 Studies by the UK Health and Safety Executive have shown that the most significant cause of the maintenance related accidents in the UK chemical industry was a failure to implement of effective permit to work systems.Common failures in control of work systems are a failure to follow the permit to work or isolation management procedures, risk assessments that are not suitable and sufficient to identify the risks, and/or the control measures and a combination of the two.Permit to work implementations usually use incompatible operations matrices.