impairment, a lack of concentration or awareness or compromised mobility. Audiometry (hearing test). This must be undertaken using equipment that conforms to the appropriate standards and guidelines specified with regular recorded calibration and maintenance. The subject should meet specific standards. Vision testing. This is undertaken under controlled conditions to meet specified visual standards. A clinical examination includes the following: a) Blood pressure estimation b) Physical examination, where appropriate, c) Urine testing, screening for some specific medical disorders. Where an individual fails to meet the specific medical standards it is, sometimes possible with the written agreement and co-operation of management and occupational health to implement a system of formal "safe working practices". This is so as not to discriminate unnecessarily against individuals with certain medical problems. The object of the medical assessment is to ensure that employers meet their duty of care so that individuals working in this potentially dangerous environment are not subject to increased risk of harm to themselves or their colleagues, or in some cases members of the public, due to any foreseeable underlying medical condition.. The work environment is in continual flux, and changes in acceptable risk are therefore variable. For this reason a provider of these services must be up to date with the policies and procedures within the industry and flexible to meet the changing demands required with transparency. Preserved railways Preserved railways often have their own volunteer PTS courses. Network Rail will not accept these PTS cards, and often vice versa. References External links Sentinel Railway People List of companies authorised to supply services to Network Rail NSAR NSAR-National Skills Academy for Rail, the Accreditation Body for Track Safety in the UK Rail transport in the United Kingdom Rail transport in the Republic of Ireland Health and safety in the United Kingdom