How are wrong gas connections prevented?

HTM 02-01 (2026), the NHS England guidance, makes identity of supply one of the basic principles of safety: every point where a user can connect equipment, and every user-replaceable component, has a gas-specific connection, also identified by symbol and colour. ISO 7396-1 likewise requires non-interchangeability between the components of different gas and vacuum systems.

1. At the outlet

Outlets (terminal units) to ISO 9170-1 are gas-specific, so a probe for one service cannot be used on another. They are gas-specific only within one connector style, because ISO 9170-1 does not set probe dimensions, so equipment needs probes of the style installed in the hospital.

2. Hoses and cylinders

Inside pendants and bed-head units, hoses connect with NIST (non-interchangeable screw-threaded) connectors to ISO 18082, so a hose can only be replaced by one for the same gas. Hose assemblies are covered by ISO 5359. Cylinders can use pin-index valves, as HTM 02-01 describes for J-size oxygen and medical air cylinders on manifolds, and WHO stresses that gas-specific outlets supplement the pin-index system and the other means of identification rather than replace them.

3. In the pipework and valves

HTM 02-01 calls it essential that there is no possibility of a cross-connection between any part of the system. Valve locks are keyed differently, and NIST lock nuts use a gas-specific lock for each gas. Blenders that could feed one gas into another system should not be connected to the pipeline but fed from a separate cylinder supply.

4. Proof by testing

• Under HTM 02-01, a cross-connection test at installation checks each gas in turn from the plant to the area valves and from the area valves to the outlets; it is repeated after any modification.
• The Quality Controller then analyses the gas at the outlets; where oxygen and nitrous oxide outlets share a bank, the oxygen is tested for the absence of nitrous oxide.
• In service, every outlet is tested quarterly with a blank probe for gas-specificity, mechanical function and leaks.

5. People and purchasing

Under HTM 02-01, the Designated Clinical Officer makes sure staff are trained in the correct connection and use of equipment, and the Authorised Person should be consulted before any equipment that connects to the pipeline is bought.