This Technical Measures Document refers to the maintenance procedures that are necessary to mitigate a major accident or hazard.
See also Technical Measures Documents on:
The relevant Level 2 Criteria are:
The following aspects should be considered with respect to Maintenance Procedures:
- Human factors;
- Poorly skilled work force;
- Unconscious and conscious incompetence;
- Good maintainability principles;
- Knowledge of failure rate and maintainability; and
- Clear criteria for recognition of faults and marginal performance.
The following issues may contribute towards a major accident or hazard:
- Failure of safety critical equipment due to lack of maintenance;
- Human error during maintenance;
- Static or spark discharge during maintenance in an intrinsically safe zone;
- Incompetence of maintenance staff; and
- Poor communication between maintenance and production staff.
Contributory factors for an assessor to consider concerning maintenance procedures
The Safety Report should address the following points:
- Whether the company maintenance regimes (planned, risk-based, reliability centred, condition based or breakdown maintenance) are adequate for each plant item which has a safety function;
- Whether proof check periods quoted for safety critical items are adequate to ensure risks are within acceptable limits;
- Whether the procedures to ensure quoted proof check periods for safety critical items are adhered to;
- Whether the company Safety Management System includes adequate consideration of maintenance of plant, instrumentation and electrical systems;
- Whether maintenance staff have been sufficiently trained to recognise plant or equipment failing during maintenance inspections;
- Whether maintenance staff have been sufficiently informed, instructed, trained and supervised to minimise a potential human failing during maintenance;
- Whether maintenance schedules are managed and regularly inspected and reviewed;
- Whether Human factors (stress, fatigue, shift work, attitude) are addressed;
- Whether sufficient precautions are taken prior to maintenance of hazardous plant and equipment (isolation, draining, flushing, environmental monitoring, risk assessments, permits to work, communication, time allotted for the work);
- Whether the maintenance staff are aware of the type of environment they are working in (flammable, corrosive, explosive, zones 0, 1 & 2);
- Whether the maintenance staff use the correct equipment in the workplace during re-conditioning, replacement and re-commissioning (static free, intrinsically safe, flameproof, PPE/RPE);
- Whether sufficient maintenance systems are in place during productive assistance , servicing, running of plant, plant shutdown and plant breakdown;
- Whether procedures are in place to provide detailed operating instructions for re-commission plant after maintenance, which have been subjected to risk assessments (see Technical Measures Document on Plant Modification / Change Procedures);
- Whether sufficient reporting systems are in place so that corrective maintenance can be applied to mitigate a major accident or hazard.
Major hazards could arise from the following:
- The lack of control of spares such that incorrect materials or items outside specification (e.g. non-flameproof equipment) are used in replacement of plant items leading to increased risk of loss of containment, fire or explosion;
- Failure to drain and/or isolate plant prior to dismantling causing release of flammable or toxic substances;
- Maintenance being performed incompetently (particularly alarm/action set points on instruments incorrectly set, alignment of couplings on pumps and agitators causing overheating, motors running in wrong direction, safety features left disconnected/dismantled, gaskets left out, bolts torqued incorrectly or bolts missing, non-return valves orientation incorrect, pipework/flexibles incorrectly connected/installed, pipeline spades/orifice plates left in/removed, relief valve springs overtightened, bursting discs orientation incorrect/left out);
- Scheduled maintenance not being undertaken as required or breakdown maintenance inadequate, leading to unrevealed failures of safety critical items;
- Lack of knowledge by maintenance staff of the working environment where maintenance is being carried out (i.e. lack of risk assessments, warning signs, method statements, emergency procedures), leading to ignition of flammable substances (e.g. heat sources such as cigarettes or welding, static and electrical discharge, use of non spark-resistant tools) or injury/fatality from incorrect personal protective equipment (e.g. respirators) being worn;
- Unauthorised staff performing maintenance functions; and
- Failure to re-commission plant correctly after maintenance to ensure that operations are not adversely affected in terms of safety considerations (e.g. contamination, flow rate changes, heat transfer rate changes, mass transfer rate changes).
Guidance and Codes of Practice relating to maintenance procedures
The following publications can be used as guidance material relating to maintenance procedures:
- HS(G)22 Electrical apparatus for use in
potentially explosive atmospheres, HSE, Not in current HSE list.
Paragraph 49 refers to the importance of good engineering practice and a knowledge of the maintenance history for any electrical apparatus with explosive protection capabilities.
Paragraph 51 refers to BS 5345 (Code of Practice for the selection, installation and maintenance of electrical apparatus for use in potentially explosive atmospheres (in 8 parts)) which lists the typical maintenance schedules for each type of electrical apparatus.
Paragraph 52 refers to a routine checklist that should regularly be applied to any electrical equipment used in potentially explosive atmospheres.
Paragraph 55 refers to the need to recognise the correct explosive markings on a piece of electrical equipment so that the correct type of maintenance can be applied.
- HS(G)51 Storage of flammable liquids in
containers, HSE, 1998.
Paragraph 48 refers to the need to implement a permit to work in areas where flammable liquids are stored.
- HS(G)71 Chemical warehousing: the storage of
packaged dangerous substances, HSE, 1998.
Paragraph 54 refers to the importance of contractor competence to mitigate hazards that may be created during maintenance and repair.
- HS(G)140 Safe use and handling of flammable
liquids, HSE, 1996.
Paragraph 48 refers to the need for maintenance to prevent electrostatic build up within flammable environments by regularly checking the earth continuity of all metal services in contact with flammable atmospheres (see BS 7430 : 1998 Code of practice for earthing).
Paragraph 52 refers to the need to not place too much reliance on the use of spark-resistant tools in flammable areas but to remove all flammable materials before work is done, if practicable, and the need to keep such tools free of imbedded particles.
Paragraphs 70 – 72 refers to the precautionary steps needed prior to carrying out maintenance including risk assessing the environment and using a work permit system.
- HS(G)176 The storage of flammable liquids in
tanks, HSE, 1998.
Paragraphs 104 refers to pumps being potential ignition sources and that they should be located outside a bunded area, on an impervious base, in the open air. This will avoid damage from fires or spillages in the bund and facilitate access for maintenance.
- LPGA Code of Practice 1. Bulk LPG Storage at Fixed Installations (Part
1, Part 2, Part 3 and Part 4), LP Gas Association.
Supersedes HS(G)34 Storage of LPG at fixed installations, HSE, 1987.
Part 3 gives full details of maintenance requirements.
Further reading material
- HSE, 'Dangerous Maintenance - A Study of Maintenance Accidents and how to prevent them', HSE Books, ISBN 0 11 886347 9, 1992.
- Male, G.E., 'Safety of Transport and Machinery. A Survey of
Maintenance Accidents Attributed to Technological Failings', HSE
Specialist Inspector Report SIR52, 1998.
Explains the different types of maintenance regimes and gives data on accidents that have occurred.
- Czachur, K.J., Bright, C.K. and Beic-Kharasani, R., 'Condition Monitoring to Enhance Safety', HSE Contract Research Report No. 120/1997. ISBN 0 7176 1254 6.
Case studies illustrating the importance of maintenance procedures
- Associated Octel Company Limited (1/2/1994)
- Bhopal - Union Carbide (3/12/1984)
- BP Oil (Grangemouth) Refinery Ltd (13/3/1987)
- BP Oil (Grangemouth) Refinery Ltd (22/3/1987)
- BP Oil - Dalmeny Refinery (11/6/1987)
- Flixborough (Nypro UK) Explosion (1/6/1974)
- Hickson and Welch Ltd Fire (22/9/1992)
- Pasadena - Phillips 66 (23/10/1989)
- San Francisco Natural Gas Pipeline Puncture (25/8/1981)
- Texaco Refinery - Milford Haven - Explosion and Fires (24/7/1994)
- COMAH: Notification form
- A guide to the COMAH regulations 2015 (L111)
- Leadership for the major hazard industries
- Better alarm handling