This guidance covers all onshore equipment that provides the primary containment boundary to hazardous substances@ which will include pressure vessels@ relief streams@ atmospheric storage tanks@ reactors and pipework. It will cover machines such as pumps@ agitators@ valves and compressors in so far as they are required to maintain primary containment. It does not cover the maintenance of such machines necessary to ensure their continued operation. The hazardous substances considered includes those with the potential to cause harm (either to people and/or the environment) as a result of their toxicity@ flammability or other form of chemical reactivity (including explosives). In particular this includes the dangerous substances listed in the Control of Major Accident Hazards (COMAH) Regulations. The guidance is aimed at sites which handle process and store such dangerous substances. This includes establishments where the COMAH Regulations apply. It may also be relevant to sites outside the scope of COMAH where there are hazardous substances present. All those involved in some part in the management of mechanical integrity of plant and equipment should find the guidance relevant. This will include site operators@ inspection bodies (including competent persons@ as defined by relevant regulations) and those offering specialist services to the process.