COS/Advanced/TBT-COS-040

Working with Nitrogen

COSHH & Hazardous Substances › Advanced › Working with Nitrogen

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Nitrogen is an odourless, colourless gas used on construction sites for purging, inerting, and pressure testing.
Nitrogen displaces oxygen in enclosed spaces — air normally contains 21% oxygen, below 18% causes impairment.
At 6% oxygen concentration, unconsciousness occurs within seconds and death follows within minutes.
The Confined Spaces Regulations 1997 apply wherever nitrogen could accumulate and reduce oxygen levels.
Nitrogen is supplied in high-pressure cylinders at up to 200 bar or in bulk liquid dewars at cryogenic temperatures.
Liquid nitrogen boils at minus 196°C — contact with skin causes instant cryogenic burns and frostbite.
Nitrogen gas leaks are impossible to detect by smell, taste, or sight without oxygen monitoring equipment.
Common construction uses include pipe purging before welding, leak testing, and chemical plant inerting.
COSHH 2002 and DSEAR 2002 both apply to activities involving nitrogen use on construction sites.
Multiple fatalities have occurred in the UK from workers entering nitrogen-purged spaces without monitoring.

Asphyxiation risk	Nitrogen silently displaces oxygen — workers collapse without warning and die within minutes in enriched atmospheres.
Invisible killer	You cannot see, smell, or taste nitrogen — only a calibrated oxygen monitor can detect dangerous concentrations.
Cryogenic burns	Liquid nitrogen at minus 196°C causes instant tissue destruction on contact with skin or eyes.

Don't

Use a calibrated oxygen monitor when working near any nitrogen supply or purged system.
Ventilate enclosed areas thoroughly before entry where nitrogen has been or is being used.
Ensure nitrogen cylinders are stored upright, secured, and away from heat sources.
Follow the confined space entry procedure for any area where nitrogen could accumulate.
Wear cryogenic gloves and face shield when handling liquid nitrogen or dewars.
Label all pipework and valves carrying nitrogen clearly with the correct hazard signs.
Brief all workers in the area before starting any nitrogen purging or testing operation.
Ensure emergency rescue equipment is available before nitrogen operations commence.
Monitor oxygen levels continuously during and after nitrogen purging activities.
Close nitrogen cylinder valves when not in active use and cap regulators securely.

DON'T enter any space that has been nitrogen-purged without continuous oxygen monitoring.
DON'T assume a well-ventilated area is safe — nitrogen settles in low points and pits.
DON'T touch liquid nitrogen, frosted pipes, or cryogenic equipment with bare skin.
DON'T store nitrogen cylinders in confined spaces, basements, or unventilated rooms.
DON'T use nitrogen for tasks where compressed air would be equally effective and safer.
DON'T rely on your senses to detect low oxygen — unconsciousness occurs without warning.
DON'T allow untrained workers near nitrogen operations without a specific safety briefing.
DON'T transport nitrogen cylinders lying flat in enclosed vehicle compartments.
DON'T disconnect nitrogen supply hoses while the system is still pressurised.
DON'T open nitrogen valves rapidly — sudden pressure release can damage equipment.

See also: Confined Space Awareness | Atmospheric Monitoring and Gas Detection

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