TruckandTrackSpring2020

Truck and Track Spring 2020 www.truckandtrack.com 64 DANGEROUS GOODS to form di-oxygen, a colourless and odourless di-atomic gas with the formula O 2 . Di-atomic oxygen gas constitutes 20.8% of the Earth’s atmosphere. The composition of the air that surrounds us – Gas Chemical Symbol % Nitrogen N 2 78.084 Oxygen O 2 20.947 Argon Ar 0.934 Carbon Dioxide C0 2 0.0350 Others Noble Gases etc Trace As a compound [including its oxides], the element Oxygenmakes up almost half of the Earth’s crust. Oxygen is historically associatedwith Joseph Priestley who referred to it as “dephlogisticated air”. The name oxygenwas 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, spaceflight, cleaning-substrates and diving – and essential in chemical reactions [as an additive/ substrate]. It must be absent for certain manufacturing, food packagingor preservationprocesses, toprevent 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, eg 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 eg 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 [eg 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 O 2 % level rises. [b] A narcotic effect upon humans occurs when the atmosphere is enriched with O 2 , and has serious implications to life if abnormally high [c] Increased risk of Oxidation reactions with substrates that the O 2 may come into contact with. [d] Cryogenic burns with LOX as liquid O 2 has a Boiling Point of -183 Degrees Celsius. [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 of runaway or uncontrolled reactions can occur with compounds that containOxygen. 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 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 contains both Hydrogen, 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, transport yard that is free from oil stains on the ground, in- fact some road surface material contains hydrocarbon within 01543 420 121 www.deker.co.uk VEHICLE FINANCE AND LEASING