Advice on requirements for notifying and reporting gas incidents under the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 2013 (RIDDOR) and the Gas Safety (Management) Regulations 1996 (GSMR) (as amended)


Gas safety incidents have a high public profile and it is important that they are reported and investigated properly. The requirements of RIDDOR and GSMR aim to ensure that this happens in practice, however they do overlap and this can cause confusion. This document gives practical advice to help dutyholders (principally gas conveyors) to understand and comply with the relevant requirements of both RIDDOR and GSMR.

As well as their duties to notify, report and investigate incidents, gas conveyors have an overriding duty to make the situation safe at the scene of a gas incident.

RIDDOR requirements explained

RIDDOR Regulation 3 - The 'Responsible Person'

All RIDDOR reports should be made by the 'responsible person' as defined by RIDDOR Regulation 3.  For the majority of dangerous occurrences (DOs) arising from pipelines or pipeline works (RIDDOR Schedule 2, Part 1, paragraph 21 (a & b) refers), the responsible person is the pipeline operator - in most cases this will be the gas conveyor.  

For DOs involving failure of equipment involved with pipeline works (paragraph 21(c)) or escape of flammable substances (paragraph 26), the responsible person is the person in control of the premises where the DO occurred. 

A gas main or service is unlikely to be 'premises', therefore most reports of gas escapes should be made by pipeline operators under paragraph 21(a) rather than paragraph 26.   

The Health and Safety at Work etc Act 1974 (Application Outside Great Britain) Order 2013 defines both 'pipeline' and 'pipeline works'.  These definitions apply to both onshore and offshore pipelines.

RIDDOR Regulation 7 - Dangerous Occurrences

Regulation 7 requires that those DOs listed in Schedule 2, Part 1 of RIDDOR are reported.  Some DOs relating to gas escapes, fires and explosions may also need to be notified and investigated under GSMR.  These include:

  • Paragraph 21(a) - any damage to, accidental or uncontrolled release from or inrush of anything into a pipeline which could cause personal injury to any person, or which results in the pipeline being shut down for more than 24 hours; and
  • Paragraph 26 - the sudden, unintentional and uncontrolled release of gas inside a building (10 kg or more) or in the open air (500 kg or more).

The threshold criteria for uncontrolled releases under paragraph 26 (10 kg inside a building and 500 kg in the open air) are a useful starting point for deciding whether an escape 'could cause personal injury to any person'.  However a smaller gas escape may also meet this definition and should be reported under paragraph 21. 

Further advice on assessing whether gas releases from damaged mains and services should be reported ia available below.

RIDDOR Regulation 2 - Definition of a Dangerous Occurrence

To be reportable under RIDDOR, a DO must be work-related.  Downstream gas incidents caused by vandalism, attempted suicide, theft or other unauthorised interference by a member of the public are not RIDDOR reportable unless they result in death or major injury.  However, incidents of this nature may still need to be reported and investigated under GSMR - advice on GSMR requirements for reporting and investigating gas incidents is available below.

RIDDOR Regulation 11(1) – Death or Injury

Gas conveyors are required to report the death, loss of consciousness or hospital admission of a person arising in connection with an escape of gas conveyed by them.  The exception to this is where an employee of another undertaking is seriously injured or killed at work because of the gas escape.  In this case, their employer is the responsible person who should submit a RIDDOR report under Regulation 3(1) and the gas conveyor should not submit a duplicate report under Regulation 11(1).

GSMR requirements explained

GSMR Regulation 7(12) - escapes from domestic gas fittings

This applies to gas escapes at domestic premises resulting in a fire or explosion.  The gas conveyor immediately upstream of the emergency control valve (ECV) should investigate and establish whether the escape arose from installation pipework or from an appliance.

GSMR Regulation 7(13) - upstream gas escapes

Where there has been an escape of gas from the gas conveyor's part of the network (ie upstream of the consumer's ECV) which has, or was likely to have, resulted in a fire or explosion, the gas conveyor is required to carry out an investigation.  This should establish the source of the escape and the reason for it.  

GSMR Regulation 7(15) - carbon monoxide incidents

Gas conveyors making reports under RIDDOR Regulation 6(1) of incidents involving exposure to carbon monoxide from poorly installed or maintained gas appliances are required to inform the relevant gas supplier.  Gas suppliers have a duty to notify HSE and investigate such incidents (Regulations 7(14) and 7(16) of GSMR refer).

GSMR Regulation 7(16) - notification and investigation

This details the arrangements that gas conveyors need to have in place for carrying out investigations required by Regulations 7(12) and 7(13). These arrangements must ensure that the following duties are met.

  • HSE must be notified before the start of any investigation required by GSMR. This is to preserve evidence in the event of a separate HSE investigation. NB: Submitting a RIDDOR report does not meet the requirement to notify under GSMR. The requirements and routes for reporting under GSMR and RIDDOR are entirely separate.
  • whoever carries out investigations on behalf of conveyors must be competent to do so.
  • the conveyor must submit a report of their investigation to HSE whether or not there is a separate HSE investigation
  • the investigation must be conducted and the completed report sent to HSE as soon as is reasonably practicable to do so

In the event of an HSE investigation, management of the conveyor investigation and the submission of the investigation report to HSE should be discussed and agreed with the investigating inspector. This will ensure that the preservation of evidence is not compromised.

Guidance on preparing investigation reports is available below.

How to write GSMR investigation reports

This section is in two parts:

  • Part 1 - management issues relevant to investigations;
  • Part 2 - suggested report headings/contents.

It does not cover technical aspects of site investigation or investigations into incidents of carbon monoxide poisoning. Further information on downstream domestic gas incidents including carbon monoxide incidents is given in HSE operational guidance 'Domestic gas incidents investigation'.

Part 1 - Management arrangements for investigations

As well as being a legal requirement, GSMR investigations can enable dutyholders to check their performance and learn lessons to improve their health and safety management system. The gas conveyor's GSMR safety case should describe their arrangements for incident investigation, for example:

  • Policy and arrangements - conveyors should have a clear policy, organisation and arrangements for incident investigations. This should show how they meet their safety case commitment to investigate incidents and accidents (see paragraph 58 of HSE publication L80). The policy and arrangements should be integrated into their wider health and safety management system.
  • Aims and objectives - the investigation should be systematic with clear objectives that are understood by all involved. It should establish both immediate and underlying cause(s) and its conclusions should be consistent with the evidence. The likelihood of recurrence and possible consequences should be considered and any emerging trends identified. Wherever possible suitable steps to address the root causes and prevent recurrence should be identified and reflected in recommendations for further action.
  • Incident classification and allocation of resources - a system to categorise incidents based on potential, as well as actual, consequences should be used to ensure that the scale and depth of the investigation is proportionate to the incident.  It may be sufficient for supervisors to investigate minor incidents with limited potential consequences.  On the other hand, a major incident involving actual or potential death, injury or critical system failure may justify a detailed investigation led by senior management and with input from independent experts.
  • Competence - incident investigation is specialised work, therefore conveyors should ensure that investigations are carried out by people with the right knowledge and expertise. A variety of people and disciplines may need to be involved in a more complex investigation.
  • Managing the investigation - where possible, and particularly in more serious cases, there should be independent oversight by a senior manager or safety professional not directly involved in the investigation. They should monitor the quality of the investigation, verify that appropriate conclusions are drawn and have the credibility to challenge the investigators and make authoritative judgements.

Part 2 - suggested report headings and contents

All reports should include the following:

i) Brief description of the circumstances - this will be largely factual and, for simple investigations, may be brief. Possible headings include:

  • location / address;
  • date and time of event;
  • time notification received;
  • reported by;
  • details of notification ie fire / explosion / gas leak, any injuries;
  • notification to HSE - date / time / who by / who received at HSE / indication of proposed HSE action;
  • site arrival times;
  • persons, plant, premises and procedures involved;
  • site investigation - ie what was found and what was done.

For complex incidents, a timeline that identifies significant factors or events is useful. The front cover of the report should clearly state:

  • whether the incident falls under GSMR Regulation 7(12), 7(13) or 7(14);
  • if HSE are investigating, the name of the investigating inspector; and
  • the relevant RIDDOR reference number (where applicable).

ii) Causal factors - incidents rarely have a single cause and there are often underlying failures in the management system.  Good investigations identify both immediate and underlying causes, including human factors (see HSE publication HSG48 'Reducing Error and Influencing Behaviour' and the human factors in accident investigations pages of the HSE website).

Immediate causes may be easy to identify but underlying causes can be less obvious. For example, the immediate cause of an incident may have been an employee's failure to follow a procedure; however there may be a number of underlying factors, such as poor supervision, insufficient competence, equipment failure/unavailability, time pressure etc. If these issues are not considered, underlying failures that could lead to further incidents won't be put right. Employees may also be blamed unfairly, this damages trust and can have an adverse impact on the organisation's safety culture.

In complex investigations, more structured techniques can be used to identify underlying causes eg failure mode and effects analysis, fault tree analysis.

iii) Conclusions and recommendations - this should include a prioritised list of remedial actions and recommendations, with clearly allocated responsibilities and completion dates.  The report should also describe the monitoring and review process that will be used to check that actions are completed and confirm that they have achieved the desired effect.

How to make notifications and submit reports

The process for making RIDDOR reports is described in the RIDDOR web pages of the HSE website.

GSMR notifications under Regulation 7(12) and 7(13), and under Regulation 7(14) by gas suppliers, should be made to Energy Division - Gas and Pipelines (ED3) on: 020 3028 5001.

Out of hours notifications should be made to the HSE Duty Officer, who should be told that the incident is being notified to HSE under GSMR. If the Duty Officer cannot be reached, the Duty Press Officer should be notified.

GSMR investigation reports should be submitted electronically to the GSMR e-mail address: [email protected]

GSMR does not specify time limits for submitting GSMR reports but the time taken should be reasonable, given the nature of the investigation. As a guide, a relatively simple investigation report should be submitted within 28 days of the incident, and a more complex report that requires specialist input should be submitted within three months.

Contact details for GSMR notifications and reports

HSE (working hours)

Foundry House, 3 Millsands, Riverside Exchange, Sheffield, S3 8NH     
Telephone: 020 3028 5001
Email: [email protected]

Out of hours HSE Duty Officer

Telephone reports only  0151 922 9235  
If the duty officer is unobtainable please call the Duty Press Officer on 0151 922 1221

Advice on assessing gas releases from mains and services

The rate of gas release from a damaged pipe depends on many factors, including the gas pressure, the dimensions of the pipework, the characteristics of the hole/crack, the length of service to damage and the characteristics of the surrounding material.

The following tables have been derived from calculations in British Gas Research & Technology Report No ERS R5503 (June 1995) to help estimate gas releases from damaged pipes. Table 1 shows the flow rate of gas expected from a damaged pipe where the pipe diameter is more than twice the diameter of the hole. Tables 2 and 3 indicate the times taken under various conditions to release a reportable quantity of gas.  If the duration of a leak is known, the amount of gas likely to have been released can be estimated.

Table 1: Damaged Pipe (Pipe Diameter > 2x Hole Diameter) Flow Rates

Hole Dia." Hole Area LP 10" wg LP 15" wg MP 5psi MP 20 psi No column header
0.5 0.2 21 25 87 207 m3/hr
1 0.8 89 110 378 871  
2 3 356 442 1,512 3,485  
4 12 1.42 1,766 6,049 13,940  
10 75 8.900 11,040 37,800 87,130  

Table 2: Damaged Pipe (Pipe Diameter > 2x Hole Diameter) Times to Release 735 m3 (500kg)

Hole Dia." Hole Area LP 10" wg LP 15" wg MP 5psi MP 20 psi No column header
0.5 0.2 2,151 1,736 506 220 mins
1 0.8 496 401 117 51  
2 3 124 100 29 13  
4 12 31 25 7 3  
10 75 5 4 1 0.5  

Table 3: Damaged Pipe (Pipe Diameter > 2x Hole Diameter) Times to Release 14.7 m3 (10kg)

Hole Dia." Hole Area LP 10" wg LP 15" wg MP 5psi MP 20 psi No column header
U0.5 0.2 43.02 34.72 10.13 4.39 mins
1 0.8 9.91 8.02 2.33 1.01  
2 3 2.48 2 0.58 0.25  
4 12 0.62 0.5 0.15 0.06  
10 75 0.1 0.08 0.02 0.01  

Note: If the gas main is cracked, divide the gas main diameter by four and use this figure as hole diameter in the above tables.


  • 10" water gauge (wg) = 25 mbar
  • 15" wg = 37.5 mbar
  • 5 psi = 345 mbar
  • 20 psi = 1.38 bar

Map of Gas Distribution Network Operators

Gas is transported to premises in Great Britain by five Gas Distribution Network operators (GDNs). The map below shows their geographical operation and ownership along with the relevant lead inspection team within Energy Division - Gas and Pipelines.

UK map of the five Gas Distribution Network operators - Scotland Gas Networks PLC: ED 3.1; Northern Gas Networks Ltd: ED 3.3; Cadent Gas Ltd: North West - ED 3.3, West Midlands - ED 3.3, East of England - ED 3.2, London - ED 3.2; Wales and West Utilities Ltd: ED 3.2; and Sothern Gas Networks PLC - ED 3.2

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