"PISS" redirects here. For other uses, see Piss (disambiguation)
Pin index dimensionsThe 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 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.
Concept
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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.[1]
Pin index configurations
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Pin numbersEach gas cylinder has a pin configuration to fit its respective gas yoke. Refer to the diagram for pin numbers; dimensions are in millimeters.
Pin index yoke connector for medical oxygen filling whip
Detail of pin index yoke connector for medical oxygen
Pin index medical oxygen cylinder valve
International Standards
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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.[citation needed]
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) supported by a metal rim.[1]
Bodok seal
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Bodok SealThe Bodok seal is a specialised washer that ensures a gas-tight seal between the cylinder yoke or regulator of an anaesthetic machine or any medical device requiring a gas supply, and a gas cylinder. 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. 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 neoprene 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 2,000 psi (140 bar) 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 seal with either a DIN 477 or CGA 850 yoke connector.
Limitations
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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.[4][5][6][7]
Alternative systems
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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.[8] In Europe there are British Standard (BS), German Standard (DIN) and French (AFNOR) connections, and Japan has the Japanese Standard (JIS).
Blanking Plugs
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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.[9]
See also
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References
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When using oxygen or any medical gases, it is imperative that patient equipment is connected to the correct medical gas cylinders.
Failure to do so can lead to patients being given the wrong gas, or the right gas at the wrong pressure. Both can have fatal consequences.
Traditionally, the valve outlets used for medical gas cylinders in the UK and Ireland have been shared across a number of different gas types. One way of minimising this risk is to ensure that different standards and outlets are used for different medical gases.
As part of our work on Technical Sub Committee 7 – Medical Gases, for the British Compressed Gases Association (BCGA), our team was involved in the creation of Technical Information Sheet 21: Medical Gases – BCGA Policy on Valve Outlets.
You can read BCGA TIS 21 in full here.
The guidance document provides in depth information on the different standards that can be used for medical gas cylinders to minimise risk and improve patient safety.
It covers:
There are three main standards that can be used in the UK and Ireland when specifying the cylinder valve outlets for medical gas cylinders. These are:
This refers to pin-index yoke type connections, typically used on cylinders up to 5L in capacity. It provides up to 16 different outlets for a range of different medical gases.
This standard includes a number of connections for different medical gases and mixtures. It is used primarily for the filling connection for valves with internal pressure regulators, but can also be used on medical gas cylinders with non-pressure related outlets to provide a different valve connection for higher pressure cylinders.
This standard is used to specify all other cylinder valve outlets. Although it provides unique, product specific valve outlets for nitrous oxide and carbon dioxide, it specifies the same 5/8” BSP bullnose valve outlet for use in a range of different medical and industrial gases and mixtures.
To minimise the risk of using the wrong cylinder package – a programme of change has been implemented to convert all non-oxygen cylinders to gas specific outlets.
As part of the process, medical oxygen cylinders will be the only medical gas cylinders fitted with the same BS 341 Part 3 [1] 5/8” BSP bullnose valve outlet. All other medical gas cylinders fitted with bullnose valves will be converted to product specific valves, or will have the bullnose valves replaced with valves with integrated pressure regulators.
This process will be supported by other changes to medical gas cylinders, including the ongoing programme to change the body colour code to white. Take a look at our previous blog on medical colour coding here.
The Technical information sheet includes full details on the steps suppliers are taking, how this process will work, and how these changes should be communicated to customers.
AMS Composite Cylinders supplies state of the art, lightweight aluminium and carbon composite gas cylinders for a wide range of healthcare, homecare, breathing gas and medical gas applications.
We supply clients across the UK, Europe, the Middle East and Latin America, providing industry leading quality, reliable service and short lead times.
Producing cylinders to a wide range of recognised global standards, we hold accreditations in all major markets worldwide. We manufacture to ISO and EN standards (including ISO-11119-2, ISO 11119-1, EN 12245, EN 12257, ISO 7666, ISO 11118 and EN12245) and to the requirements of UN PED/TPED, DOT (USA) and TC (Canada).
For additional information AMS Composite Cylinders, our medical gas cylinders and our accreditations, please contact us today.