If any equipment having a design pressure lower than the maximum output pressure of the compressor is used, or if an increase of pressure above normal operating pressure will cause a malfunction, it shall be protected against overpressure by suitable means.
(b) Any relief valve shall have a design flow capacity such as that when subjected to the maximum output pressure and flow of the compressor, and taking into account the flow restriction caused by the upstream pipes and fittings, it will prevent exceeding the design pressure of the equipment. This requirement may, in certain circumstances and depending upon compressor pressure and design pressure of the equipment, imply the need for a relief valve having a port size at least twice the nominal diameter of the pipe and pressure regulator feeding the equipment.
(c) An alternative method of protection is the use of a smaller relief valve in conjunction with an automatic isolating valve which shuts off the air supply to the equipment if the pressure rises more than 20% above the blow off pressure of the relief valve. If this method is used, it is essential to ensure that sudden cessation of air supply to the equipment cannot cause a hazard.
(d) Pressure gauges should be checked for accuracy at regular intervals. A pressure gauge which, for no obvious reason, starts to indicate pressures higher than normal should be checked for accuracy without delay. Pressure indications higher than normal, when there is no reason to believe that a pressure increase has occurred, may indicate the possibility of weakening and potential explosive failure of the Bourdon tube.
(e) Non reclosing pressure relief methods such as bursting disc or buckling pin devices should not be used as the sole method of pressure relief. A correctly sized pressure relief valve will maintain the system at or near normal working pressure allowing an orderly shut down to correct the fault. Non reclosing devices can result in complete loss of system pressure which may in itself be a hazard.
Hot air ducting
If it becomes necessary to breach a wall for the ductwork to carry the hot air to an adjoining factory area make certain that such action is not contrary to the requirements of the Factories Act, the Fire regulations or the rules of your own insurance company.
Circuit diagrams
Ensure that the installer of the compressed air system provides a full circuit diagram, using symbols from ISO 1219, showing the location and description of all protective devices and those items requiring regular maintenance. Nominate one of your employees to be responsible for ensuring that the diagram is updated whenever any additions or modifications are made to the system. These actions will not only ensure that you comply with the recommendations of the Health and Safety Executive as specified in Clause 73 of their publication "Compressed Air Safety" (HS (G)39) but will also assist the competent person, nominated to draw up or certify your Written Scheme of Examination, required by the Pressure System Safety Regulator, to provide this service at the lowest cost.
