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Nitrogen Safety Awareness Workshop

Heriot Watt University

Edinburgh

22nd and 23rd April 2009

Presented by

Brian King

BOC

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Safety Awareness Workshop

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Module 1 - Properties & hazards of nitrogen

Introduction - Production, supply and common uses

Key physical properties

Safety hazards Oxygen deficiency Intense cold Pressurisation Oxygen enrichment

Safe systems of work and legislation

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But first…….what is a cryogenic liquid?

Simply……..one which is manufactured, transported, stored and often used at a temperature below - 85 degC.

From the Greek

Kryo……….meaning icy cold

» and

Genus……..to produce

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Introduction - Air Separation

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Introduction - Air Separation

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Introduction - Supply Methods

Cylinder Vehicle

Compressed Gases

Tanker

Liquid Product

Air Separation Unit

BOC

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gases

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gases

ArO2N2

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gases

Pipeline

Client

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Introduction - Common Uses of Nitrogen

As a gas for it’s inert properties:-

Removal of oxygen in vessels & processing equipment which contain flammable liquids or vapours. Commonly called purging and blanketing in the Chemicals Industry

“Sparging”of fluids (e.g. water & edible oils) to remove oxygen

Gas packing of foodstuffs to remove oxygen and extend shelf-life

Humane slaughter of poultry

Furnace atmospheres e.g nitriding to improve surface hardness of gears etc

As a liquid for it’s cryogenic properties:-

Food freezing & chilling

Cooling chemical reactions & condensation of VOCs from chemical vent-streams

Low temperature grinding (e.g rubber, fats & spices)

“De-flashing” moulded rubber components

Low temperature testing of electronic equipment

Shrink fitting & pipe freezing

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Gases in air (by volume %)

0.9320.95

78.08

Nitrogen Oxygen Argon Other

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Important nitrogen characteristics

Odourless

Tasteless

Colourless

Non toxic

Inert (non reactive)

Non flammable

Asphyxiant (does not support life)

Gives no warning of presence

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Important properties of nitrogen

Temperature

Liquid nitrogen boils at -196 degC (at atmospheric pressure)

Expansion ratio

One volume of liquid creates 680 volumes of gas at room temperature

Density

Gaseous nitrogen is slightly lighter than air, however cold nitrogen vapour is much heavier and will fall rapidly to low level

*

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Safety Hazards

Due to :-

Oxygen deficiency

Intense cold

Pressurisation

Oxygen enrichment

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1. Oxygen Deficiency

The dilution or displacement of air with nitrogen will reduce the oxygen level and may cause asphyxia

Less than 20% oxygen is not recommended in the workplace Less than 18% can be potentially dangerous In severely O2 deficient atmospheres, only two breaths may lead to

unconsciousness and death

Caused by Nitrogen discharge into confined spaces

» Spillage from portable open top vessels (dewars) or other containers

» Pipework leaks / disconnected hoses / valves inadvertently left open

» Process vents not routed to a safe discharge area

Aggravated by poor ventilation

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Symptoms of Asphyxia

Symptoms may include:-

Rapid breathing/shortness of breath Rapid fatigue Nausea Vomiting Collapse or inability to move Unusual behaviour

The person suffering from asphyxia will be unaware of the symptoms and may even feel euphoric!

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Oxygen Deficiency - Precautions

Where appropriate, consider permanently installed oxygen detection equipment, which has:-

Mains electrical supply with back-up batteries

Visual/audible alarms both inside & outside working area, typically set to operate at 19% oxygen concentration

Sufficient sensors positioned close to where a leak may occur

Possibly interlocked to a nitrogen isolation valve and forced extraction system

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Oxygen Deficiency - Precautions

Avoid working in confined spaces if possible. Adopt appropriate procedures ifconfined space working is unavoidable

Consider personal O2 monitors (especially for confined space entry)

Note that there is no specific legislation governing gas detection equipment, however it should be considered during risk assessments

Ensure good ventilation

Post warning signs

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Permanently installed oxygen detection system

Courtesy of Draeger Safety Ltd

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Personal Oxygen Monitor

Courtesy of Draeger Safety Ltd

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Asphyxiant - Warning Sign

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Oxygen Deficiency - Rescue and Treatment

Raise the alarm and call for medical assistance

Isolate the nitrogen supply if safe to do so

Never enter a potentially oxygen deficient environment unless you have checked the atmosphere is breathable and are preferably wearing a breathing apparatus set. Breathing apparatus should only be used by a trained person. Don’t rush in and be the second victim!

Ideally use a life line and “buddy” system in conjunction with the breathing apparatus set.

If victim is not breathing, use artificial respiration

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2. Intense Cold - Hazards

Cold burns, frostbite and hypothermia

Vapour clouds

Brittle fracture of materials of construction

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Cold Burns

Caused by

direct contact with cryogenic liquid gases, or more usually cold surfaces (e.g. un-insulated pipelines, hoses or cold equipment).

Results in

skin sticking to cold surfaces frozen tissue & localised damage to cell structure waxy pallid yellow appearance of affected area pain and potentially shock during thawing

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Intense Cold - Hypothermia & Frostbite

Hypothermia is caused by prolonged exposure to cold environments (less than 10 degC). It results in slowed physical & mental responses, irritability, speech & vision difficulties, shivers & cramps and can be fatal

Frostbite is caused by prolonged exposure of unprotected skin to very cold atmospheres (e.g. low temperature vapour). It results in similar effects to a cold burn, but over a greater area

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Intense Cold - Treatment

Raise the alarm and call for medical assistance

Isolate the liquid nitrogen supply if appropriate (e.g. flesh stuck toun-insulated pipeline)

Flush cold burns & frost-bitten areas with copious amounts of tepid water (42-45degC). Never apply dry heat as a hot burn may result on top of the cold burn

Loosen any tight clothing which may restrict blood supply to the affected area. Dont let patient smoke or drink alcohol as the also restrict blood flow

Keep patient warm and once the affected area has thawed, apply a loose fitting dry sterile dressing

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Intense Cold - Precautions

Use correct PPE Non-absorbent insulated gloves (e.g. leather or PVC) Full face mask preferred. Goggles or safety glasses with side

shields acceptable Safety shoes (particularly important when handling dewars) Wear sleeve cuffs outside gloves and trouser bottoms

outside boots. Ideally wear a non-absorbent apron if decanting liquid.

(Note: Liquid nitrogen penetrates fabrics more easily than water due to it’s lower viscosity)

Warm clothing for low temperature environment working

Insulate cold surfaces

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Use of correct PPE

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Intense Cold - Vapour Clouds

Commonly caused by spillage or release of liquid nitrogen or vessel venting

The resultant vapour cloud will dramatically reduce visibility

Note that cold nitrogen vapour is heavier than ambient air and will collect in pits and trenches, which will then have an oxygen deficient atmosphere

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Intense Cold - Brittle Fracture

Bang !!!!

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Intense Cold - Brittle Fracture

Many materials become brittle at cryogenic temperatures

Metals used for cryogenic service include austenitic stainless steels (grades 306 & 316), copper, aluminium, brass and bronze

Low/medium carbon steels will embrittle at cryogenic temperatures

Polymers are particularly prone to embrittlement. PTFE is the normal choice for use at low temperatures

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3. Pressurisation

Caused by Expansion as a result of liquid to gas phase change, often in

pipeline between closed valves (termed a “liquid lock”)

Can result in Explosive releases (e.g. burst pipelines)

Precautions Correctly rated & sized pressure relief valves, piped to a safe

location

Note that noise levels when venting nitrogen vessels can reach up to 100-120dBa. Therefore wear ear protection if attending a vessel fill

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4. Oxygen enrichment

Un-insulated surfaces cooled by liquid nitrogen can be cold enough to cause atmospheric air to condense on them

Oxygen condenses at a higher temperature (-183 degC) than nitrogen (-196 degC). Therefore condensed liquid air has a higher oxygen content (about 40%) than normal atmospheric air (20.8%)

If this liquid drips onto a combustible surface, such as fabric, paper, grease, asphalt etc. an explosion or fire could result if there is also a source of ignition

Always ensure cryogenic pipelines and equipment is insulated

Report any pipeline “leaks”, even if slight. A fractured nitrogen line will generally result in a pressurised leak. Condensed liquid air will drip.

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Case Study - Oxygen Enrichment

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Safe Systems of Work

When working on nitrogen systems, extreme care is needed to ensure a safe system of work is in place before work commences

A “permit to work” system is often used. Also, other recognised safety techniques should be considered, such as :-

Risk assessments Method statements Gas analysis (e.g. oxygen concentration prior to entering

confined spaces) Physical Isolations (e.g spool piece inserted in to pipeline before

entering vessel) Safety training & instruction

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Legislation applicable to nitrogen users

In addition to general Acts & Regulations (e.g. Health & Safety at Work Act, Management of Health & Safety at Work Regs, PPE at Work Regs etc), nitrogen users should be aware of the following:-

The Confined Space Regs. - Requires employers to assess risks associated with asphyxiation, fire, explosion, toxic substances etc. in any space which might be partially or wholly confined

The Control of Substances Hazardous to Health Regs (COSHH) - Employers must assess the risks to health from substances used in the workplace. Amended in 2003 to include asphyxiant gases, e.g. nitrogen

The Manual Handling Operations Regs - Requires employers to assess risk related to all manual handling in the workplace. This includes manual handling of dewars by definition.

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Legislation applicable to nitrogen users

The Pressure Systems Safety Regs. - Applies to gas systems operated at a pressure greater than 0.5 barg.

The regulations require that users ensure systems are properly maintained, periodically examined, adequate records of examination kept and are operated within established safe limits

A Written Scheme of Examination (WSE) is required and inspection should be by a competent person.

Note that a WSE is not required if the pressure (bar) x volume (litres) of the system is less than 250

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Summary of Key Points

Nitrogen does not support life and as little as 2 breaths can cause unconsciousness and possible death. Do not enter confined spaces unless following the correct procedures

Cryogenic liquids / vapours and un-insulated pipework/process equipment can be intensely cold. Beware of low temperature vapour in pits and troughs etc. Use appropriate PPE when handling cryogenic liquids and gases

Cryogenic temperatures can cause many common materials to embrittle and fracture

Liquid to gas phase change in a fixed volume will cause pressurisation. Ensure pressure relief measures have been taken where appropriate.

Oxygen rich liquid air can condense on very cold surfaces (e.g. un-insulated liquid nitrogen pipelines). Always report “leaks” whether pressurised or not