Most commercially distributed gases are colorless and odorless. In other words, the gases, when outside the tank, cannot readily be identified. Users and distributors, thus, depend on accurate labeling of tanks to identify the contents. However, because the small risk of a labeling error could result in dramatically harmful consequences, an additional safeguard is utilized.
The threads of the tank fittings are designed to match the threads for a particular regulator. This measure is intended to prevent a user from connecting the wrong kind of gas to an existing gas outlet. In 1999, the Compressed Gas Association (CGA) designated codes to identify threads in a fitting. These codes are stamped, generally, on the regulator just above the threads of the cylinder connection and also on the cylinder valve. Without these stamped codes, the identity of threads would be lost once the threads are forced in a mismatching connection. The CGA recognized the need for these stamped numbers as a result of incidents of valve ejection from cylinders with mismatched threads to these valves.
One example of a thread variation is the reverse threading used for flammable gases. This acts as an additional safeguard. Flammable gas fittings cannot be connected to non-flammable regulators because they require counterclockwise turning for connection, rather than the conventional clockwise turning.
Below is a list of the CGA valve fitting codes for some typical medical gases followed by an accident report summarizing the deaths of four people caused by connecting a nitrogen tank to an oxygen fitting.
| Gases | CGA Connection # |
| Air | 346 |
| Carbon Dioxide | 320 |
| Cyclopropane | 510 |
| Helium | 580 |
| Nitrogen | 580 |
| Nitrous Oxide | 326 |
| Oxygen | 540 |
Source Credit: Linde Gas LLC, MSDS and Safety, CGA Valve Fittings (http://www.us.lindegas.com/International/Web/LG/US/likelgus30.nsf/DocByAlias/nav_safe_cga) and Compressed Gas Association Technical Bulletin, TB-16, 2004.
“On December 7, 2000, four residents of a nursing home in Bellbrook, Ohio, died and six were injured after being administered industrial nitrogen instead of oxygen. The 84-bed nursing home received a shipment of four portable cryogenic medical gas containers labeled as medical oxygen, but one container also bore an industrial nitrogen label that partially obscured the medical oxygen label. That vessel was filled with industrial nitrogen.
The nursing home was running low on oxygen and sent an employee to connect a new oxygen vessel to the oxygen supply system. The employee mistakenly selected the nitrogen container. Despite recommendations by the Compressed Gas Association, a safety and standards organization for medical and industrial gases, many of the large cryogenic vessels that contain medical gases do not have permanently brazed, or welded, connections or fittings that cannot be removed. The container’s nitrogen-specific gas-use-outlet connection was incompatible with the connector on the facility’s oxygen supply system.
Although the employee initially was unable to connect the container to the oxygen supply system, the fatal connection ultimately was made when an oxygen-specific gas-use-outlet connection from an empty portable cryogenic medical oxygen container was removed and substituted for the nitrogen-specific connection on the industrial nitrogen container. The employee then connected the deadly product to the oxygen supply system. The employee was not properly trained and did not examine the drug label to verify that the product was, indeed, medical oxygen before installing the vessel. Furthermore, the employee did not know that connection incompatibility is a built-in safeguard.”
Source Credit: Bruan, Julie A. Take a Look Before You Hook, Nursing Homes: Long Term Care Management (2006) 55(6):69–71.
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