Nitrogen Safety

Nitrogen is a  colorless, non toxic, odorless gas and practically inert. It does not support aerobic life or combustion. The pharmaceutical industry utilise nitrogen as an inerting gas to purge, blanket and sweep vessels and equipment containing flammable liquids. It is cheap and easy to make by liquefying the air then fractionally distilling this liquid to obtain 100% nitrogen. Often pharmaceutical facilities have local liquid nitrogen storage tanks on site with distribution pipework to user points. These are often rented from gas supply companies like Air Products or BOC.

Nitrogen is the largest constituent of the air in our atmosphere at sea level and up to 16000m altitude. The air consists of the following proportions of gases: 78% is nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide, 0.07% mixture of hydrogen, helium, krypton, xenon. All are odorless, tasteless, colorless. This ratio does not change as you gain altitude, however the concentrations drop.

At 5000m where there is approximately ½ atmospheric pressure at sea level. The amount of available oxygen falls to about half that available at sea level. This is about the height of Everest base camp and requires the body to slowly acclimatise to function in the the thin air conditions. Fly up in a helicopter from sea level with no acclimatisation and jump out, you will feel dizzy and unwell, your breathing rate will be high, panting, as your lungs struggle to get enough oxygen into your blood. This happens because carbon dioxide builds up in your blood triggering your physiology to breathe more. Carbon dioxide, in the blood, is the bodies main urge to breathe mechanism, not lack of oxygen in the blood.

Height Diagram

Unlike a climber at extreme altitude, If a free diver hyperventilates (takes several very deep rapid breaths) before diving. This reduces the feeling of need to breathe so the diver can spend longer underwater. This is because the, misguided, diver is flushing out the carbon dioxide from their blood, but adding very little oxygen. The lack of oxygen in the brain causes a grey out of faint underwater with very serious consequences for the diver. The rule is never hyperventilate before a breath hold dive just breath normally before holding your breath to dive.

Working in pharmaceutical facilities it is important to understand the hazards that nitrogen presents. Its is known as the silent killer. Like the hyperventilating breath holding diver.  If you happen to walk into a clean room or enter a confined space and breathe an oxygen depleted atmosphere. The brain trigger does not happen, you feel fine, however you will suddenly still faint, without warning, due to lack of oxygen to your brain. Do not think “I will feel funny and be able to escape”.  Breathing an oxygen depleted atmosphere due to increased nitrogen gives very little or no warning. This is why it is so important we take special precautions with nitrogen in our facilities.

Table of oxygen concentration Effects of Oxygen Deficiency on Humans:-

20.9 – 19.5% Normal (19.5 Legal Minimum Concentration OSHA regulations)

19.5 -19% Unnoticable Physiological Effects

19-15% Increased Pulse and Breathing rate Impaired thinking and coordination

15-12% Abnormal Fatigue emotional Upset poor judgement

12-10% Very poor Coordination and judgement,Giddiness, Blue Lips.

10-8% Impaired reparation Nausea and Vomiting, Unconsciousness

8-6% 8 mins 100% fatalities 6 mins 50% fatalities 4-5 mins recovery expected

<6%Coma in 40 seconds convulsions breathing stops death

Sources Compressed Gas Association 2001 and Air Products, Use Nitrogen Safely

Nitrogen is such a painless way to die it is being considered for Euthanasia and capital punishment. As pharmaceutical plant designers and operators we have a duty to minimise the risks anywhere nitrogen or inert gases are used in our facilities.

Confined spaces are considered hazardous and special precautions are routinely taken. Vessel entry being an example where entry is not routine. Routine confined space entry to Sealed small Clean Rooms require special design features good practice requires having additional oxygen analyser alarm systems to sound the alarm via lights and sounders and annunciators in control rooms.

Fig 2 Example of Oxygen Meter set to alarm below 19.5% a Oxygen Ntron OxyTX

These systems also act to shut actuated valves on the nitrogen supply to the room and switch HVAC to 100% fresh air and ramp to give maximum air changes.

Restriction orifices are often required to limit the nitrogen flow by choking the flow in the event of a large leak. The RO must be sized to ensure any leak will not give a general asphyxiating atmosphere. This is usually by assuming an allowable leak rate of 1/12 of the room air change flow (4-6 changes per hour or higher for clean rooms) which with air at 20.5 % oxygen would drop to 19% not ideal but gives an overall control. 19.5% is the normal working safe low limit in most guides.

Remember all information in this article and information sources is for engineers information only. You must check the facts when applying it in the context of your own projects.

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Sources used for this article and further reading

Chemical Safety and Hazard Investigation Board

Safety Bulletin Hazards of Nitrogen Asphyxiation No 2003-10-B Jun 2003

http://www.csb.gov/assets/1/19/SB-Nitrogen-6-11-031.pdf

Air Products

Use Nitrogen Safely

Paul Yanisko & Dennis Croll

http://www.airproducts.com/microsite/Nitrogen_Blanketing/PDFs/en-use-nitrogen-safely-312-12-023.pdf

Wikipedia

http://en.wikipedia.org/wiki/Shallow_water_blackout

http://en.wikipedia.org/wiki/Inert_gas_asphyxiation

INERT GASES (Death by Asphyxia, Most Humane)

Jan L. Lary

HSE

Confined Spaces A brief Guide to Working Safely

http://www.hse.gov.uk/pubns/indg258.htm

bp Booklet Ten Hazards of Nitrogen and Catalyst Handling

http://www.logisticsmatters.info/Tank%20entry%20and%20Risks%20of%20Inert%20Gas/Hazards.of.Nitrogen.and.Catalyst.Handling.pdf

Chilworth Technology, Inc

Preventing Explosion Hazards- Inert Gas Blanketing

(First Published in Solids Handling, May/June 1994)

http://www.chilworth.com/wp-content/uploads/2012/10/PreventingExplosionHazards-InertGasBlanketing.pdf

 

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