# Pin index safety system

In the WHO-UNICEF oxygen therapy device specifications (2019), the Pin Index Safety System (PISS) is a cylinder valve connection in which the pin arrangement is unique for each gas and the holes on the cylinder valve must correspond with the pins, to ensure the correct gas is connected to the regulator or other equipment.

ISO 407:2023 (edition 5, July 2023), which replaced the withdrawn ISO 407:2021, applies to pin-index yoke-type valve connections for medical gas cylinders with a working pressure up to 200 bar or a test pressure up to 300 bar, or both. ISO notes that this connection is used mainly on small cylinders, of 5 l or below. The standard specifies basic dimensions, alternative designs of the yoke-type connection and the dimensions and positions of the holes and pins for gases and gas mixtures.

WHO, in Foundations of medical oxygen systems (2023), contrasts pin-index valves, which only accept the pressure regulator with the correct pin, with bullnose valves, which use non-interchangeable screw threads and are the most common valves on larger cylinders. In the WHO-UNICEF 2019 table of common cylinder sizes, D and E cylinders have pin-index valves to ISO 407 and J cylinders a pin-index side spindle valve. HTM 02-01 (2026), the NHS England guidance, says pin-index valves with a side spindle (J-size oxygen and medical air for manifolds) should be operated with the correct key.

WHO's Foundations of medical oxygen systems (2023) states that a foolproof system of gas-specific wall outlets supplements, but does not replace, the pin-index safety system.

## Sources

- [WHO-UNICEF, Technical specifications and guidance for oxygen therapy devices (2019), section 3 and Table 3.2](https://iris.who.int/server/api/core/bitstreams/5a996b5a-6803-486e-bccb-98efc398118d/content)
- [ISO 407:2023 Small medical gas cylinders, Pin-index yoke-type valve connections (iso.org summary)](https://www.iso.org/standard/85829.html)
- [WHO, Foundations of medical oxygen systems (2023), sections 2.7 and 2.9](https://iris.who.int/server/api/core/bitstreams/4ad6f5fd-089e-4142-8439-b64e98d816d8/content)
- [NHS England, HTM 02-01 (2026) Part B](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-b-operational-management-aug-26.pdf)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/glossary/pin-index/