Causes are likely to fall into five categories - task, material, environment, personnel, and management. You should look for causes in all five of those categories in every investigation you conduct. The Canadian centre for Occupational Health and Safety suggests s series of questions to ask, along with a "why" or "why not" for each one. These questions are only the guide. Circumstances at the time of the investigation may be the best guide as to what questions need to be asked.
Task:
- Was a safe work procedure being used?
- Has conditions changed to make the normal procedure substandard?
- Were appropriate tools and materials available?
- Were they used?
- Were safety devices working properly?
- Were lockout and/or tagout procedures used when necessary?
- Material:
- Was there an equipment failure? If so, what caused it to fail?
- Was the machinery poorly designed?
- Were hazardous substances involved?
- Were they clearly identified?
- Was a less hazardous alternative substance available?
- Was the raw material substandard in some way?
- Was personal protective equipment (PPE) called for?
- Was the PPE being used?
- Environment: (at the specific time of the incident)
- What were the weather conditions?
- Was housekeeping a problem?
- Was it too hot or too cold?
- Was noise a problem?
- Was there adequate light?
- Were toxic gases, dusts, or fumes present?
- Personnel:
- Were the employees experienced in the task being performed?
- Had they been adequately trained?
- Were they physically capable?
- What was the status of their health?
- Were they tired?
- Were they under stress (personal and/or work related)?
- Management:
- Were safety rules in effect?
- Were they being enforced?
- Was adequate supervision given?
- Haze hazards been previously identified?
- Has procedures been developed to overcome them?
- Were substandard conditions corrected?
- Was regular maintenance of equipment carried out?
- Were regular safety inspections carried out?
NOTE: This is simply a list of suggested questions to ask, not a checklist to follow. It is better to approach your investigation with an open mind than to use a predetermined set of questions that maul not fit the circumstances.