- Hazards & Risks associated with Compressed Gas Cylinders
- Training
- Pre-Use Cylinder Checks
- Regulator Inspection
- Leak Testing
- Manual Handling
- Oxygen Monitoring
- Other Information
(Last updated 7/5/13)
1. Hazards & Risks associated with Compressed Gas Cylinders
Most accidents with containers of compressed gases occur in their handling due to their mass, shape and size. Full gas cylinders can weigh more than 100 kg for compressed gases or 150 kg for liquefied gases. When moving them or working with them they can present risk of crush injuries to hands, fingers and feet and manual handling type injuries to back and upper/lower limbs. Such injuries can be permanently debilitating.
The force exerted by gas decompressing from high pressures is tremendous. Uncontrolled release of gas can present risk of serious injury from the gas itself and/or flying projectiles, and may cause damage to equipment. At worst, it could turn the cylinder itself into a projectile. Such uncontrolled release can occur due to inadvertent opening or shearing of the container valve, or use of a faulty, unsuitable or incorrectly fitted regulator. Even with a correctly fitted regulatory, unsuitable/faulty/incorrectly fitted apparatus downstream from the regulator may leak hazardous gas or even explode under pressure and again possibly creating flying projectiles and damaging equipment.
Containers exposed to high levels of radiant heat, e.g. from a local heat source such as a nearby fire or boiler, may explode due to over-pressurisation.
Another problem can occur when the contents of any large gas cylinder — other than an air cylinder — vent rapidly, even if the cylinder is restrained. A sudden, large volume release of unbreathable gas in the laboratory will reduce the level of oxygen in the air dramatically and present a real risk of asphyxiation.
Other risks associated with the gas itself depend upon its intrinsic hazardous properties. The supplier's Safety Data Sheets will give this information. See below for data sheets for most gasses used in SLS. Groups using special gas mixtures must ask the supplier for the relevant data sheet.
Personnel whose job entails the handling and use of gas cylinders must receive specific training at the earliest opportunity. If you fall into this category and have not previously attended a relevant training course, inform SLS H&S immediately. SLS and/or Safety Services will either deliver in-house training or, if necessary, arrange for an external, specialist training company to deliver the required training as soon as possible.
- Ensure the cylinder is properly secured to prevent movement. Cylinders must never be left unsecured.
- Check that the cylinder is clearly labeled and that the cylinder colour corresponds with the label. Check the pressure rating of the cylinder. Never use a cylinder unless it can be clearly identified. A cylinder without a label should not be used. Return it to Stores and they will send it back to the supplier.
Example label
- If the cylinder is new the valve should be capped. If the cap is missing do not accept the cylinder. Inform Stores and they will return it to the supplier.
- Once the cap is removed, check that the valve is undamaged and free from dirt, moisture, oil, grease, PTFE tape and any other debris. If the valve is damaged or contaminated with grease, oil or PTFE tape that cannot be removed, do not use the cylinder. Return it to Stores and explain what the problem is. Stores will return it to the supplier. Moisture can be absorbed with a lint free cloth. Dirt and and other debris can be blown out using a clean, dry, low pressure air supply.
Pressure regulators used in conjunction with compressed gas cylinders must be checked before each use and formally inspected every year. Lab Managers are expected to ensure this is done in their area and should keep an inventory of all regulators to be inspected*. The Regulator Inspection Checklist should be used as a guide for before-use checks and a hardcopy must be completed during the annual inspection. See the Guidance Sheet for advice on how to complete the Checklist. (If you are not overly familiar with the terminology, click here for a picture of a regulator with all the parts referred to in the Checklist clearly labelled.) Any negative responses must be addressed. Completed Checklists should be kept on file until the regulator is disposed of. Note: if a regulator is not already stamped with a unique serial number, label it with a unique identifier.
*Note: fixed, i.e. plumbed in, gas manifold systems and tested/inspected annually to a written scheme of examination by external, specialist engineers. SLS H&S keep an inventory of these systems and records of the annual inspection/test.
Manufacturers, suppliers and independent training agencies all recommend that regulators are replaced after 5 years. Newer regulators have the expiry date stamped on the regulator body. This fact sheet explains how to decipher date stamps.
If a regulator is defective replace it immediately.
Keep regulators clean, especially oxygen regulators, they must be kept scrupulously clean.
Leaks may develop in any part of a gas system, but particularly at joints. It is important that all elements of a gas system are checked for leaks after initial assembly and corrective action taken before first use. The system should be leak tested before each subsequent use. It is especially important to leak test the system each time a new cylinder is attached to the equipment. End users are best placed to leak test their own gas systems.
It is important to ensure the leak test solution is compatible with the gas used and the materials used in the equipment construction. Incompatible solutions can lead to stress corrosion cracking of the cylinder valve. Also solutions that contain fatty acids or that have an oil base can ignite if they come in contact with oxygen. For this reason soapy water or washing up liquid must not be used. Swagelok SNOOP Liquid Leak Detector was recommended by an external trainer and is available from Sigma.
Performing a Leak Test
- Ensure the leak test solution is compatible with any material it may come into contact with.
-
Apply
the leak test solution to joints and any potential leakage points, such
as at the point of connection
of the cylinder valve with the regulator. - Apply the solution slowly and carefully to avoid frothing.
- You should never apply leak test solution into a cylinder valve outlet. Leakage around the spindle of the cylinder valve will be revealed by hissing. Do not use the cylinder and do not attempt to repair the leak. Move the cylinder to an area where the leak can disperse safely, label it and advise Stores.
- If bubbles start and continue to form, the system should be immediately depressurised and the leak corrected. Do not use the equipment until the leak has been rectified.
- After the check has been completed, ensure the area is dry by wiping with a clean, lint-free cloth.
BCGA Technical Information Sheet No.12 gives a summary of the key points relating to safe handling of gas cylinders. Personnel required to manually handle gas cylinders must be fully trained before doing so.
An oxygen monitor may be required in facilities where compressed gasses are in use. If asphyxiant gasses are in use an oxygen depletion monitor may be required; if oxygen gas is in use an oxygen enrichment monitor may be required. In each case, a risk assessment must be carried out to determine whether an oxygen monitor is required and how elaborate the system has to be.
The slide shows listed below give some basic information on oxygen depletion and enrichment and the dangers they pose.