The Contractors Health and Safety Assessment Scheme guarantees contractors are compliant with core H&S criteria. Members are required to meet criteria described in the CDM regulations through assessment of their H&S policy to  improve health and safety standards across the UK.​ Assessors consider each organisation on an individual basis, taking into account specific arrangements and whether they are adequate.

The CHAS health and safety assessment scheme is a pre-approval scheme to allow contractors to show potential clients that they meet the required health and safety standards.

The main purpose of CHAS is to avoid repeated applications by suppliers and contractors to become approved as local authority suppliers and to improve health and safety in small to medium sized businesses. Whilst the CHAS assessment scheme is a local authority and government backed scheme, it can be used by any organisation looking to short list suppliers and contractors and can save time and money for all parties.