Leak / gas detection

This Technical Measures Document refers to issues surrounding the detection of leaks and gases and what type of containment control systems have been designed to manage unplanned releases.

See also Technical Measures Documents on:

The relevant Level 2 Criterion is:

General principles

The following aspects should be considered with respect to Leak/Gas Detection:

  • Human Factors;
  • Objectives of leak/gas detection systems;
  • Types of leak/gas detectors required;
  • Maintenance of leak/gas detectors; and
  • Management of leak/gas detector systems.

The following issues may contribute towards a major accident or hazard:

  • Unrecognised high-risk areas, where detectors could be used;
  • No detectors or the wrong types in place in high risk areas;
  • Detectors incorrectly positioned and installed on site;
  • Poor level of maintenance and control of detection systems;
  • Too heavy a reliance on ineffective detectors.

Contributory factors for an assessor to consider concerning leak/gas detection

The Safety Report should address the following points:

  • The appropriateness of the types of detectors being used (UV detectors, IR detectors, smoke detectors, intrinsically safe detectors, heat detectors, specific substance detectors, explosimeters) in terms of the environment in which they are located and to perform the duty expected;
  • The effectiveness of using the detectors in terms of their positioning relative to the possible leak sources, taking account of dispersion and dilution of the released gases/vapours;
  • The effectiveness of the detectors for the types of substances to be detected (flammable substances, acid gases, smoke, explosive substances, toxic substances) at the concentrations required. Detectors may be chosen to react to more than one substance;
  • The types of protective devices linked to the detection systems (alarms, warning lights, reaction quenching systems, isolation systems, fire retardant systems, plant shutdown systems, trip devices, emergency services);
  • The reliability of each detector (range of detection, response time of detection, level of maintenance, calibration frequency, performance testing frequency, proof testing);
  • The detectors can be clearly seen, heard and understood, (appropriate warning signs, lighting, noise recognition), on plant, in the control room and off-site (if appropriate);
  • The procedures to respond to alarms, as a result of a leak/gas being detected (emergency evacuation plans, fire drills, risk assessing existing emergency evacuation plans), to confirm that the release has actually occurred and to record and investigate false alarms and take action to change the system to maintain the confidence of operators;
  • The level of risk associated with each potential leak source (risk assessments, risk-rating systems) and the reduction in that assessed risk value achieved by the use of detectors;
  • The provision and accessibility (to operators, maintenance staff etc)of a sufficient site plan which maps all potentially hazardous areas (zones 0, 1 & 2, segregation of compatible hazardous substances);
  • The detectors conform to British Standards such as BASEEFA (British Approved Service of Electrical Equipment in Flammable Atmospheres), if required.

Contributory factors for an assessor to consider concerning fire detection and control

The Safety Report should address the following points:

  • The types of fire detector systems in place (infrared detectors, ultraviolet light detectors, temperature detectors, smoke detectors);
  • The area covered by the detection system;
  • The reliability of the fire detection systems (fail-to-danger faults, spurious alarms); and
  • The types of fire protection systems in place (fire proofing, water sprays, foam/filming agents, monitor guns, combustible gas monitors, foam on tanks, fire walls/barrier walls, emergency relief venting for buildings, dust explosion control).

Major hazards

The Safety Report should address the following points:

  • Detector fails to detect in time (ie response time of instrument and/or response to high reading/alarm failing to prevent a major accident),
  • Detector fails in undetected unsafe state (reading zero),
  • Alarms, warning devices and protective devices fail to operate on demand,
  • A leak occurs which cannot be detected (due to position of sensor or weather conditions), and
  • Maintenance procedures not followed, increasing unavailability of system or rendering system ineffective.

Guidance and Codes of Practice relating to leak/gas detection

The following publications can be used as guidance material relating to safety issues surrounding the use of gas/leak detectors:

  • HS(G)22 Electrical apparatus for use in potentially explosive atmospheres, HSE, Not in current HSE list.
    Paragraph 6 – 18 refers to 8 types of protection against ignition in a potentially flammable atmosphere.
    Paragraph 20 refers to flameproof equipment having to meet BS 5501 : Part 5 : 1977. Also, all electrical apparatus must be approved by BASEEFA if used in flammable environments.
    Paragraph 51 refers to maintenance schedules listed in BS 5345.
    Paragraph 58 refers to the relevant legislation applicable to electrical apparatus in explosive atmospheres.
  • LPGA COP 1 Bulk LPG storage at fixed installations. Part 1 : Design, installation and operation of vessels located above ground, LP Gas Association, 1998.
    Supersedes HS(G)34 Storage of LPG at fixed installations, HSE, 1987.
    Part 1, Appendix A.1 recommends the use of suitably calibrated explosimeters to test for leak detection.
  • HS(G)34 Storage of LPG at fixed installations, HSE, 1987.
    Paragraph 21 refers to containment pits where it recommends that gas detectors be installed in case of leaks.
  • HS(G)176 The storage of flammable liquids in tanks, HSE, 1998.
    Paragraph 35 refers to electrical apparatus used in explosive atmospheres and refers to BS EN 60079-10.
  • HS(G)113 Lift trucks in potentially flammable atmospheres, HSE, 1996.
    Paragraph 43 refers to the use of intrinsically safe gas detection systems which will automatically shut down a truck in the event of a spillage or release of flammable vapour in a zone 2.
    Paragraph 46 refers to gas detectors being constructed to a zone 1 standard and set to operate at 25% of the lower explosive limit of a gas or vapour.
  • CS1 Industrial use of flammable gas detectors. Not in current HSE list.
    This document highlights the accuracy, instrument errors and the safety precautions required for the use of flammable gas detectors.

Further reading material

  • Control of Major Hazards – (3rd Report): Appendix 6 Heavy Gas Dispersion. ISBN: 0115537532.
    Appendix 6 refers to the use of gas detectors to generate hazardous substances dispersion profile data.

Case studies illustrating the importance of leak / gas detection

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