Truck and Track Autumn 2024 www.truckandtrack.com 60 DANGEROUS GOODS 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 % 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 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 that 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 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 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 to an endothermic reaction. If the heat is not dissipated, this leads to fire and can result in a thermal run-away, 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). *Ammonium Nitrate was tragically seen as the source of the tragic explosion in Beirut, Lebanon on 5th August 2020. 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 Coronavirus (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 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. An example being 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 etc 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. Other Oxidising Agents Gases: Fluorine, chlorine, ozone, nitrous oxide Liquids: Hydrogen peroxide, nitric acid, perchloric acid, bromine, sulphuric acid Solids: Nitrites, nitrates, perchlorates, chromates, dichromates, picrates, permanganates, hypochlorites, bromates, iodates, chlorites, chlorates, persulphates. Other Hazards ■ Compounds containing the functional groups: azide, acetylide, diazo, nitroso, haloamine, peroxide and ozonide are shock and heat sensitive and can explode violently. ■ Some organic compounds such as ethers, tetrahydrofuran (THF), and dioxan can react with oxygen (from the air) TRUCK & TRAILER SOLUTIONS WELCOME TOALLPORTS GROUP allportsgroup.co.uk
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