How dangerous is a calibration gas cylinder? What to be aware of and tips for handling.
Calibration gas cylinders are considered dangerous goods. But, how dangerous are they, really? After all, most gas calibration gases are classified as “non-toxic, non-flammable” gases.
Aside from the obvious hazards associated with flammable and toxic gases, all compressed gas cylinders have associated hazards which the user should be aware of.
Cylinder contents.
Firstly, it is important to understand the difference in UN DG classification and recognising dangers when using and handling cylinders.
Even cylinders whose contents are classified as non-toxic and non-flammable can be very hazardous to health.
As we noted in a previous article, chlorine up to and below 2000ppm in nitrogen is considered non-toxic and non-flammable. But, as all occupational health and safety professionals would know, concentrations of 2000ppm chlorine is very toxic (TWA: 1 ppm STEL: 0.5ppm). Even though this article won’t get into the details of how transport classifications are determined, and though they are based primarily on risk to human health, they are designed to direct action in emergency situations rather than provide guidance for safe usage. Those interested can read more here.
Always read the SDS! Relying on the transport classification is not sufficient. Gases can vary greatly in danger, even if they are within the same UN classification.
Explosive decompression.
Calibration gas cylinders can be pressurised between about 3 to 300 BAR. On the outside, a cylinder filled to 3 BAR will appear the same as one filled to 300 BAR. A cylinder filled to a higher fill pressure represents a greater danger if it is punctured, cracked, or otherwise damaged.
Generally, it is impossible for a cylinder to undergo explosive decompression without having suffered some sort of external damage. It is true that certain cylinder types filled with certain components can be structurally compromised through chemical reactions over long periods of time. This isn’t really a concern because refillable cylinders must undergo hydrostatic pressure testing every 10 years and non-refillable cylinders are single use only. Signs of such potential failures would be evident long before structural failures occurred.
Cylinders which undergo rapid or violent decompression can become missiles. It is important not to underestimate the potential damage a venting cylinder can cause. Under the right conditions cylinders can pass through walls or cause other significant damage. This was demonstrated on the TV show “Mythbusters:” https://youtu.be/C4kb-8CjVYg
Take care to secure your cylinders in place using mounts. Never leave cylinders in a position where they can be bumped or knocked over. Avoid placing cylinders in areas where there is potential for the valve to contact another object if it were to fall. Be careful when moving cylinders. When storing cylinders, ensure the protective valve cap is installed.
Low temperatures.
Another effect of rapid decompression is extremely cold temperatures. Gases cool when they decompress and temperatures can reach damaging levels if the decompression is violent enough. If the cylinder comes into contact with skin, cold burns can result.
If you have a cylinder which is quickly decompressing do not attempt to touch the cylinder until sufficient time has passed to allow the cylinder to come back to ambient temperature.
Weight of the cylinders.
Some cylinders are upwards of 70Kg with a relatively small base to stand on. If a cylinder topples do not attempt to catch it or steady it as serious injury may occur.
If I leave my cylinder in the sun, will it explode?
Although generally it isn’t a good idea to leave your gas cylinders in direct sunlight, heat from sunlight alone will not cause your cylinder to explode. Calibration gas cylinders typically have working pressures at about half the burst pressure rating. To reach the burst pressure the cylinder would need to be exposed to extreme temperatures, such as in a fire.
Some cylinders are equipped with a pressure relief device. This device is designed to vent cylinder contents before the cylinder reaches burst pressure. It is conceivable that naturally occurring heat (such as strong sunlight on a hot day) could cause venting of cylinder contents.
If you are unsure if your cylinder has a pressure relief device, contact CAC Gas.
