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 5.2.4.1(91) and 5.2.4.2(95).

General principles

The following aspects should be considered with respect to Permit to Work Systems:

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 environments; and
Communication failure during the use of a work permit system.

Contributory factors for an assessor to consider concerning the Work Permit System

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 reviewed;
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

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. flammable substances);
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 permit system.
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 contents.

HS(G)64 Assessment of fire hazards from solid materials and the precautions required for their safe storage and use, HSE, 1991.
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.

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 Puncture (25/8/1981)