Background Safety rules continue growing rapidly, as if constraining human behaviour was the unique avenue for reaching ultimate safety. Safety rules are essential for a safe system, but their multiplication can have counterproductive effects.

Objective To monitor, in an anaesthesia ward, compliance with a process-oriented safety rule, and understand barriers and facilitators which help and hinder physicians from following guidelines.

Methods The rule stipulated that the day before surgery anaesthetists had to record in the patient's file the drugs to be used for the anaesthesia (induction, maintenance, airway control). Compliance was assessed before introduction of the rule, immediately after, at 6 months and at 12 months. All medical staff were blinded to the protocol.

Results 717 patient records were included. The results showed an initial compliance with policy, reaching 86% for some items (never 100%). Reduction began within 6 months and returned almost to initial levels within a year. One individual showed poor compliance throughout the study but even initially compliant doctors experienced a reduction. Compliance was higher for complex surgery but lower for unscheduled surgery and when job pressure was greater.

Conclusions Compliance eroded over time. A major trigger of erosion seemed to be lack of continued compliance by a senior member of staff. Rules and procedures constitute fragile safety barriers, and it may be better to forego introducing a new safety rule if it is not considered as a priority by staff and is therefore vulnerable to sacrifice in case of conflict with competitive demands.