Permit to Work Systems
This Technical Measure Document refers to permit to work systems required
to control work such as maintenance activities on chemical plant and so
prevent a major accident.
See also Technical Measure Documents on:
The relevant Level 2 Criteria are 18.104.22.168(91)
The following aspects should be considered with respect to Permit to Work
- Human factors;
- Management of the work permit systems;
- Poorly skilled work force;
- Unconscious and conscious incompetence;
- Objectives of the work permit system;
- Types of work permits required; and
- Contents of the work permits.
The following issues may contribute towards a major accident or hazard:
- Failing of the site safety management system;
- Failure to recognise a hazard before and during maintenance;
- Failure to comply with the work permit system in hazardous
- Communication failure during the use of a work permit system.
Contributory factors for an assessor to consider concerning the Work
The Safety Report should address the following points:
- Whether staff have been sufficiently informed, instructed, trained and
supervised to minimise a potential human failing during operation of the
work permit system;
- Whether the work permit system includes sufficient safety information,
maintenance instructions, correct PPE and equipment for use;
- Whether the work permit contains sufficient information about the type
of work required (Equipment removal, excavation, hot/cold work,
repairing seals, vessel entry, waste disposal, isolation);
- Whether there is sufficient provision available to fulfil the
requirements of the work permit system;
- Whether the employees responsible for control of the maintenance work
are identified within the work permit system and that the work is
properly authorised by a responsible person;
- Whether the work permit system is managed, regularly inspected and
- Whether all work permits are kept on file;
- Human factors (stress, fatigue, shift work, attitude);
- Whether sufficient precautions are taken prior to initiating a work
permit (isolation, draining, flushing, environmental monitoring, risk
assessments, communication, time allotted for the work);
- Whether staff are aware of the type of environment they are working in
during the operation of a work permit (flammable, corrosive, explosive,
zones 0, 1 & 2, electricity supplies);
- Whether the person responsible for operating the plant is aware of the
type of maintenance involved and how long it is likely to take; and
- Whether the work permit system involves a formal procedure whereby the
maintained plant or equipment is handed back to operation.
Major hazards could arise from the following:
- Wrong type of work permit used;
- Wrong information about work required on the work permit;
- Failure to recognise the hazards where work is carried out (e.g.
- Introduction of ignition source in controlled flameproof area (e.g.
welding, non spark-proof tools, non-intrinsically safe equipment used in
intrinsically safe zones);
- Terms of work permit not adhered to (e.g. failure to isolate plant
and/or drain lines of hazardous substances);
- Failure to hand-over plant in safe condition on completion of
work/cancelling of work permit;
- Unauthorised staff performing work permit functions;
- Poor management of the work permit system; and
- Insufficient monitoring of the work permit system.
Guidance relating to permit to Work Systems
The following HSE publications can be used as guidance material relating
to safety issues surrounding permit to work systems:
HS(G)5 Hot work : welding and cutting on
plant containing flammable materials, HSE (Not in current HSE list).
Paragraph 3 refers to the precautionary measures needed when welding in
areas that could be potentially flammable by planning and controlling the
task using a work permit system.
Paragraph 72 refers to the importance of management controlling the work
Paragraph 73 refers to the principles that should be followed when operating
a work permit system.
HS(G)48 Reducing error and influencing
behaviour, HSE, 1989.
Paragraph 27 refers to conscious incompetence whereby an employee
consciously refused to follow the work permit system to help an operator. A
breathing line was not assessed and an operator inhaled nitrogen instead of
air. Had the work permit system been managed properly then the event would
not have occurred.
HS(G)51 Storage of flammable liquids in
containers, HSE, 1998.
Paragraph 48 illustrates a permit to work system and summarises its expected
HS(G)64 Assessment of fire hazards from
solid materials and the precautions required for their safe storage and use,
Paragraph 28 refers to the need for a work permit system if a source of
ignition is introduced such as welding, cutting or grinding. The system
should contain any fire precautions necessary.
HS(G)65 Successful health & safety
management, HSE, 1997.
The section called; `Devising Risk Control Systems RCSs' under Inset 11,
illustrates the permit to work system as an example of a management control
loop i.e. plan, do, check and act. It demonstrates how risks in the work
place can be reduced if they are controlled and managed.
HS(G)77 COSHH and peripatetic workers, HSE, 1992
Paragraph 19 refers to the inclusion of a work permit system in a COSHH
assessment. It highlights the importance of safeguarding against risk when
carrying out work on a chemical plant.
Further reading material
The following publications are useful references relating to aspects of
permit to work systems:
OIAC. Guidance on
permit-to-work systems in the petroleum industry, Oil Industry
Advisory Committee, HSC, 1997.
IND(G) 98 (Rev 3) Permit-to-work systems, Free
copy available at HSE Books online ISBN 0 7176 1331 3, HSE, 1997.
Guidance on permit-to-work systems in the petroleum industry. ISBN 0 7176
1281 3, HSE, 1997
Loss Prevention in the Process Industries: Hazard Identification,
Assessment and Control. Frank P Lees 1996, 2nd Edition, vol 2 ch. 20 and 21.
ISBN 0 7506 1547 8. Published by Butterworth Heinemann.
Case studies illustrating the importance of permit to Work Systems
Hickson and Welch Ltd Fire (22/9/1992)
Pasadena - Phillips 66 (23/10/1989)
San Francisco Natural Gas Pipeline