Dangerous occurrences

Dangerous occurrences are certain incidents with a high potential to cause death or serious injury. Those incidents which must be reported are listed in Schedule 2 of the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations (RIDDOR).

Reporting these occurrences:

  • allows enforcing authorities to learn about what happened and why
  • helps regulators and businesses prevent accidents

This page explains which sections in Schedule 2 of RIDDOR apply for each type of dangerous occurrence. The relevant paragraph numbers are provided to help you find the right section of the Schedule.

Reporting dangerous occurrences does not require complex analysis. It is more about making a reasonable judgement on whether the incident caused a real risk of harm. This allows for quick reporting and ensures valuable information is not lost.

The term ‘plant’ is used throughout Schedule 2. It is defined in the Health and Safety at Work Act as including any machinery, equipment or appliance.

General incidents at all workplaces

Paragraphs 1-23 of Schedule 2 cover reportable dangerous occurrences at all workplaces. There is a separate section on this page for incidents at all workplaces except those offshore.

Lifting equipment (paragraph 1)

The definition covers the collapse or overturning of any lifting equipment, or the failure of any load-bearing part, whether it is used for lifting goods, materials or people.

It does not cover the failure of:

  • ancillary equipment, such as electric operating buttons or radius indicators, or
  • lifting accessories, such as chains and slings

Failure means components which break down mechanically during the normal operation of the lifting equipment, rather than accidental or deliberate damage.

Incidents involving cranes must be reported whatever work is being done, and reports must not be restricted to those involving lifting and lowering. For example, a collapse or overturning when a machine is being used for demolition activities must be included.

Lifting equipment includes machinery such as bored piling rigs and percussion piling rigs.

Pressure systems (paragraph 2)

The definition in paragraph 2 of the Schedule covers the failure of a pressure system (other than a pipeline) with the potential to cause the death of any person. It applies to any such vessel, whatever its contents.

These incidents include:

  • scaldings or burns caused by contact with steam, hot water, other hot liquids, liquors, hot products or hot substances
  • immersion in liquids
  • splashing with toxic chemicals

Other examples of incidents which might be notifiable as having ‘potential to cause death’ would be those where a person was either struck by, or could have been struck by, a projectile emitted from the failure of a closed vessel or pipeline under pressure.

In an explosion, this might be:

  • a fixture or component
  • the vessel or pipeline itself
  • a secondary projectile due to structures being destroyed close to the vessel, for example falling debris such as masonry or window glass, or shrapnel from buildings or other structures

Overhead electric lines (paragraph 3)

Incidents involving any unintentional contact between plant or equipment and overhead electric lines are reportable when they involve:

  • contact with an uninsulated overhead electric line where the voltage exceeds 200 volts, or
  • close proximity with an electric line, which causes an electrical discharge

Examples of these kinds of reportable incidents are:

  • accidental contact between a mobile crane or a vehicle and an overhead line
  • accidental contact with an overhead line by something being carried or lifted
  • the collapse of something (for example an engineering structure) across an overhead line

Electrical incidents causing explosion or fire (paragraph 4)

Where an electrical short circuit or overload causes the failure of electrical equipment (including through accidental damage) and results in a fire or explosion, this is reportable if:

  • the equipment concerned is put out of action and is unusable for over 24 hours
  • the occurrence had the potential to cause the death of any person

The incident is reportable even if the system in which the damaged equipment was installed is put back into service, using new equipment, within 24 hours. An assessment should be made of how long a repair to the damaged equipment would have taken.

Repair time does not include incidental time delays, for example caused by travelling to repair plant in remote locations, or with sourcing parts.

For fires and explosion that do not relate to electrical incidents, please refer to paragraph 25 of the Schedule.

Explosives (paragraphs 5-9)

The types of incidents that must be reported involving explosives are covered in paragraphs 5-9 of the Schedule.

These dangerous occurrences refer to:

  • specific incidents arising in work situations from the use of explosives
  • unintentional events at premises where explosives are manufactured or stored

There is more guidance on explosives.

Biological agents (paragraph 10)

You must report any accident or incident which results, or could have resulted, in the release or escape of a biological agent likely to cause severe human infection or illness.

A ‘severe human infection or illness’ is one caused by biological agents in Hazard Groups 3 and 4 as defined in Schedule 3 of the Control of Substances Hazardous to Health Regulations (COSHH).

HSE has guidance on clinical laboratories.

There is advice on RIDDOR in health and social care.

Radiation generators and radiography (paragraph 11)

You must report any malfunction of:

  • a radiation generator or its ancillary equipment used in fixed or mobile industrial radiography, irradiating food or processing products by irradiation, which causes it to fail to de-energise at the end of the intended exposure period
  • equipment used in fixed or mobile industrial radiography or gamma irradiation, which causes a radioactive source to fail to return to its safe position by the normal means at the end of the intended exposure period

'Radiation generator' means any electrical equipment emitting ionising radiation and containing components operating at a potential difference of more than 5kV.

The processes covered include all types of industrial radiography – such as radiography in fixed enclosures, site radiography, and radiography in closed cabinets.

Irradiating and processing products by irradiation are high-dose treatments and this covers panoramic systems as well as self-contained units. In each case, it is the failure of the means for de-energising the radiation generator at the end of the intended exposure period that constitutes the dangerous occurrence.

Incidents where equipment malfunction causes a radioactive source to fail to return to a safe (shielded) position at the end of the intended exposure period are also reportable. The sources will commonly be gamma ray sources, but in industrial radiography they could be beta ray or neutron sources.

The processes covered include all types of industrial radiography, and use of gamma irradiation equipment (panoramic or self-contained). The type of equipment must mean:

  • the source goes from a safe state to an exposed state in use
  • operation of manual or automatic control systems normally returns the source to its shielded state

Any malfunction affecting the equipment and its control system causing the failure of the source to return to this state at the end of the intended exposure period constitutes a dangerous occurrence.

These incidents must be reported whether or not anyone is exposed to ionising radiation as a result of the incident occurring, other than those incidents which must be reported under the Ionising Radiations Regulations (IRR).

Where a report is required under IRR, there is no need to also report under RIDDOR, except in relation to offshore workplaces.

Breathing apparatus (paragraph 12)

You must report the malfunction of breathing apparatus:

  • where the malfunction causes a significant risk of personal injury to the user
  • during testing immediately before use, where the malfunction would have caused a significant risk to the health and safety of the user had it occurred during use – there are separate requirements for mines (see paragraph 39 of the Schedule)

This definition applies to breathing apparatus used under water as well as in contaminated atmospheres or where there may be a lack of oxygen. It refers to a session of use of the apparatus during, or immediately before, a malfunction is detected.

The malfunction may be present and be detected immediately before the session (including any testing by the wearer immediately before use), or it may occur at some point after the session has started.

The term 'malfunction' does not include leakage into a face mask due to a poor fit or a failure caused by an external source, such as damage due to entanglement or falling debris.

Diving operations (paragraphs 13-17)

You must report the failure, damaging or endangering of:

  • any life support equipment, including control panels, hoses and breathing apparatus
  • the dive platform, or any failure of the dive platform to remain on station which causes a significant risk of personal injury to a diver

You must also report:

  • the failure or endangering of any lifting equipment associated with a diving operation
  • a diver being trapped
  • any explosion in the vicinity of a diver
  • any uncontrolled ascent or any failure to decompress which causes a significant risk of personal injury to a diver

Specialist advice is available from HSE diving inspectors by e-mail at [email protected].

Collapse of scaffolding (paragraph 18)

You must report the complete or partial collapse (including falling, buckling, or overturning) of:

  • a substantial part of any scaffold more than 5 metres high
  • any supporting part of any slung or suspended scaffold which causes a working platform to fall (whether it is in use or not)
  • any part of any scaffold where there would be a significant risk of drowning to anyone falling from it

The incidents covered here are those involving any 'scaffold'. This includes any tower, trestle, slung or suspended scaffold.

The figure of 5 metres refers to the height of the scaffolding itself from its base and not necessarily to the distance between the top of the scaffold and the ground.

Incidents involving the failure of the suspension arrangements of slung or suspended scaffolds are covered if the failure causes a working platform or cradle to fall.

Reportable failures of suspension arrangements would include failures of outriggers, roof rigs or suspension ropes or winches.

Train collisions (paragraph 19)

You must report the collision of a train with any other train or vehicle, other than a collision reportable under Part 5 of the Schedule, which could have caused the death, or specified injury, of any person.

RIDDOR therefore only applies to collisions between rail-mounted locomotives or trains and other vehicles within factory or dock premises, or at construction sites, mines or quarries.

Part 5 of the Schedule refers to 'relevant transport systems', which are covered by paragraphs 48-74. Those type of incidents are reportable to the Office of Rail and Road (ORR).

Onshore and offshore wells (paragraph 20)

The incidents listed in the Schedule are reportable for all wells, both onshore and offshore, that are drilled for the exploration or exploitation of oil or gas. This includes production of coal bed methane for commercial purposes.

They also apply to wells drilled in connection with the exploitation of oil or gas, for example those used to support reservoir pressure through water or gas injection.

Reports are required for:

  • all blowouts, including those of limited duration
  • all incidents where a blowout preventer is closed or a diverter is operated to control an unplanned flow into the well-bore from the adjoining formations, but not where flow is planned as part of an operation. This includes 'underground blowouts', where the well fluids flow to subsurface rock formations rather than to the surface

Reports are not required where:

  • flow is due solely to variations in the density of fluid across pipe installed in the well bore, commonly known as 'u-tubing'
  • it is known that mud previously lost to the formation is subsequently returned, commonly known as 'ballooning' or 'breathing'

You should report failures of the primary pressure containment envelope of a well or of safety devices, namely blowout preventers or surface, subsea and subsurface safety valves, where there is a major loss of pressure integrity requiring immediate remedial action.

It is not necessary to report minor leaks or failures found and rectified during routine maintenance, including replacement of worn components. However, significant leakages around a well of hydrocarbon gas from shallow formations should be reported.

All unplanned well intersections, where a well is unintentionally drilled into an existing one, are reportable. 'Near misses' should also be reported if normal drilling operations have to be interrupted to take remedial action to reduce the risk of collision.

Onshore and offshore pipelines or pipeline works (paragraphs 21-22)

The incidents listed in the Schedule are reportable for both onshore and offshore pipelines or pipeline works.

The phrase 'accidental or uncontrolled release' used in the Schedule is not intended to include minor leaks from pipelines, for example small leaks from valve stems, flanges etc. However, sudden or uncontrolled escapes requiring immediate attention or action should be reported.

Examples of reportable damage with the potential for harm would include gouging, denting, buckling etc caused by external interference requiring immediate action. Such damage may or may not have resulted in any escape of the pipeline contents.

Shutdown following discovery of substantial internal or external corrosion, so it would not be safe to continue operating the pipeline, should also be reported.

External coating damage without damage to the underlying substrate would not be reportable.

Examples of reportable occurrences would include movement of offshore pipelines following development of critical 'spans' and subsequent instability or displacement due to wave action or boat impact.

Occurrences that are not reportable include:

  • spans detected and rectified as a result of routine inspection activities
  • landslips, subsidence etc onshore, in the vicinity of pipelines, and similar movement in the seabed.

The following types of pipeline are not covered by these requirements as provided by a RIDDOR Exemption Certificate:

  • a drain or sewer
  • any pipe used to provide heating or cooling, or for domestic purposes
  • a pipe used in the control or monitoring of plant
  • a pipe used for the conveyance of air, water-vapour or steam
  • a water pipe, other than when used for the purposes of injecting water into an underwater well or reservoir containing mineral resources
  • a pipeline contained wholly within the premises of a single undertaking
  • a pipeline contained wholly within a caravan site
  • a pipeline contained wholly within land classes as a railway asset
  • any part of a gas-supply pipeline which is downstream of an emergency control

Incidents at all workplaces except those offshore

Paragraphs 23-27 of Schedule 2 cover incidents you must report unless you are working at an offshore workplace. There is a separate section on this page for incidents at offshore workplaces.

Structural collapse (paragraphs 23-24)

Only structural collapses associated with ongoing construction, maintenance and demolition work are required to be reported under the definition in paragraph 23: ‘the unintentional collapse or partial collapse of:

  • any structure, which involves a fall of more than 5 tonnes of material, or
  • any floor or wall of any place of work’

However, the requirement in paragraph 24 to report ‘unintentional collapses of partial collapse of any falsework’ applies whether construction work is taking place or not.

'Falsework' means any temporary structure used to support a permanent structure during its erection and until that structure becomes self-supporting.

Explosion or fire (paragraph 25)

This dangerous occurrence covers fires and explosions at work premises. The plant referred to includes any machinery, equipment or appliance.

Examples of the type of incident which would be reportable are:

  • any fire at a factory or office building, causing the suspension of work activities for more than 24 hours, or
  • an explosion involving dust in a pneumatic conveying system, causing stoppage of the conveying plant for more than 24 hours

The incident is not reportable if either the plant or the work activity in those premises where the fire or explosion occurred has not resulted in a stoppage or a suspension of normal work for more than 24 hours.

Release of flammable liquids and gases (paragraph 26)

This covers releases of flammable liquids or gases (for example due to the sudden failure of a storage vessel) where the release, if ignited, would cause a major explosion or fire.

'Flammable' includes those substances classified as highly flammable or extremely flammable.

If you are the responsible person, you should make a reasonable judgement about the quantity of flammable liquid or gas released.

Detailed calculations are not required, but where it is probable that the quantities released are within the categories set out in paragraph 26, you should make a report.

Hazardous escapes of substances (paragraph 27)

This dangerous occurrence only applies to the hazardous escape of substances in the workplace.

Failing to contain substances on a vehicle is only reportable if the failure occurs while the vehicle is at a workplace (for example during loading or unloading).

There is legislation which covers hazardous substances being transported. HSE has produced guidance on the carriage of dangerous goods.

The substances covered by this dangerous occurrence may be in any form such as a liquid, solid (for example a powder), gas or vapour. This may include:

  • substances hazardous to health (for example asbestos, phosgene, toluene diisocyanate), or
  • substances which may be either corrosive or potentially hazardous due to their temperature or pressure (for example nitric acid, molten metal, liquid nitrogen)

Examples of the kinds of incident covered are:

  • escapes due to the failure or breakage of plant, pipes, equipment or apparatus
  • failures of process control
  • the operation of a relief valve or bursting disc where the escaping substance is not safely controlled or directed
  • spillages from containers and equipment

You are not required to report releases from plant etc when they are controlled enough to ensure no one is at risk during normal operation or maintenance. Examples include during sampling, packaging or draining of lines.

In some cases, deciding whether an incident is reportable will be straightforward. For example, you must report a person being exposed to a hazardous substance which exceeds established safe limits, such as a workplace exposure limit.

However, most incidents require more judgement. Factors you could consider include:

  • the nature of the substance and its chemical, physical and toxicological properties
  • the amount which escaped and its dispersal
  • whether people were, or could foreseeably have been, exposed to a significant risk as a result of the escape

Incidents in mines

Paragraphs 28-46 of Schedule 2 cover the following types of incidents in mines:

  • fires or ignition of gas
  • escapes of gas with solid matter
  • failures of plant or equipment
  • breathing apparatus
  • emergency escape apparatus
  • inrushes of gas or flowing material
  • locomotives
  • falls of ground
  • accidents causing specified injuries

HSE mines inspectors can give specialist advice on dangerous occurrences reportable in mines.

If you have a concern in relation to health and safety at a mine you can tell HSE about the issue directly.

Incidents at quarries

Paragraphs 47-53 of Schedule 2 cover the following types of incidents in quarries:

  • collapse of storage bunkers
  • sinking of craft
  • projection of substances outside quarry
  • misfires
  • insecure tips
  • movement of slopes or faces
  • explosion or fire in vehicles or mobile plant

HSE quarries inspectors can give specialist advice on dangerous occurrences reportable in quarries.

If you have a concern in relation to health and safety at a quarry you can tell HSE about the issue directly.

Incidents on relevant transport systems

Paragraphs 54-74 of Schedule 2 cover incidents on relevant transport systems.

A relevant transport system is:

  • a railway
  • a tramway as defined by regulation 2(1) of the Railways and Other Guided Transport Systems (Safety) Regulations 2006
  • a trolley vehicle system as defined by section 67 of the Transport and Works Act 1992, except when it operates on a road
  • any other system using guided transport, as defined by regulation 2(1) of the 2006 Regulations

These incidents are reportable to the Office of Rail and Road (ORR), who publish their own ORR guidance on RIDDOR.

Incidents at offshore workplaces

Paragraphs 75-87 of the Schedule cover the dangerous occurrences that are only reportable if they occur at an offshore workplace. This is defined in regulation 2 of RIDDOR and includes:

  • wells
  • offshore pipelines
  • offshore installations associated with the exploitation of mineral resources

Offshore windfarms and other renewable energy installations are not included.

Some incidents only apply at offshore installations. In this section 'offshore installation' includes subsea units, but excludes:

  • tied back wells
  • pipelines and associated apparatus or works within 500 metres of the installation's main structure
  • fixed towers not associated with oil and gas activities

There is separate guidance on reporting incidents (under Schedule 2) at:

  • onshore and offshore wells (paragraph 20)
  • onshore and offshore pipelines or pipeline works (paragraphs 21-22)

Reporting offshore incidents

To report on an offshore-related issue please use the Report of an Oil and Gas Incident (ROGI) form.

The form allows reporting under all the relevant legislation and requirements including RIDDOR.

Specialist advice on reporting requirements offshore is available.

Release of petroleum hydrocarbon (paragraph 75)

This section of the Schedule only refers to confirmed, unintentional releases of petroleum hydrocarbons. Suspected releases which turn out to be false alarms are not reportable.

To be reportable, releases must also lead to one of the following outcomes:

  • a fire or explosion – this includes all types of fires, whether flash, jet or pool, regardless of how long it burns for
  • necessary preventive or evasive action to limit the consequences of the potential fire or explosion

You do not need to report small gas leaks detected during routine monitoring and maintenance, for example checking on valves, seals etc where there is limited risk to people. To be reportable, the action must intend to prevent or limit the consequences of a potential fire or explosion.

Simply taking action to confirm a release following an alarm, for example by instrument reading that requires no further action, would not be reportable. However, taking action to confirm a release may precede more direct, reportable action.

Examples of actions when the release is reportable are:

  • an emergency stop of individual plant, either automatically or by operator intervention, to control leakage of process or non-process hydrocarbons
  • permit-to-work following confirmation of a hydrocarbon release with a potential for fire or explosion
  • operation of deluge, fixed fire-fighting system, blowdown etc or other preventive or limiting measures as a result of a confirmed hydrocarbon release
  • general shutdown, muster, evacuation of the area, or any combination of these actions following a confirmed release
  • the potential to cause death or major injury to any person

Hydrocarbon releases which are not covered above, but are also reportable are:

  • when there is cause for concern, for example when they involve high hydrogen sulphide (H2S) toxicity, or
  • where the release is dispersed or exhausts a limited inventory before action can be taken

Fire or explosion (paragraph 76)

Any fire or explosion at an offshore installation, other than one caused by the release of petroleum hydrocarbon, is reportable when it results in stopping plant or suspending normal work.

This covers fires or explosions, such as:

  • hydrocarbon releases from flares, vents or diverters which exceed operational limits
  • inadvertent internal combustion of unspent fuels within turbines or of flame/explosion propagation within flare systems
  • fires or explosions involving wood, paints, explosives etc

Release or escape of dangerous substances (paragraph 77)

Unintentional or uncontrolled release or escape of any substance on or from an offshore installation is reportable when it could cause a significant risk of personal injury. This does not include release of petroleum hydrocarbon.

Releases of substances such as stored chemicals, superheated steam, or H2S are reportable where they don’t involve hydrocarbons.

Collapses (paragraph 78)

Any unintentional collapse or partial collapse of any offshore installation or of any plant on an offshore installation is reportable when it jeopardises the overall structural integrity of the installation.

Equipment (paragraph 79)

The failure of equipment required to maintain a floating offshore installation on station is reportable when it could cause a specified injury or the death of any person.

Dropping objects (paragraph 80)

Dropping any object on an offshore installation or on an attendant vessel or into the water adjacent to an installation or vessel is reportable when it could cause a specified injury or the death of any person.

Weather damage (paragraph 81)

Any damage to or on an offshore installation caused by adverse weather conditions is reportable when it could cause a specified injury or the death of any person.

Collisions (paragraphs 82-83)

Any collision between a vessel or aircraft and an offshore installation is reportable when it causes damage to the installation, the vessel or the aircraft.

Any occurrence with the potential for a collision between a vessel and an offshore installation is reportable where, had a collision occurred, it might have jeopardised the overall structural integrity of the installation.

It will not always be possible to accurately estimate whether a collision could have occurred or what the consequences might have been. HSE mainly wants to know about incidents where the dutyholder identifies a significant risk to the installation.

Subsidence or collapse of seabed (paragraph 84)

Any subsidence or collapse of the seabed likely to affect the foundations or the overall structural integrity of an offshore installation is reportable.

Loss of stability or buoyancy (paragraph 85)

Any incident which causes the loss of stability or buoyancy of a floating offshore installation is reportable.

Evacuation (paragraph 86)

Any partial or complete evacuation of an offshore installation is reportable when in the interests of safety.

Do not report a complete or partial evacuation if it is a response to an incident that is reportable separately under RIDDOR (such as a fire or explosion).

This definition does not cover exercises or precautionary measures.

Falls into water (paragraph 87)

Any person falling into water from more than 2 metres is reportable.

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Updated 2024-06-04