The task guidance sheets are designed to provide guidance on the protection of human health against the harmful effects caused by high exposures to hazardous substances. However many substances may also pose fire or explosion hazards or may harm the environment if they escape from the factory. The equipment used to process the substances may also be harmful. Where appropriate flammability and explosivity needs are identified on the task guidance sheets.
To provide protection from harmful machinery, the guidance sheets often refer to a system of work called a 'permit to work' for maintenance activities. One of the key features of a permit to work system is a 'lock–out/tag-out' control system, which prevents the operation of machinery whilst maintenance is undertaken. The key features of this system are described in sheet S100.