4th August 2022
Gas cylinder safety vs. gas generator safety
You will find gas cylinders in labs all over the world, but we often forget how dangerous these items can be. There is, on average, over 100 accidents reported in the UK by RIDDOR (Reporting of Injuries, Diseases and Dangerous Occurrences Regulations) every year across all industries. RIDDAS reports on fatal and defined non-fatal injuries to workers and members of the public which are reported by employers in Great Britain.
A quarter resulted in a serious explosion or fire and at least 2 resulted in fatalities. In 2021 alone, the UK reported 131 incidents with cylinders which resulted in an injury through direct use of cylinders – these incidents included gas exposure and explosions or fires.
There are many issues that can occur with cylinders, but these can be nullified by using a gas generator. When considering purchasing a cylinder over a gas generator it’s important to consider these safety factors:
Any one of these single cylinder failures poses a health risk.
- Internal stress corrosion cracking the cylinder
- Cylinders can fail if over-pressurized or weakened by the application of heat
- Cylinders are structurally weakened by the application of any heat source
- Cylinders may ‘rocket’ if the regulator and valve assembly is damaged
- Cylinders protected by pressure relief valves, fusible plugs or bursting discs may not work correctly in a fire, or if they are damaged
- Accidental application of compressed gas into the eyes or an open wound
- Damage during transportation, though the cylinder may have passed inspection on leaving the supplier the same rigorous test is not applied on delivery.
- Heavy stamp markings contribute to the micro fragmentation of the cylinder during failure
On the other hand, consecutive failures are required to cause a failure in an H2 generator
- Hydrogen vent blockage – causing H2 build-up in the generator
- Oxygen vent blockage – causing O2 build-up in the generator
- Hydrogen exhaust blockage – causing a build-up of H2 in the PSA dryer (Pressure Swing Adsorption Dryer)
- Proportional valve failure – preventing delivery of H2 from the generator
- Pressure sensor failure – 3 sensors would need to fail simultaneously
- Valve failure – 4 valves would need to fail simultaneously
- Non-return valve failure – 3 non-return valves would need to fail
- Separation tank blockage – Hydrogen forced into the internal water tank
While this is not an exhaustive list of risks associated with gas cylinders, you can find even more safety concerns in this article by Richard Palluzi.
Though many gas generators carry similar safety measures, an H2 generator has increased safety features as it produces a flammable gas.
Most common injuries from cylinders
The most common injury from the use of compressed air is to the eyes. Compressed air is used in most industries to blow off and clean workplaces of dirt and debris. A leading cause of eye injury is chips and particles bouncing back towards the operator when blowing off or working.
The noise from compressed air can cause damage to the ears. Compressed air exhaust noise can be loud when used for blow-off or cooling. Blowing with compressed air can result in elevated noise levels that can be harmful to both the operator as well as surrounding people. Both short and repeated blowing operations can be harmful and result in hearing damage and tinnitus.
The skin and body
As well as the burning/freezing hazard with some compressed cylinders, skin and body damage can also occur from flying debris when using compressed gas air for blow-off or cooling machinery.
A very serious situation occurs when compressed gas enters the bloodstream – an aeroembolism. This can happen if the operator accidentally blows compressed gas on themselves during the cleaning or installation process. If the pressure becomes too great or the compressed air is blown directly against the body, the compressed air can get underneath the skin and into the bloodstream.
How can you check your cylinder is safe?
Here are some tests that you can do to make sure your cylinder is safe.
Check to make sure that residual pressure remains in the cylinder.
A weight check is designed to detect very low levels of contamination. However, cylinder tare weights are normally only specified at 100 grams and it has been shown that as little as 5 grams of water could be enough to destroy a gas cylinder.
Moisture detection, though there are limitations in its use, may be appropriate for online monitoring of the gas going into the cylinder but it is an unreliable method of detecting moisture already present inside the cylinder from either rainwater or liquid backfeed.
Where gas generators can be proven to be clear of contamination (as the gas is produced on site), cylinders cannot.
To be sure there is no internal contamination, safe removal of the cylinder valve would be required. This must then be replaced using the correct tools and torque settings before being refilled.
By-products of this procedure include increased wear on the valve threads and increases in the risk of moisture ingress while the valve is removed. This method also relies on the person carrying out the inspection being capable of detecting small quantities of moisture, so they must have good eyesight and a good source of lighting for the inside of the cylinder.
Where contamination is found, the cylinder should be sent to an approved gas cylinder inspection body for a thorough examination. It should be noted that if valves are removed and refitted by the filler then the correct torque must be applied when tightening the valve back into the cylinder.
Cylinders, on average, should have a contamination test roughly every 5 years by a recognized inspection body.
The list of risks associated with the use of gas cylinders is a long one and these risks are not unfounded, given the number of incidents reported annually in Great Britain alone. It’s safe to assume that, if these incidents are happening in one region, they are happening in other parts of the world.
The easiest way to ensure you have a safe environment is to stop the use of cylinders altogether and invest in the safer, more reliable alternative – an on-site gas generator.