In transport regulations dangerous goods are assigned to one of the nine classes according to the danger of the most predominant of the dangers they present.

• Class 1: Explosives (divided into Division 1.1 to 1.6)
• Class 2: Gases
• Class 2.1: flammable gases
• Class 2.2: non-flammable, non-toxic gases
• Class 2.3: toxic gases
• Class 3: Flammable liquids
• Class 4: Flammable solids; substances liable to spontaneous combustion; substances which, in contact
• with water, emit flammable gases
• Class 4.1: flammable solids, self-reactive substances and solid desensitized explosives
• Class 4.2: substances liable to spontaneous combustion
• Class 4.3: substances which, in contact with water, emit flammable gases
• Class 5: Oxidizing substances and organic peroxides
• Class 5.1: oxidizing substances
• Class 5.2: organic peroxides
• Class 6: Toxic and infectious substances
• Class 6.1: toxic substances
• Class 6.2: infectious substances
• Class 7: Radioactive material
• Class 8: Corrosive substances
• Class 9: Miscellaneous dangerous substances and articles

Dangerous Goods upon change in their physical properties either change the hazard class or may bring in additional risks. This will trigger change in UN Number assignment and emergency response.

Let us look at some examples.

Air

If we compress the air above 200 KPa it becomes Compressed Air and is assigned to UN 1002 Class 2.2

If we liquefy the air, then it turns to Refrigerated Liquefied Air is assigned to UN 1003 Class 2.2 with subsidiary risk 5.1.

Refrigerated liquefied air is more dangerous with its oxidizing property and can cause fire when it is leaked. Additionally, ship’s super structure exposed to it can turn brittle and effect the stability.

Metals – Iron

A piece of iron is not dangerous goods however if it is changed to powder it turns into pyrophoric metal. Liable to ignite spontaneously in air. If shaken, may produce sparks. In contact with water, evolve hydrogen, a flammable gas. Iron powder is classified as Class 4.2, substances liable to spontaneous combustion, UN Number 1383.

A container carrying iron powder if in any chance starts burning on board ship the advice is to let the container burn, do not try fighting the fire, if necessary cool the nearby containers with copious quantities of water. Never use water or foam directly to brining iron powder. Fire may be smothered with dry inert powdered material.

Metals – Aluminium

Aluminium on change of shape present different dangers and is equally nasty when involved in fire.

• Aluminium powder is pyrophoric Class 4.2
• Aluminium powder coated is Class 4.1
• Aluminium powder uncoated is Class 4.3
• Aluminium smelting by products are Class 4.3 and a waste which require notification under Basel convention.

When finely divided aluminium dust is scattered, it is easily ignited by naked lights, causing explosion.

Anhydrous & Hydrated

 Sodium sulphide is corrosive when hydrated and spontaneously combustible when anhydrous. Corrosive substances are assigned to Class 8 which can materially damage other goods and living tissue.