Investigation of workplace accidents

What is workplace accident investigation?

Investigating an accident involves gathering the facts, ordering them chronologically, identifying the contributing factors, and determining which failures in the preventative system allowed them to occur. The objective is preventative, not disciplinary: the investigation seeks causes, not culprits, and its outcome is a list of corrective measures with assigned responsibilities and deadlines. An investigation that merely describes the event and attributes it to negligence on the part of the injured person fails to fulfill its purpose.

Article 16.3 of Law 31/1995 obliges employers to conduct an investigation when harm to workers’ health has occurred or when, during health surveillance, there are indications that preventive measures are insufficient, in order to identify the causes of these incidents. The obligation does not differentiate based on severity: any accident resulting in harm must be investigated, although the depth of the analysis is determined according to the actual and potential severity.

Investigation is distinct from notification. Notification involves processing the workplace accident report through the Delt@ system and, when applicable, informing the labor authority of the incident. The Order of December 16, 1987, establishes a maximum period of five business days for reporting accidents resulting in sick leave, counted from the date of the accident or the date of the sick leave (Article 3.a), and a period of twenty-four hours for urgent notification to the labor authority of serious, very serious, fatal accidents, or accidents affecting more than four people (Article 6). Investigation involves internally analyzing what happened. Both obligations coexist, and neither replaces the other.

What accidents and incidents are being investigated

At a minimum, all accidents resulting in harm to health, whether or not they result in lost work time, must be investigated. Good practices and the ILO-OSH 2001 guidelines extend the investigation to incidents without harm, especially those with high potential for harm, because they share common causes with accidents and allow for intervention before injury occurs.

• Accidents resulting in lost work time. Complete investigation, including sequence reconstruction and cause analysis.
• Accidents without lost time and commuting accidents with injury. Investigation provided, focusing on factors that the company can control.
• High-potential incidents. Events without harm that in other circumstances would have caused a serious accident; they are investigated as if they had caused one.
• Occupational diseases and injuries detected through health surveillance require analysis of exposure and working conditions, not a single isolated incident.

The decision of what is investigated and how deeply should be defined in the company’s procedure, so that it does not depend on the judgment of each manager at any given time.

How the investigation is conducted: phases

1. Immediate action: attend to the injured person, control the remaining risk and preserve the scene as much as possible.
2. Information gathering: site visit, photographs, measurements, job documents (evaluation, instructions, permits, maintenance, training) and interviews with the affected person, witnesses and managers, in a climate that does not seek to assign blame.
3. Reconstruction of the sequence of events, separating proven facts from interpretations.
4. Analysis of causes with a defined method: cause tree, cause and effect diagram or other systematic method that reaches the organizational failures, not just the immediate fact.
5. Definition of corrective measures, prioritized according to the hierarchy of controls, with responsible party, deadline and resources, and integrated into the preventive planning.
6. Recording and communication: investigation report, information to worker safety representatives and the health and safety committee, and review of the risk assessment if the accident shows that it was insufficient.
7. Monitoring: checking that the measures are implemented and effective.

The INSST describes the fault tree analysis method in NTP 274 and the foundations of the investigation in NTP 442, both of which are standard references in Spain. The method chosen is less important than the discipline of applying it to identify the organizational causes.

Organizational application: who investigates and with what resources

The law assigns the obligation to the employer, who fulfills it through their prevention organization. In practice:

• Direct supervisor. Always involved; understands the actual task and is the one who will implement the measures. Investigating without him produces reports disconnected from the work.
• Internal or external prevention service. Provides the methodology, coordinates the investigation, and prepares the report; in serious accidents, it must lead the analysis.
• Worker safety representatives. They have the right to be informed of the damage caused and to accompany the technicians in the assessments and the inspectors on their visits; many companies incorporate them into the investigation team.
• Management. Approves measures that require investment and reviews serious accidents and trends.

The investigation procedure must establish deadlines (immediate start, report in days, not weeks), a report template, and a record that allows for trend analysis and demonstrates to the Labor Inspectorate that the obligation has been met. Digital systems facilitate registration, the approval process for measures, and traceability, but they do not replace site visits or interviews.

Limits and common mistakes

1. Focusing on the immediate cause (“he wasn’t wearing gloves”, “he got distracted”) without asking why that behavior was possible or common.
2. Turning the investigation into a disciplinary file reduces the reporting of incidents and the sincerity in interviews.
3. Investigate weeks later, when the scene has changed and witnesses have reconstructed their story.
4. Draft generic measures (“raise awareness”, “exercise extreme caution”) without changing working conditions.
5. Not reviewing the risk assessment even if the accident demonstrates that the risk was not correctly identified or assessed.
6. Confusing the Delt@ accident report with the investigation report; the former notifies, the latter analyzes.

The investigation also does not determine legal responsibilities: the actions of the Labor Inspectorate, the possible criminal investigation or the civil claim follow their own channels and can use the investigation report as evidence, which reinforces the need for it to be rigorous and truthful.

Regulatory framework in Spain

• Law 31/1995, articles 16.3, 23.1 and 36. Obligation to investigate damage to health, registration of accidents that have caused incapacity of more than one day and right of worker safety representatives to be informed about the damage caused.
• Royal Decree 39/1997, Article 6. Review of the risk assessment when damage to health has occurred.
• Order TAS/2926/2002 . Models of work accident report and Delt@ system for their electronic notification; the notification deadlines are set by the Order of December 16, 1987.
• NTP 442: Accident-incident investigation: procedure (INSST) . Phases, criteria and procedure model for investigation in the company.

The ILO-OSH 2001 guidelines recommend investigating accidents, illnesses, and incidents as part of reactive supervision, and doing so with worker participation. In other countries, this obligation has its own foundations and timeframes; in Colombia, for example, Resolution 1401 of 2007 regulates the investigation of workplace incidents and accidents.