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
- 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
- Incompetence of maintenance staff; and
- Poor communication between maintenance and production staff.
Contributory factors for an assessor to consider concerning maintenance
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
- 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
- Whether maintenance schedules are managed and regularly inspected and
- Whether Human factors (stress, fatigue, shift work, attitude) are
- 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 &
- 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
- 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
- Scheduled maintenance not being undertaken as required or breakdown
maintenance inadequate, leading to unrevealed failures of safety
- 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
- 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
Paragraph 52 refers to a routine checklist that should regularly be
applied to any electrical equipment used in potentially explosive
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
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