Incidents & Accidents · Mandatory · Construction

Dangerous Occurrence Report

A report for dangerous occurrences that must be notified to the HSE under RIDDOR 2013 Schedule 2. These include scaffold collapses, crane overturns, explosions, and other specified events regardless of whether anyone was injured.

Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. RIDDOR 2013 remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.

1. Dangerous Occurrences — Near Misses That Must Be Reported to HSE

Dangerous occurrences are RIDDOR-defined near-miss events so serious that HSE requires reporting even when no person was injured. The event type is the trigger — not whether anyone was hurt. A scaffold collapse of more than 5 metres is reportable whether or not anyone was beneath it.

The most frequent dangerous occurrences on construction sites include: scaffold collapse over 5m, unintended structural collapse, plant contacting overhead power lines, and fires causing more than 24 hours of site stoppage.

Report dangerous occurrences without delay — even if no one was injured

A scaffold collapsing at 6pm with no workers present is still reportable under RIDDOR if the scaffold was over 5 metres. The absence of injury does not remove the obligation. The scene must be reported and preserved. Clearing a collapsed scaffold before investigation destroys evidence that HSE may require.

2. Dangerous Occurrence Report — Content

Field	Content
Date/time/location	When and where the dangerous occurrence took place.
Type of DO	Category from RIDDOR Schedule 2. Specific description of the event type.
Description	Full narrative of events. What failed, collapsed, exploded, or made contact.
Persons involved	Were any persons affected? Names. If no injury — confirm explicitly.
Scene preservation	Has the scene been secured? Who is responsible for preservation?
Immediate action	Actions taken to make safe, provide first aid, evacuate, or contact emergency services.
RIDDOR report made?	Date/time of report. Reference number. Method: online or telephone.
Investigation	Has investigation commenced? Lead investigator. External investigation if HSE attends.
Reported by	Name, role, signature. Manager counter-signature.

3. Common Mistakes

Treating as a near miss and not reporting to HSE

The most common failure. Not recognising that an event falls within RIDDOR Schedule 2. Any scaffold collapse over 5m must be reported. Any plant contacting overhead power lines must be reported. Any structural collapse of 5 or more tonnes must be reported. The test is the event type, not whether anyone was hurt.

Disturbing the scene before investigation

The instinct is to make the area safe and restore work. This destroys evidence. The scene must be secured until the investigation team has documented all evidence. HSE may direct what can and cannot be moved, particularly for serious events.

No investigation after the RIDDOR report

The RIDDOR report fulfils the statutory notification obligation but does not substitute for the internal investigation required under MHSWR. Root causes must be identified, corrective actions implemented, and lessons communicated to the workforce.

Delay in reporting — waiting to see if HSE will find out

RIDDOR requires reporting without delay. Delayed or absent reporting is likely to be discovered through worker reports, media coverage, or emergency service logs. Discovery of deliberate delay results in more severe enforcement action.

Incorrect categorisation

The correct RIDDOR Schedule 2 category must be identified before submitting the report. An incorrect category or reporting a non-dangerous occurrence creates a confused record. If uncertain about the correct category, contact HSE on 0345 300 9923 for guidance.

4. Frequently Asked Questions

What scaffold collapse height triggers a RIDDOR dangerous occurrence?▾

Collapse or partial collapse of a scaffold more than 5 metres in height resulting in a substantial part falling. The 5m refers to the scaffold height. A partial collapse of a single board from a 2m scaffold does not qualify. Collapse of a significant section of a 6m facade scaffold does qualify. The test requires both height (over 5m) and that a substantial part fell.

What happens if HSE investigates?▾

HSE may attend the scene, interview witnesses, and examine evidence. They may serve an improvement notice, a prohibition notice, or initiate prosecution. The principal contractor must cooperate fully — obstruction of an HSE inspector is a criminal offence under HSWA 1974.

Is near contact with overhead power lines a dangerous occurrence?▾

Only if the plant actually made contact. RIDDOR Schedule 2 requires contact with an overhead line. Near contact without actual contact is not a RIDDOR dangerous occurrence but is a very serious near miss requiring thorough internal investigation and immediate corrective action.

Must dangerous occurrences be recorded as well as reported?▾

Yes. RIDDOR Reg 12 requires records to be kept for a minimum of 3 years. The online system provides a copy of the submitted report — this should be retained as the statutory record. The site should also maintain an internal dangerous occurrence report (G3) and record the event in the accident book even if no injury occurred.

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