Coal Inspectorate | Alert | No.410 V 1 | 03 June 2022
Use of liquid nitrogen in the mining industry
On Tuesday 17th May, a worker received serious cryogenic burns after immersing their hands in a container of liquid nitrogen whilst trying to shrink a brass bush for inserting into an excavator boom arm. Whilst this incident did not occur on a mine site, this type of work may be conducted on mine sites, and in many cases may be done by contractors. Regardless of who conducts the work, the Mine Safety and Health Management System must manage the risks associated with the safe use and handling of liquid nitrogen or similar substances, if it is used at the mine.
How did it happen?
Work Health and Safety Queensland inspectors reported that the worker was not wearing the correct personal protective equipment for the task. Further details related to the incident are not available at this time
Liquid nitrogen is one of the cryogenic liquids commonly used in the mining industry. As “cryogenic” means related to very low temperature, it is an extremely cold material. Liquid nitrogen has a boiling point of negative – 195.8 degrees centigrade and can expand to a very large volume of gas.
The vapor of liquid nitrogen can rapidly freeze skin tissue and eye fluid, resulting in cold burns, frostbite, and permanent hand and eye damage, even by brief exposure.
Liquid nitrogen expands 695 times in volume when it vaporises and has no warning properties such as odour or colour. Hence, if sufficient liquid nitrogen is vaporised to reduce the oxygen percentage to below 19.5%, there is a risk of oxygen deficiency which may cause unconsciousness. Death may result if oxygen deficiency is extreme. To prevent asphyxiation hazards, handlers must make sure that the work area is well ventilated.
Without adequate venting or pressure-relief devices on the containers, enormous pressures can build upon evaporation. Users must make sure that liquid nitrogen is never contained in a closed system. Use a pressure relief vessel or a venting lid to protect against pressure build-up.
Handling Safety Practices
- Liquid nitrogen should be handled in well-ventilated areas.
- Handle the liquid slowly to minimize boiling and splashing.
- Use tongs to withdraw objects immersed in liquid nitrogen - Boiling and splashing always occur when charging or filling a warm container with liquid nitrogen or when inserting objects into the liquid.
- Use only approved containers. Impact resistant containers that can withstand the extremely low temperatures should be used. Materials such as carbon steel, plastic and rubber become brittle at these temperatures.
- Only store liquid nitrogen in containers with loose fitting lids (Never seal liquid nitrogen in a container). A tightly sealed container will build up pressure as the liquid boils and may explode after a short time.
- Never touch non-insulated vessels containing liquid nitrogen. Flesh will stick to extremely cold materials. Even non-metallic materials are dangerous to touch at low temperatures.
- Never tamper or modify safety devices such as the cylinder valve or regulator of the tank.
- Liquid nitrogen should only be stored in well-ventilated areas (do not store in a confined space).
- Do not store liquid nitrogen for long periods in an uncovered container.
- Cylinders should not be filled to more than 80% of capacity, since expansion of gases during warming may cause excessive pressure build-up.
Eye / Face Protection
- Suitably rated full face shield over safety glasses or chemical splash goggles are recommended during transfer and handling of liquid nitrogen to minimise injuries associated with splash or explosion.
- Suitably rated, loose-fitting thermal insulated or leather gloves, aprons, long sleeve shirts, and trousers without cuffs should be worn while handling liquid nitrogen. Safety shoes are also recommended while handling containers. Gloves should be loose-fitting, so they are able to be quickly removed if liquid nitrogen is spilled on them. Insulated gloves are not made to permit the hands to be put into liquid nitrogen. They typically only provide short-term protection from accidental contact with the liquid.
Site Senior Executives (SSEs) must:
Identify if liquid nitrogen or other cryogenic substances are used or likely to be used on the mine site. Consideration should be given to the use of alternative engineering solutions.
Where liquid nitrogen or other cryogenic substances are to be used on site:
- ensure risk assessed procedures are developed, implemented and communicated. This should include the provision of appropriate tools (tongs, baskets, lifting jigs), suitably rated PPE (gloves, apron, double eye protection) and task specific procedures.
- provide site-specific training in the use of liquid nitrogen or other cryogenic substances. Records of training shall be maintained.
- ensure site procedures for the safe use of liquid nitrogen or similar cryogenic substances are implemented and followed.
- understand and comply with site procedures for the safe use of liquid nitrogen or similar cryogenic substances.
Investigations are ongoing and further information may be published as it becomes available. The information in this publication is what is known at the time of writing.
We issue Safety Notices to draw attention to the occurrence of a serious incident, raise awareness of risks, and prompt assessment of your existing controls.
Contact: Anthony Logan, Senior Inspector of Mines , +61 7 3199 8013 QldMinesInspectorate@rshq.qld.gov.au
Issued by Resources Safety & Health Queensland
Placement: Place this announcement on noticeboards and ensure all relevant people in your organisation receive a copy, understand the content, findings and recommendations as applicable to their operation. SSEs should validate that recommendations have been implemented.