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Nitrogen Safety Awareness Workshop

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  1. Nitrogen Safety Awareness Workshop Heriot Watt University Edinburgh 22nd and 23rd April 2009 Presented by Brian King BOC 726boc

  2. Safety Awareness Workshop 726boc

  3. 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 726boc

  4. 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 726boc

  5. Introduction - Air Separation 726boc

  6. Introduction - Air Separation 726boc

  7. Client 456 boc gases Pipeline BOC Cylinder Vehicle Tanker 456 boc gases 456 boc gases 456 boc gases N2 O2 Ar Compressed Gases Liquid Product Air Separation Unit Introduction - Supply Methods 726boc

  8. 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 Introduction - Common Uses of Nitrogen 726boc

  9. Gases in air (by volume %) 726boc

  10. Odourless Tasteless Colourless Non toxic Inert (non reactive) Non flammable Asphyxiant (does not support life) Gives no warning of presence Important nitrogen characteristics 726boc

  11. 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 726boc

  12. Safety Hazards • Due to :- • Oxygen deficiency • Intense cold • Pressurisation • Oxygen enrichment 726boc

  13. 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 726boc

  14. 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! 726boc

  15. 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 726boc

  16. 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 726boc

  17. Permanently installed oxygen detection system 726boc Courtesy of Draeger Safety Ltd

  18. Personal Oxygen Monitor 726boc Courtesy of Draeger Safety Ltd

  19. Asphyxiant - Warning Sign 726boc

  20. 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 726boc

  21. 2. Intense Cold - Hazards • Cold burns, frostbite and hypothermia • Vapour clouds • Brittle fracture of materials of construction 726boc

  22. 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 726boc

  23. 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 726boc

  24. 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 726boc

  25. 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 726boc

  26. Use of correct PPE 726boc

  27. 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 726boc

  28. Intense Cold - Brittle Fracture Bang !!!! 726boc

  29. 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 726boc

  30. 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 726boc

  31. 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. 726boc

  32. Case Study - Oxygen Enrichment 726boc

  33. 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 726boc

  34. 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. 726boc

  35. 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 726boc

  36. 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 726boc