The Pin Index Safety System (PISS) is a means of connecting high pressure cylinders containing medical gases to a regulator or other utilization equipment. It uses geometric features on the

valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or Slurry, slurries) by opening, closing, or partially obstructing various passageways. Valves are technically Pip ...

and yoke to prevent mistaken use of the wrong gas. This system is widely used worldwide for anesthesia machines, portable oxygen administration sets, and inflation gases used in

surgery Surgery is a medical specialty that uses manual and instrumental techniques to diagnose or treat pathological conditions (e.g., trauma, disease, injury, malignancy), to alter bodily functions (e.g., malabsorption created by bariatric surgery s ...

Concept

The pin index safety system uses a face seal between the cylinder valve and the associated yoke clamp. There are two holes in specific positions on the cylinder valve body below the outlet port , in positions associated with the gas mixture, which prevent connection of the cylinder to a yoke or pressure regulator with a mis-matched set of pins. The holes accept pins 4 mm diameter by 6 mm long which are correctly aligned with the holes.

Pin index configurations

Each gas cylinder has a pin configuration to fit its respective gas yoke. Refer to the diagram for pin numbers; dimensions are in

millimeter 330px, Different lengths as in respect of the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 metre to 1 millimetre. The millimetre (American and British English spelling differences#-re, -er, i ...

s. * O₂: 2,5 * N₂O: 3,5 * Mixture of O₂ and N₂O (50% / 50%), commonly called

Entonox Nitrous oxide, as medical gas supply, is an inhaled gas used as pain medication, and is typically administered with 50% oxygen mix. It is often used together with other medications for anesthesia. Common uses include during childbirth, followin ...

: 7 (a single pin, located in the centre) *

Air An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

: 1,5 * Mixtures of CO₂ and O₂ with more than 7% CO₂: 1,6 * Mixtures of CO₂ and O₂ with less than 7% CO₂: 2,6 * He: No pin * Mixtures of O₂ and He with less than 80% He, commonly called

Heliox Heliox is a breathing gas mixture of helium (He) and oxygen (O2). It is used as a medical treatment for patients with difficulty breathing because this mixture generates less resistance than atmospheric air when passing through the airways of ...

: 2,4 * Mixtures of O₂ and He with more than 80% He: 4-6 * Cyclopropane: 3,6 * Ethylene: 1,3 * Nitrogen: 1,4 File:Pin index yoke connector for medical oxygen filling whip P8160068.jpg, Pin index yoke connector for medical oxygen filling whip File:Pin index yoke connector for medical oxygen filling whip P8160069.jpg, Detail of pin index yoke connector for medical oxygen File:Pin index medical oxygen cylinder valve P8160080.jpg, Pin index medical oxygen cylinder valve

International Standards

* International (

ISO The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries. Me ...

) and European ( CEN) Standard :*EN ISO 407 : Small medical gas cylinders - Pin-index yoke-type valve connections The pin index system is a safety system (PISS) designed to ensure the correct gas is filled into the correct cylinder, and that the cylinder will only connect to the correct equipment. The positions of the holes on the cylinder valve correspond with the pins fitted to the yoke attached to the equipment. The pin positions for each medical gas are unique. If an attempt is made to fit the wrong gas cylinder to the yoke a tight seal will not be made, as the pins cannot locate. The system requires a seal between the yoke and valve to prevent leakage. This is called a ''Bodok seal'', and is a moulded rubber washer (or

Neoprene Neoprene (also polychloroprene) is a family of synthetic rubbers that are produced by polymerization of chloroprene.Werner Obrecht, Jean-Pierre Lambert, Michael Happ, Christiane Oppenheimer-Stix, John Dunn and Ralf Krüger "Rubber, 4. Emulsion Rub ...

) supported by a metal rim.

Bodok seal

The Bodok seal is a specialised washer that ensures a gas-tight seal between the cylinder yoke or regulator of an

anaesthetic machine An anaesthetic machine (British English) or anesthesia machine (American English) is a medical device used to generate and mix a fresh gas flow of medical gases and inhalational anaesthetic agents for the purpose of inducing and maintaining ana ...

or any medical device requiring a gas supply, and a

gas cylinder A gas cylinder is a pressure vessel for storage and containment of gases at above atmospheric pressure. Gas storage cylinders may also be called ''bottles''. Inside the cylinder the stored contents may be in a state of compressed gas, vapor ov ...

. It was introduced along with the pin index safety system during the 1950s. Attachment and detachment of a gas cylinder leads to constant wear and tear, due in part to mechanical distress and to gaseous compression and expansion. Adiabatic effects in rapidly expanding compressed gases can generate very low temperatures, necessitating a sufficiently durable and cold-resistant material such as

neoprene Neoprene (also polychloroprene) is a family of synthetic rubbers that are produced by polymerization of chloroprene.Werner Obrecht, Jean-Pierre Lambert, Michael Happ, Christiane Oppenheimer-Stix, John Dunn and Ralf Krüger "Rubber, 4. Emulsion Rub ...

. Prior to the introduction of the Bodok seal, the traditional fibre washer would frequently splay and cause leakage or adhere to the regulator, thus requiring the use of pliers and considerable force to remove it. The Bodok seal consists of a

washer with a peripheral metal reinforcing ring to prevent splaying. The seal is incombustible and resistant to the high pressures imposed upon it by cylinder gases, approximately in a full cylinder. Care must be taken when replacing gas cylinders that the Bodok seal does not stick to the cylinder valve face, and is thus 'lost' when the new cylinder is fitted, preventing a gas tight seal. Bodok seals are also used in emergency oxygen kits used in first aid for underwater diving, but diving regulators used for scuba cylinders generally use a conventional

o-ring An O-ring, also known as a packing or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross section (geometry), cross-section, designed to be seated in a groove and compressed during assembl ...

seal with either a DIN 477 or CGA 850 yoke connector.

Limitations

It is possible to bypass the pin-index system if the pins are removed, damaged or corroded, if extra washers are used, or on some valves with a short face above the orifice, by inverting the gas cylinder. There is one report of the cylinder being painted the wrong colour leading to error.

Alternative systems

Medical gas cylinders larger than size E (679 liters) are more likely to be fitted with threaded connectors. The connections used for larger cylinders vary widely among jurisdictions. One such system are the American CGA fittings. In Europe there are

British Standard British Standards (BS) are the standards produced by the BSI Group which is incorporated under a royal charter and which is formally designated as the national standards body (NSB) for the UK. The BSI Group produces British Standards under th ...

(BS),

German Standard German(s) may refer to: * Germany, the country of the Germans and German things **Germania (Roman era) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizenship in Germany, see also Ger ...

(DIN) and French (AFNOR) connections, and Japan has the Japanese Standard (JIS).

Blanking Plugs

Blanking plugs (dummy cylinder heads) can be inserted into empty yokes to ensure that there is no leak out of the yoke when not in use.

References

{{reflist, refs= {{cite web, url=https://www.concoa.com/cgachart.html, title=CGA Fitting Reference , website=www.concoa.com, last=staff, accessdate=12 August 2017 {{cite web, url=http://www.crcresources.com/files/medical_gas_safety.pdf , title=Attaching Therapy Equipment: Pin Index Safety System , work=Medical Gases and Safety Systems: CRC 330 , publisher=Cardiorespiratory Care, University of South Alabama , accessdate=12 August 2017 {{cite web, url=https://healthprofessions.udmercy.edu/academics/na/agm/03.htm, title=Supply system: Gases & electricity, work=The Anesthesia Gas Machine, first1=Michael P. , last1=Dosch , first2= Darin , last2=Tharp, publisher=University of Detroit, accessdate=12 August 2017 {{cite journal, journal=Indian Journal of Anaesthesia, title=Anaesthesia gas supply: Gas cylinders, first=Uma , last=Srivastava, year= 2013 , volume=57 , issue =5 , pages = 500–506, doi=10.4103/0019-5049.120147, pmid=24249883, pmc=3821267 , doi-access=free

External links

Bodok seal note
(See "Historical Forum" following "Nerve Plexus" article) Safety equipment Anesthetic equipment