Road Tunnels Manual

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Hazards due to DG-transport

Dangerous goods or hazardous materials are solids, liquids or gases that can harm people, other living organisms, property or the environment, considering their chemical or physical properties. A substance or a material presenting a particular hazard should be used, handled or transported taking into account the characteristics of that hazard. A substance or a material is considered dangerous when it:

  • may cause damage to people who handle it,
  • may cause damage to third parties and their property,
  • may cause damage to the environment (atmosphere, soil, water, plants, animals, food chain);
  • may endanger transport safety,
  • may cause damage to the vehicle with which it is being transported.

A dangerous good can present more than one kind of hazard and therefore several risks. The different types of hazard that may occur during road transport are coded as:

  • D-explosiveness,
  • F-flammability,
  • S-spontaneous combustion,
  • SR-self reactive,
  • W-water reactive,
  • O-oxidizing,
  • P-organic peroxide,
  • T-toxicity,
  • I-infectious,
  • C-corrosivity.

The following table describes hazards posed by dangerous goods depending on their Class according to ADR classification.

Table 1: Hazards of Dangerous Goods classes

Class number

Class description

Hazard description

Class 1

Explosive substances or articles

• may cause undesired uncontrolled explosion,

• may cause gas expansion and generate blast wave,

• may cause property and physical damage,

• launch of fragments at high speed and long distances. 

Class 2


• they may be flammable,

• they may be oxidising or at risk of oxidation,

• in enclosed and closed rooms it can cause asphyxiation without being perceived,

• they may be toxic,

• if they are under pressure they may cause rupture (with possible explosion of the container),

• if they are refrigerated (cryogenic) they can endanger human tissues, or if the temperature of the container  increases rapidly the pressure may cause an explosion; these gases may also be flammable.

Class 3

Flammable liquids

• cause of fire.

Class 4.1

Flammable solids, self-reactive substances, polymerizing substances and solid desensitized explosives

• flammability,
• fire transmission,
• smoke,
• injuries,
• damages.

Class 4.2

Substances liable to spontaneous combustion

hazards of substances and articles of this Class are due to the possibility of their automatic ignition on contact with the air and without cause (spark or flame); on contact with oxygen they may self-ignite.

Class 4.3

Substances which, in contact with water, emit flammable gases

• creation of flammable gases,
• self ignition – fire.

Class 5.1

Oxidizing substances

• ignition,
• fire – smoke.

Class 5.2

Organic peroxides

• easy ignition,
• easy blast,
• violent burning.

Class 6.1

Toxic substances

• danger to human health,
• cause death when enter the body from the mouth, skin and nose within a few hours or days depending on the dose,
• high toxicity.

Class 6.2

Infectious substances

substances are hazardous because they contain micro-organisms (bacteria, parasites, viruses) that can cause infections in humans and animals; they may also contain bacteria, parasitic organisms or viruses without antidote in case of infection.

Class 7

Radioactive material

Hazards arising from the transport of contaminated radioactive substances
externally can cause:

  • environmental damage,
  • skin contamination,
  • other environmental and animal dangers that may occur even after a long period of time.

Radiation can affect humans externally or internally:

  • externally when the source is outside our body,
  • internally, when the body is exposed to radioactive material through inhalation, dust absorption, skin or eye damage and ingestion.

Class 8

Corrosive substances

• damage to the skin, eyes, mucous membranes and tissue necrosis,
• corrosion, burning of other materials.

Class 9

Miscellaneous dangerous substances and articles

• hazard to health if they enter the respiratory system (asbestos)
• source of poisonous gases in case of fire 


Reference sources

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