Serious burns in liquid nitrogen incident

THE Queensland Mines Inspectorate has issued a warning to coal mine site senior executives to ensure liquid nitrogen is handled safely after an incident in which a worker was badly burned.
Serious burns in liquid nitrogen incident Serious burns in liquid nitrogen incident Serious burns in liquid nitrogen incident Serious burns in liquid nitrogen incident Serious burns in liquid nitrogen incident

Liquid nitrogen is one of the cryogenic liquids commonly used in the mining industry.

On May 17, the worker received serious cryogenic burns after immersing his hands in a container of liquid nitrogen while trying to shrink a brass bush for inserting into an excavator boom arm.

"While 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," the inspectorate said.

"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."

Work Health and Safety Queensland inspectors found the worker was not wearing the correct personal protective equipment for the task.

"Liquid nitrogen is one of the cryogenic liquids commonly used in the mining industry," the inspectorate said.

"As ‘cryogenic' means related to very low temperature, it is an extremely cold material."

Liquid nitrogen has a boiling point of -195.8C and can expand to a very large volume of gas.

The vapour of liquid nitrogen can rapidly freeze skin tissue and eye fluid, resulting in cold burns, frostbite, and permanent hand and eye damage, even with just brief exposure.

Liquid nitrogen expands 695 times in volume when it vaporises and has no warning properties such as odour or colour.

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," the inspectorate said.

"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."

The inspectorate said liquid nitrogen should be handled slowly to minimise boiling and splashing.

"Use tongs to withdraw objects immersed in liquid nitrogen," it said.

"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."

The inspectorate said 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.

A suitably rated full face shield over safety glasses or chemical splash goggles are also recommended during transfer and handling of liquid nitrogen to minimise injuries associated with splash or explosion.