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Dangerous Occurances

The list of dangerous occurrences in  RIDDOR is designed to obtain information primarily about incidents with a high potential to cause death or serious injury, but which happen relatively infrequently. Collecting the information allows the enforcing authorities to learn about the circumstances and their causes. This provides valuable information which both regulators and business can use to help prevent accidents.

For clarity, the guidance below includes relevant extracts from the Schedule requirements in bold.

Several types of dangerous occurrence require reporting in circumstances where the incident has the potential to cause injury or death. This assessment does not require any complex analysis, measurement or tests, but rather for a reasonable judgment to be made as to whether the circumstances gave rise to a real, rather than notional, risk. Such judgment allows for prompt reporting, and ensures that valuable information is not lost.

Schedule 2 lists three kinds of reportable dangerous occurrence:

  1. General (incidents occurring at any workplace)

These dangerous occurrences apply to all workplaces and include incidents involving, lifting equipment, pressure systems, overhead electric lines, electrical incidents causing explosion or fire, explosions, biological agents, radiation generators and radiography, breathing apparatus, diving operations, collapse of scaffolding, train collisions, wells and pipelines or pipeline works.


Lifting equipment

1 . The collapse, overturning or failure of any load-bearing part of any lifting equipment, other than an accessory for lifting.

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 failures of lifting accessories, such as chains and slings.

Failure in this context refers to components which suffer mechanical breakdown during the normal operation of the lifting equipment, as opposed to accidental or deliberate damage.

Incidents involving cranes must be reported irrespective of the nature of the work 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

2.  The failure of any closed vessel, its protective devices or of any associated pipework (other than a pipeline) forming part of a pressure system as defined by regulation 2(1) of the Pressure Systems Safety Regulations 2000, where that failure could cause the death of any person.

The definition 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.

Incidents requiring notification due to having 'the potential to cause the death of any person'. This includes scaldings or burns arising from contact with steam, hot water, other hot liquids, liquors, hot products or hot substances, and immersion in liquids or 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 the event of an explosion, this might be a fixture or component, the vessel or pipeline itself, or a secondary projectile arising from the destruction of structures close to the vessel, for example falling debris such as masonry or window glass, or shrapnel from buildings or other structures.

Overhead electric lines

3.  Any plant or equipment unintentionally coming into:

    1. Contact with an uninsulated overhead electric line in which the voltage exceeds 200 volts; or
    2. Close proximity with such an electric line, such that it causes an electrical discharge.

Examples of the kinds of incident relating to overhead electric lines, which must be notified and reported are:

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

Electrical incidents causing explosion or fire

4. Any explosion or fire caused by an electrical short circuit or overload (including those resulting from accidental damage to the electrical plant) which either:

    1. Results in the stoppage of the plant involved for more than 24 hours; or
    2. Causes a significant risk of death.

Where the failure of an item of electrical equipment (including as a result of accidental damage) results in a fire or explosion, the failure is reportable as a dangerous occurrence if the equipment concerned is rendered unusable for over 24 hours, or if the occurrence was one with 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. In such a case an assessment should be made of how long a repair to the damaged equipment would have taken had it been attempted?

Repair time does not include incidental time delays such as those associated with travelling to repair plant in remote locations, or with sourcing parts.


5.  Any unintentional:

    1. Fire, explosion or ignition at a site where the manufacture or storage of explosives requires a license or registration, as the case may be, under regulation 9, 10 or 11 of the Manufacture and Storage of Explosives Regulations 2005; or
    2. Explosion or ignition of explosives (unless caused by the unintentional discharge of a weapon, where, apart from that unintentional discharge, the weapon and explosives functioned as they were designed to)

except where a fail-safe device or safe system of work prevented any person being endangered as a result of the fire, explosion or ignition.

6. The misfire of explosives (other than at a mine or quarry, inside a well or involving a weapon) except where a fail-safe device or safe system of work prevented any person being endangered as a result of the misfire.

7. Any explosion, discharge or intentional fire or ignition which causes any injury to a person requiring first-aid or medical treatment, other than at a mine or quarry.

8 (1).  The projection of material beyond the boundary of the site on which the explosives are being used, or beyond the danger zone of the site, which caused or might have caused injury, except at a quarry.

(2) .In this paragraph, 'danger zone' means the area from which persons have been excluded or forbidden to enter to avoid being endangered by any explosion or ignition of explosives.

9. The failure of shots to cause the intended extent of collapse or direction of fall of a structure in any demolition operation.

These dangerous occurrences refer to specific incidents arising in work situations from the use of explosives, and unintentional events at premises where explosives are manufactured or stored. HSE Explosives Inspectors can give you more advice on this.

Biological agents

10.  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.

Severe human infection or illness means illness caused by biological agents in Hazard Groups 3 and 4 as defined in COSHH 2002, Schedule 3. These are set out in the latest edition of the Management, design and operation of microbiological containment laboratories, or are agents classified provisionally by an employer as being in one of those Hazard Groups. Riddor has more specialized guidance on how to apply this and other aspects of RIDDOR in the healthcare sector.

Radiation generators and radiography

11(1).  The malfunction of:

(a). A radiation generator or its ancillary equipment used in fixed or mobile industrial radiography, the irradiation of food or the processing of products by irradiation, which causes it to fail to de-energize at the end of the intended exposure period; or

(b).  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.

(2) In this paragraph, 'radiation generator' means any electrical equipment emitting ionising radiation and containing components operating at a potential difference of more than 5 kV.

There are two types of equipment covered here: radiation generators and equipment using radioactive sources (eg gamma ray sources). A radiation generator means any electrical equipment emitting ionising radiation and containing components operating at a potential difference of more than 5 kV.

The processes covered include all types of industrial radiography – such as radiography in fixed enclosures, site radiography, and radiography in closed cabinets. Irradiation of food and processing of 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 dangerous occurrences. The sources will commonly be gamma ray sources, but in industrial radiography could be beta ray or neutron sources. The processes covered once again include all types of industrial radiography, and use of gamma irradiation equipment (panoramic or self-contained). The type of equipment must be such that the source goes from a safe state to an exposed state in use, and 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 1999 (IIR). Where a report is required under IRR, there is no requirement to also report under RIDDOR, except in relation to offshore workplaces.

Breathing apparatus

  • 12 The malfunction of breathing apparatus:
         (a). Where the malfunction causes a significant risk of personal injury to the user; or
         (b). During testing immediately prior to use, where the malfunction would have caused a significant risk to the health and safety of the user had it occurred during use other than at a mine.

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 which 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

  • 13 The failure, damaging or endangering of:
    • any life support equipment, including control panels, hoses and breathing apparatus; or
    • 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.
  • 14 The failure or endangering of any lifting equipment associated with a diving operation.
  • 15 The trapping of a diver.
  • 16 Any explosion in the vicinity of a diver.
  • 17 Any uncontrolled ascent or any omitted decompression which causes a significant risk of personal injury to a diver.

Specialist advice is available from HSE Diving Inspectors.

Collapse of scaffolding

  • 18 The complete or partial collapse (including falling, buckling or overturning) of:
    1. a substantial part of any scaffold more than 5 metres in height;
    2. any supporting part of any slung or suspended scaffold which causes a working platform to fall (whether or not in use); or
    3. any part of any scaffold in circumstances such that there would be a significant risk of drowning to a person falling from the scaffold.

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

The figure of 5 metres used in relation to the height of scaffolding 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

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

This dangerous occurrence applies to railways which are not 'relevant transport systems.' It therefore applies to collisions between rail-mounted locomotives or trains and other vehicles within factory or dock premises. Incidents on relevant transport systems are covered by Schedule 2, Part 5 and further guidance is available from the Office of Rail and Road. [Link]


  • 20 In relation to a well (other than a well sunk for the purpose of the abstraction of water):
    1. a blow-out (which includes any uncontrolled flow of well-fluids from a well);
    2. the coming into operation of a blow-out prevention or diversion system to control flow of well-fluids where normal control procedures fail;
    3. the detection of hydrogen sulphide at a well or in samples of well-fluids where the responsible person did not anticipate its presence in the reservoir drawn on by the well;
    4. the taking of precautionary measures additional to any contained in the original drilling programme where a planned minimum separation distance between adjacent wells was not maintained; or
    5. the mechanical failure of any part of a well whose purpose is to prevent or limit the effect of the unintentional release of fluids from a well or a reservoir being drawn on by a well, or whose failure would cause or contribute to such a release.

These incidents are reportable for all wells, both onshore and offshore, drilled for the exploration or exploitation of oil or gas, including production of coal bed methane for commercial purposes. They also apply to wells drilled in connection with the exploitation of oil or gas, eg those used to support reservoir pressure through water or gas injection.

Reports are required for all blowouts, including those of limited duration.

Reports are required for 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, an effect commonly known as 'u-tubing'; nor where it is known that mud previously lost to the formation is subsequently returned, an effect commonly known as 'ballooning' or 'breathing'.

Failures of the primary pressure containment envelope of a well or of safety devices, namely blowout preventers or surface, subsea and subsurface safety valves, should be reported 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. Significant leakages around a well of hydrocarbon gas from shallow formations should also 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.

Pipelines or pipeline works

  • 21 In relation to a pipeline or pipeline works:
    1. any damage to, accidental or uncontrolled release from or inrush of anything into a pipeline;
    2. the failure of any pipeline isolation device, associated equipment or system; or
    3. the failure of equipment involved with pipeline works
  • which could cause personal injury to any person, or which results in the pipeline being shut down for more than 24 hours.
  • 22 The unintentional change in position of a pipeline, or in the subsoil or seabed in the vicinity, which requires immediate attention to safeguard the pipeline's integrity or safety.

The incidents listed are reportable for both onshore and offshore pipelines or pipeline works. The following types of pipeline are not covered by these requirements:

  • a drain or sewer
  • any pipe used to provide heating or cooling, or for domestic purposes
  • a pipes 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

The phrase 'accidental or uncontrolled release' is not intended to include minor leaks from pipelines, eg 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 such things as gouging, denting, buckling etc caused by external interference requiring immediate action. Such damage mayor may not have resulted in any escape of the pipeline contents. Shutdown following discovery of substantial internal or external corrosion, such that 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 not reportable would include spans detected and rectified as a result of routine inspection activities.

Such occurrences would include landslips, subsidence etc onshore, in the vicinity of pipelines, and similar movement in the seabed.

  1. Incidents occurring at any place other than an offshore workplace

These incidents do not require a report if they occur at an offshore workplace. They include structural collapses, explosions or fires, releases of flammable liquids and gases and hazardous escapes of substances.

The dangerous occurrences defined in Schedule 2 part 2 do not apply to offshore workplaces.

'Offshore workplace' is defined in regulation 2, and includes wells, offshore pipelines and offshore installations associated with the exploitation of mineral resources. Offshore windfarms and other renewable energy installations are not included.

Structural collapse

  • 23 The unintentional collapse or partial collapse of:
    1. any structure, which involves a fall of more than 5 tonnes of material; or
    2. any floor or wall of any place of work
  • arising from, or in connection with, ongoing construction work (including demolition, refurbishment and maintenance), whether above or below ground.
  • 24 The unintentional collapse or partial collapse of any falsework.

Only structural collapses associated with ongoing construction, maintenance and demolition work are required to be reported under paragraph 23. However, the paragraph 24 requirement to report unintentional collapses of 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

25 Any unintentional explosion or fire in any plant or premises which results in the stoppage of that plant, or the suspension of normal work in those premises, for more than 24 hours.

This definition covers serious fires and explosions at work premises. 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

Release of flammable liquids and gases

  • 26 The sudden, unintentional and uncontrolled release:
    1. inside a building
      1. of 100 kilograms or more of a flammable liquid;
      2. of 10 kilograms or more of a flammable liquid at a temperature above its normal boiling point;
      3. of 10 kilograms or more of a flammable gas; or
    2. in the open air, of 500 kilograms or more of a flammable liquid or gas.

This definition covers releases of flammable liquids or gases (eg 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.

Hazardous escapes of substances

27 The unintentional release or escape of any substance which could cause personal injury to any person other than through the combustion of flammable liquids or gases.

The substances covered by this definition may be in any form: liquid, solid (eg powder), gaseous or vapour and may include, eg:

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

This does not include hazardous escapes of substances occurring away from work premises, for example, during transport on the highway.

However, the uncontrolled escape of substances on or from a vehicle arising from the failure of containment would be covered if this incident took place during loading/unloading, or while the vehicle was present at work premises.

This definition includes incidents which present a fire or explosion hazard (eg combustible powders), but not in relation to releases of flammable liquids or gases, where the relevant thresholds in 26 [link to paragraph 26] are not exceeded.

Examples of the kinds of incident covered by the definition are escapes arising from 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, and spillages from containers and equipment.

Releases from plant etc during the normal course of operation or maintenance (eg during sampling, packaging or draining of lines) that are sufficiently well controlled to ensure that no person is put at risk would not be reportable.

In some cases, the decision as to whether or not an incident is reportable will be straightforward, eg if a person is exposed to a hazardous substance at a level which exceeds established safe limits (eg a Workplace Exposure Limit).

However, most incidents require judgement. Various factors are relevant including: the nature of the substance and its chemical, physical and toxicological properties, the amount which escaped and its dispersal, and whether people were, or could foreseeably have been, exposed to a significant risk as a consequence of the escape.


  1. Incidents occurring at specific types of workplace

Industries with specific requirements are: offshore workplaces, mines, quarries and relevant transport systems.

Weather damage

81 Any damage to or on an offshore installation caused by adverse weather conditions and which could cause a specified injury to, or the death of, any person.


  • 82 Any collision between a vessel or aircraft and an offshore installation which causes damage to the installation, the vessel or the aircraft.
  • 83 Any occurrence with the potential for a collision between a vessel and an offshore installation where, had a collision occurred, it might have jeopardised the overall structural integrity of the installation.

It will not always be possible to estimate with any accuracy whether a collision could have occurred or what the consequences might have been. HSE is primarily interested to know of incidents in which the dutyholder considers there was a significant risk to the installation.

Subsidence or collapse of seabed

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

Loss of stability or buoyancy

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


86 The partial or complete evacuation of an offshore installation in the interests of safety.

Full or partial evacuation may be a response to an incident separately reportable under RIDDOR (eg a fire or explosion), in which case it is not reportable under this paragraph. This definition seeks to include incidents not otherwise reportable, in which the risks are sufficient to warrant evacuation. It does not cover exercises or precautionary measures.

Falls into water

87 Any fall of a person into water from more than 2 metre