an extract from safetyline magazine (No. 19 August 1993)
Are you working with a bomb?Owners may avoid the possibility of compressed air receivers
becoming potential bombs by completing this questionnaire. A survey by the Construction and Engineering Branch of WorkSafe Western Australia,
found that owners of storage vessels associated with air compressors
had a lack of knowledge about the safe operation and maintenance
of air receivers and did not understand legislative requirements
for pressure plant. Prior to November 1990 compressed air receivers, among other items
of plant, were required to be inspected by officers of the department's
Construction and Engineering Branch. From November 1990, employers were made responsible for the maintenance
and inspection of compressed air receivers and other machinery
listed under schedule 4 Part (B) of the Occupational Safety and
Health Regulations 1988. Owners and managers who cannot answer the following questions
correctly may be unaware of the hazards associated with air receivers.
Incorrect setting of safety valves could cause air receivers to
over-pressurise, and rupture or explode. Ignition of carbonised
oil could also cause an explosion. Where there is any doubt over correct procedures or the safety
of compressed air receivers, contact the Construction and Engineering
Branch, WorkSafe Western Australia on (08) 9327 8777 or (08) 9327
8707.
Air receivers quizQuestions - What do you understand by the following:
(a) Design pressure?
(b) Authorised working pressure?
(c) Working pressure? - What is the relationship between design pressure, authorised
working pressure and working pressure?
- What is the maximum pressure at which a safety valve can be
set to lift?
- What do you understand by the term accumulated pressure as
applied to a safety valve?
- What is the maximum permissible accumulated pressure on air
receivers?
- If you have two or more air receivers working in parallel,
how would you determine the authorised working pressure?
- What is the hazardous situation that could exist with lubricating
oil being carried over from the air receiver, particularly if
the oil used is not the oil recommended by the manufacturer of
the air compressor?
- Are the pressure gauges on your air receiver checked for accuracy,
and if so, what period of time exists between the checks?
Answers - (a)The maximum pressure at which the air receiver
is designed to operate. This pressure has been determined by
calculations and proved by various tests.
(b) The maximum pressure at which the inspecting authority
will permit the air receiver to operate.
(c)The pressure the owner/manager decides the air receiver
will operate at, usually in the order of 10 per cent below the
authorised working pressure so that the safety valves are not
lifting all the time. - The authorised working pressure can be the same as the design
pressure or less but can not be greater than the design pressure.
The working pressure can be the same as the authorised working
pressure but for practical purposes it is usually 10 per cent
less.
- The maximum set pressure of a safety valve can be no greater
than the authorised pressure.
- The accumulation is the pressure increase that may occur after
the safety valve starts lifting.
- Ten per cent above lift pressure.
- The authorised working pressure is established by adopting
the lowest design pressure or as per Reg. 504 of the Occupational
Safety and Health Regulations.
- Under certain conditions of operation (e.g. leaking discharge
valves), oil carried over into the air receiver could carbonise
with the inherent risk of an explosion.
- Pressure gauges should be checked at least every 12 months,
and certainly prior to setting or checking the lift pressure of
a safety valve.
Copies of this publication may be freely printed and distributed provided that WorkSafe Western Australia
receives appropriate acknowledgement, and that no substantial changes are made to the text.| [WorkSafe Western Australia] | Sla-93-(96) |
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