Risk assessment is a necessary step in the management of risk. In the UK the general legislation requires duty holders to reduce risks to as low as is reasonably practicable (ALARP) and conduct a suitable and sufficient risk assessment for the purpose of identifying the measures to take to comply with the relevant statutory provisions. Risk assessment has a particularly important role where major accidents are possible and describing conformity with standards is not sufficient to demonstrate that all necessary measures have been taken. This paper is an attempt to clarify the important role of risk assessment and the various techniques available, particularly where the use of fully quantified risk assessment would not be proportionate to the scale of hazards and risks.