2.2.6.4 Investigation checklists can be very useful in the early stages to keep the full range of enquiry in mind, but they cannot cover all possible aspects of an investigation, neither can they follow all individual leads back to basic causal factors. When checklists are used, their limitations should be clearly understood.
2.2.6.5 The initial stages of an investigation normally focus on conditions and activities close to the incident and only primary causes, also called "active failures", are usually identified at this stage. However, conditions or circumstances underlying these causes, also called "latent failures", should also be investigated.
2.2.6.6 A factor to consider during an investigation is recent change. In many cases it has been found that some change occurred prior to an occurrence which, combining with other causal factors already present, served to initiate the occurrence. Changes in personnel, organisation, procedures, processes, and equipment should be investigated, particularly the hand-over of control and instructions, and the communication of information about the change to those who needed to know.
2.2.6.7 The effect of work cycles and work-related stress could have an impact on an individual's performance prior to an occurrence. The impact of social and domestic pressures (so-called error-enforcing conditions) related to an individual's behaviour should not be overlooked.
2.2.6.8 Information should be verified wherever possible. Statements made by different witnesses may conflict and further supporting evidence may be needed. To ensure that all the facts are uncovered, the broad questions of "who?, what?, when?, where?, why?, and how?" should be asked.
2.2.7 Conducting interviews
2.2.7.1 An interview should start with the introduction of the interviewing party, the purpose of the investigation and of the interview, and the possible future use to be made of the knowledge and material obtained during the interview. Investigators should be guided by the requirements of national law regarding the presence of legal advisers or other third parties during an interview.
2.2.7.2 People should be interviewed singly and be asked to go step-by-step through the events surrounding the occurrence, describing both their own actions and the actions of others. The interviewer should take into account the culture and language of the interviewee.
2.2.7.3 Notwithstanding any previously made written statements, the value of a witness's statement can be greatly influenced by the style of the interviewer, whose main task is to listen to the witness's story and not to influence him/her.
2.2.7.4 If the investigation is a team effort, great care should be taken not to make a witness feel intimidated by too many interviewers. Experience has shown that interviews can be effectively conducted by two interviewers and if appropriate, the witness could be accompanied by an independent "friend".
2.2.7.5 It should be remembered that an investigation team is often seen as having a prosecuting role, and there may be reluctance to talk freely if interviewees think they may incriminate themselves or their colleagues. An investigator is not in the position to give immunity in return for evidence, but should try to convince interviewees of the purpose of the investigation and of the need for frankness.
