For the firefighter and emergency services, understanding oxygen, its properties and those of its compounds is vital. In order for a fire to ‘take hold’ there must be oxygen to feed the flame (reaction). In a fire incident, smoke may displace the oxygen or the fire itself deplete the oxygen, making respiration (breathing) for the responder difficult, leading to unconsciousness and death – if there is no cylinder oxygen via a Breathing Apparatus (BA) set.
When a person has been exposed to heavy smoke in the lungs, oxygen therapy may be required, often with a small percentage addition of helium in the therapy. This is to assist the uptake of oxygen through the lungs with the smaller-sized atomic gas of helium assisting carriage of the oxygen through smoke-damaged lungs, and through the blood stream, often congested with carbon monoxide, and other waste material that is contained in the smoke.
So, let’s look at oxygen, chemically and physically.
Class 2 oxygen (and its compounds within Class 5.1 Oxidising Agents and Class 5.2 Organic Peroxides) is interesting chemically, and this article should help understand a little about it.
It should also be noted that oxygen and its compounds are critical in combatting the emergence of Viruses such as Covid-19, the coronavirus, both in medical therapy, as well as hygiene/cleaning.
Context
There is a yin and yang with oxygen as it is essential for life on earth but has a darker side: too low or too high a concentration of O2, and it becomes a danger to life. Its compounds handled by an untrained operator or the nefarious can lead to a tragic incident.
The term ‘oxidising agent’ is derived from the gas oxygen, which has a rich history, including lending its name to Great Britain’s mighty Brinsworth Oxygen Company, also known as British Oxygen Company (BOC), now part of the global Linde-Praxair conglomerate.
Today’s world faces challenges. We have an aging population at risk from the emergence of respiratory diseases from air-borne pollutants, asthma and smoke inhalation, which can result in lung diseases including COPD (Chronic Obstructive Pulmonary Disease, a term that includes Bronchitis and Emphysema, among other medical conditions). Oxygen is critical in both treating and managing such conditions.
With the increase in human, animal and agricultural diseases from bacterial, viral and sanitation/janitorial issues (including shared swimming baths); the use of 5.1 Oxidising Agents and 5.2 Organic Peroxides is growing markedly. They have become heavily deployed as disinfectants and anti-bacterial/viral agents on farms, kitchens, toilets, places of mass transit as well as our homes and offices and most recently deployed as a countermeasure against Covid-19.
The ubiquity of oxygen
In a former life (after Gas and Equipment Ltd was bought by Linde AG), I recall sitting with colleagues at a board meeting in Höllriegelskreuth outside the capital of Bavaria (Munich). We were discussing special gases production and their logistics throughout Linde AG’s European subsidiaries.
The head of Linde Special Gases Europe in the early 1990s was the renowned Dr Groll. It was a lively, if somewhat formal, gathering of senior chemists and engineers.
He closed the meeting with a question: ‘What is the most hazardous gas we manufacture and distribute in Europe?’
I listened as my colleagues breathlessly named problematic gases, such as silicon tetrahydride, diborane, arsine, phosphine, methyl bromide, fluorine and an array of highly unstable organometallics used in semiconductor fabrication such as WF6 tungsten hexafluoride et al.
He looked around the table and focused his steely Teutonic gaze toward me.
‘Herr Karim, you have been unusually quiet,’ he said.
Everyone laughed.
‘Oxygen,’ I said, matching his gaze.
The boardroom erupted in laughter; good natured but mocking.
Dr Groll stood up from the table raising his arms to silence the ridicule directed at me.
‘A typical British response. Always different to the rest of Europe. But Karim is correct,’ he said, turning to the smirking faces arrayed across the oval table. ‘The gases you all mentioned are terrible indeed if not handled carefully, but we manufacture, store and transport the gases you all named in small volumes. The cylinder and valve designs have safety as a key feature. Our production operators, depot and driving staff are well trained, as are the end users; professionals.
‘As Karim indicates, there is a special place for oxygen when we consider safety, due to the high volumes we produce and distribute. Within its ubiquity comes compliancy because it surrounds us in the air, and essential for life; but in LOX* and GOX* there also lies danger and you must ensure your managers and their staff, and our end-users treat this liquid, and this gas with the utmost respect. Thank you, Herr Karim because sometimes we can overlook the obvious.’
No one laughed at me again.
In prefacing this column, I am not only recalling a memory of a day now passed (but one strangely prescient when contrasted against the UK’s exit from the European Union) but also writing a little about oxygen to help others, as Dr Groll instructed ‘because in ubiquity can lie compliancy’.
*LOX = Liquid Oxygen
*GOX = Compressed Gaseous Oxygen
Background
Oxygen is a member of the chalcogen group (aka the oxygen family) in the periodic table, a highly reactive non-metal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium. At standard temperature and pressure, two atoms of the element bind to form di-oxygen, a colourless and odourless di-atomic gas with the formula O2. Di-atomic oxygen gas constitutes 20.8% of the earth’s atmosphere.
The composition of the air that surrounds us is:
Gas Chemical Symbol %
Nitrogen N2 78.084
Oxygen O2 20.947
Argon Ar 0.934
Carbon Dioxide CO2 0.0350
Others Noble Gases etc. Trace
As a compound (including its oxides) the element oxygen makes up almost half of the earth’s crust.
Oxygen is historically associated with Joseph Priestley who referred to it as ‘dephlogisticated air’. The name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and correctly characterized the role it plays in combustion.
Common societal uses of gaseous and liquified oxygen include production of steel, plastics and textiles; brazing, welding and cutting of metals; rocket propellant; oxygen therapy; life support systems in aircraft, submarines and spaceflight; cleaning substrates; and diving – and essential in chemical reactions (as an additive/substrate). It must be absent for certain manufacturing, food packaging or preservation processes to prevent oxidation reactions.
Oxygen is produced on commercial and industrial scale by a process termed ‘air separation’. To understand the process, we need to examine the boiling points of the major constituents of air – nitrogen, oxygen and argon.
The basic process of air separation commences with giant turbines sucking air from the atmosphere, followed by purification and cooling cryogenically until it’s in the liquid phase (‘liquid Air’). The next stage is passing the cold liquid air through an insulated fractional distillation column, from which liquid nitrogen, oxygen and argon are separated and collected.
Due to the high energy usage required in the air-separation process, these plants are normally situated close to a power station (to gain the lowest kWh cost) and/or a large volume user, e.g. near steel works, chemical or oil refinery complexes (where large volumes of nitrogen and oxygen are required commercially). It should be noted that the air surrounding a steel works, chemical plant or refinery has many impurities, so purification of the air sucked from the adjacent atmosphere needs to be considered.
The oxygen produced from an air-separation plant is a cryogenic liquid referred to as LOX. It can be supplied in bulk by insulated pipeline direct to the user (a steel works, for example) or by a cryogenic bulk tanker, an insulated Dewar vessel (akin to a super-insulated vacuum flask), or vaporised and compressed into high-pressure gas cylinders as GOX.
Considerations
Fire and oxygen enrichment
As I discussed in a previous column on Class 3 Flammable Liquids, we have become familiar with the ‘fire triangle’. Disregarding the anomaly of pyrophoric products (such as unstable organometallics, e.g. SiH4); oxygen needs to be present to allow combustion to occur. A fire starts by a spark, or a physical build-up of heat (generated by a physical or chemical reaction or process). It requires a fuel (e.g. a liquid or solid at or above its ‘flash point’). This is why oxygen (be it contained as a liquid in cryogenic tanks/Dewar vessels or compressed into gas cylinders) must be stored outside in a ventilated space to reduce the risk of oxygen enrichment or build-up. Rising above the nominal 21% oxygen level in the atmosphere has additional concerns:
a) The increase of fire hazard, as oxygen aids combustion. An atmosphere enriched with oxygen will ignite faster, as the O2 percentage level rises.
b) A narcotic effect upon humans occurs when the atmosphere is enriched with O2, and has serious implications to life if abnormally high
c) Increased risk of oxidation reactions with substrates that the O2 may come into contact with.
d) Cryogenic burns with LOX as liquid O2 has a boiling point of -183°C.
e) Inadvertent pressure release from cylinder/cryogenic vessel
Exothermic reaction
The risk of chemical (and physical) reactions with the presence of oxygen gas may seem obvious when we see it used in combination with acetylene in welding/cutting (oxy-acetylene]. But we must understand the risk that runaway or uncontrolled reactions can occur with compounds that contain oxygen. These are referred to as Class 5.1 Oxidising Agents, or even more reactive 5.2 Organic Peroxides. The ADR carriage and usage symbol for Class 5.1 oxidising agents gives a clue to the risk – the black flames on the yellow-diamond arise from the symbol for oxygen (O). Some Class 5.2 organic peroxides are so reactive that they require stabilisers/inhibitors and some can only be stored or travel by temperature control (kept refrigerated to reduce the evolution of the oxygen, they contain).
Both Class 5.1 and 5.2 react adroitly with organic matter, such as hydrocarbons (materials that contain both hydrogen and carbon, and in some cases nitrogen), such as (petroleum derived) oils and gases, skin tissue, greases, lubricants etc. I have yet to see a road or transport yard that is free from oil stains on the ground; in fact some road surface material contains hydrocarbon within the bitumen or asphalt formulation. Under certain conditions, an exothermic reaction can readily take place between Class 5.1 and 5.2 with Class 3 or 4, hence the ADR slang advice from label colour ‘Red and Yellow do not mix’ – a maxim based on the colour of the ADR diamonds.
An exothermic reaction is one that generates heat; the opposite is an endothermic reaction. If the heat is not dissipated, this leads to fire and can result in a thermal runaway, aka an explosion.
Common compounds that contain oxygen used in industry are Class 2 nitrous oxide (and mixtures of 50/50 nitrous oxide and oxygen, the so called laughing gas or pain-relief Entonox), fertilizer products such as Class 5.1 and derivatives of Class 5.2 ammonium nitrate* and potassium nitrate, cleaning products, disinfectants, bleaches, paint-related products, etchants – as well as haircare, mouthwash and skin products that contain hydrogen peroxide (and its related compounds).
The concerns regarding hygiene are showing growth in supply-chain volumes of cleaning/disinfecting products that contain oxygen, and therefore of an oxidising nature (5.1) as well as organic peroxides (5.2). This is in part due to the advent of Covid-19 across the globe, not just in terms of cleaning products but also as Class 2 where oxygen therapy is an essential medical tool (administering gaseous oxygen to the infected) to counter severe respiratory distress.
Asphyxia, MAP & nitrogen blanketing
As we mentioned, oxygen as a gas (GOX) or cryogenic liquid (LOX) must be stored in well-ventilated areas, because of the dangers of oxygen enrichment by operational activity as well as leakage.
The converse, oxygen depletion, can occur leading to medical conditions such hypoxia, anoxia and anoxemia. This is when oxygen elimination occurs, such as the use of nitrogen blanketing (removal of the oxygen to prevent oxidation of a product or reducing possible side-reactions in a vessel), or in food manufacturing when Modified Atmosphere Packaging (MAP) is deployed. Examples are packets of crisps and supermarket ready meals, where gaseous nitrogen is pumped inside the packaging before the food is sealed for transport. The elimination (or displacement) of oxygen increases shelf life by reducing (or removing) the oxygen, to slow the oxidation of the food.
‘Oxygen cleaned’
Equipment used with oxygen, such as regulators, hoses, pipework and measuring instruments/apparatus et al. must be ‘oxygen cleaned’. This term refers to the removal of any dirt, hydrocarbon-based lubricants, greases and waxes from surfaces that may come into contact with O2, because the maxim ‘red and yellow do not mix’ is valid.
Oxygen will react with these materials aggressively, especially if under pressure (or subject to elevated temperature). The oxygen cylinder and liquid vessels always have the ‘Use no Oils or Greases’ warning labels. Because of the ubiquity of the oxygen cylinder as GOX (and nitrous oxide NOX) as well as LOX (cryogenically liquified O2) in medical use, there have been serious incidents in hospitals, when a dab of hydrocarbon-based moisturising hand-cream from a nurse or paramedic is inadvertently smeared on a valve when cylinders are being changed. Incidents in welding occur when oxygen and acetylene (an energetic hydrocarbon) come into contact in an accidental manner, usually by an untrained operator.
Security
There are security concerns in our current geo-political situation, regarding oxygen as LOX and GOX; as well as the oxidising agents (Class 5.1) and organic peroxides (Class 5.2) which when consigned in bulk are termed High Consequence Dangerous Goods (HCDG) under ADR/IMDG regulations. These products can be used nefariously (in-conjunction with other products) to pose a significant threat to society.
Resource links
CBA – The Chemical Business Association www.chemical.org.uk
CIA – The Chemical Industries Association www.cia.org.uk
BADGP – The British Association of Dangerous Goods Professionals www.badgp.org
BCGA – The British Compressed Gas Association www.bcga.co.uk
EIGA – European Industrial Gases Association www.eiga.eu
IFS/FIAS – International Fertiliser Society https://fertiliser-society.org
NCEC – National Chemical Emergency Centre https://the-ncec.com
RSC – Royal Society of Chemistry https://www.rsc.org
FTA – The Freight Transport Association www.fta.co.uk
RHA – The Road Haulage Association www.rha.uk.net
And of course
HSE – Health & Safety Executive advice on Welding, Chemicals, Transport, Warehousing, Agriculture, Hospitals and all Workplace issues (including compliance to the HSWA 1974) www.hse.gov.uk
Classes and acronyms
Bulk and Packaged Chemicals (aka Dangerous Goods) are subdivided under eight classes (generic types/risk), and subdivided within each class, with UN numbers under ADR and IMDG to specific products or in generic groupings (designated NOS):
Class 1 – Explosive substances or articles
Class 2 – Gases
Class 3 – Flammable Liquids
Class 4.1 – Flammable Solids, Self-Reactive and De-sensitized Explosives
Class 4.2 – Substances liable to spontaneously combust
Class 4.3 – Substances which in contact with water emit flammable and/or toxic gas
Class 5.1 – Oxidizing Substances
Class 5.2 – Organic Peroxides
Class 6.1 – Toxic
Class 6.2 – Biologically Infectious Substances
Class 7 – Radioactive
Class 8 – Corrosive
Class 9 – Miscellaneous dangerous substances and Environmentally Hazardous
ADR stands for Accord Dangereux Routier (European regulations concerning the international transport of dangerous goods by road). It is a UN treaty concluded in 1957 and updated ever since, according to new rules and regulations in the logistics industry.
IMDG stands for International Maritime Dangerous Goods (Code) and is accepted by MSC (Maritime Safety Committee) as an international guideline to the safe transportation or shipment of dangerous goods or hazardous materials by water on vessel.
NOS stands for Not Otherwise Specified.
If you require help, consultancy or insight into oxygen and its compounds or any industrial chemical, please feel free to contact me. If I can’t help, I certainly know someone (or an organisation) that can.
For more information, contact akarim1462@aol.com
About the Author
Ali S Karim BSc FRSC CChem FCILT FEI CSci Technical Consultant.
