How are hazardous materials classified?

The acronym ADR stands for Agreement on Dangerous Goods by Road, which, translated into English, means Agreement on the Transport of Dangerous Goods by Road.

ADR is the European agreement originally signed in Geneva in 1957 that regulates the international transport of dangerous goods by road. Through this agreement, most European countries agreed on a set of common rules for the transport of hazardous substances by road within their territory and across borders. Complying with the ADR means taking into account the following aspects, which are of vital importance when transporting dangerous goods, so that they do not alter the safety of citizens, animals or the environment:

  • Know which products are considered hazardous and which can be transported by road.
  • The types of containers and packaging suitable for use.
  • Labeling and marking of both packages and vehicles for the transport of ADR goods by road. In the case of vehicles, an orange panel indicating the hazard identification number and the identification number of the goods must be displayed.
  • The necessary documentation to be able to transport these substances, as well as a consignment note, written instructions or permits relating to the authorization to carry out the transport.
  • To know which are the types of vehicles for the transport of chemical products as well as which are the special equipment for this purpose and which are duly certified.

In Spain there is a Royal Decree that requires compliance with the ADR; this agreement is revised from time to time (normally every two years) to take into account technical advances in this area, as well as the appearance of new materials, changes in labeling, etc.

The classification of dangerous goods is divided into 9 types, some of which include different subtypes within them.

Class 1: Explosive materials and objects

The first class refers to materials or objects that can release gases at temperatures or speeds capable of causing damage due to a chemical reaction. Also included are those materials that can produce exothermic reactions.

Likewise, within this same class, both materials and objects are subdivided according to different risks (mass explosion, projection or fire). Some of the examples we can find are fireworks, flares, bombs, rockets and detonators, among others.

Class 2: Gases

In this case, we refer to materials which, at normal pressure and at 20°C, are either in a gaseous state or with a vapor pressure exceeding 3 bar at 50°C. Gases can be found liquefied, compressed or refrigerated.

Depending on their properties, they can be classified as asphyxiating, oxidizing, flammable or toxic. Within this classification, three more divisions are established:

2.1 Flammable gases (Propylene, ethane, butane)

2.2 Non-flammable gases (Oxygen, helium)

2.3 Toxic gases (Chlorine)

Class 3: Flammable liquids

In this case we are talking about liquids with a flash point of 60º C. In addition, it must be taken into account that these materials may have toxic or corrosive characteristics, such as toluene, turpentine, gasoline, paints or varnishes.

Class 3 includes the following substances:

  • Flammable liquids
  • Insensitive liquid explosives

Class 4: Flammable solids, substances which may undergo spontaneous combustion and substances which in contact with water give off flammable gases.

In this fourth class of materials we find three different types:
Class 4.1: Flammable solids, self-reactive substances and solid desensitized explosive substances

In this case we find those that can react spontaneously. Due to their composition, they are solids which, under normal transport conditions, can become flammable and cause friction fires. These materials can be ignited by heat as well as by sparks or flames. Because they may contain self-reactive materials that can decompose exothermically under such effects or even by contact with other materials (such as acids, heavy metal compounds or amines), friction or shock, this can result in the release of noxious and flammable gases or vapors.

Class 4.2: Substances capable of spontaneous ignition

This subdivision includes so-called pyrophoric substances, i.e. substances that can heat up spontaneously under normal conditions of transport, or that can heat up by simple contact with air and become flammable. Examples include coal, ferrous metal shavings, wet cotton, etc.

Class 4.3: Substances which in contact with water give off flammable gases.

In this case, this subdivision covers various types of materials which, when in contact with water, give off flammable gases. Hazard panels usually incorporate an X preceding the identification of the hazard. Examples include barium, sodium, potassium, calcium carbide, etc.

Class 5.1: Oxidizing substances

They are liquids or solids that can cause or promote combustion; they generally give rise to reactions that release oxygen and, therefore, when in contact with other materials, increase the risk of fire, favoring the development of fires. An example would be ammonium nitrate.

Mixtures of oxidizing substances with combustible materials, or even with materials such as sugar, flour, edible oils and mineral oils, are dangerous.

On the other hand, in contact with liquid acids, most oxidizing substances produce a violent reaction that leads to the release of toxic gases.

Class 5.2: Organic peroxides

Organic peroxides are substances that can undergo exothermic decomposition at both normal and elevated temperatures. Decomposition can occur due to the effect of the heat itself, contact with impurities, friction or impact. These are materials derived from hydrogen peroxide, in which one or two of the hydrogen atoms are replaced by organic radicals. The risk involved is both at the level of constituting possible explosives as well as being corrosive or toxic.

Organic peroxides can be divided according to:

Not more than 1% of active oxygen comes from organic peroxides when its hydrogen peroxide content does not exceed 1%.
Not more than 0.5% of active oxygen comes from organic peroxides when their hydrogen peroxide content does not exceed 1%, but not more than 7%.

Due to their hazardous nature, there are limitations on the amount allowed for each transport unit.

Class 6.1: Toxic Substances

These substances, in relatively small quantities, are capable of damaging human health to the point of causing death by inhalation, skin absorption or ingestion. Examples are methanol or methylene chloride.

Due to their very nature, these materials pose a risk of poisoning if they come into contact with human beings. It should also be borne in mind that virtually all toxic substances give off toxic gases in the event of fire, or even if they are heated to decomposition.

Class 6.2: Infectious materials

Infectious materials refer to materials that contain (or are believed to contain) pathogens. These are microorganisms such as viruses or bacteria, capable of causing diseases in both animals and humans. An example of such materials could be found in diagnostic or test specimens.

There are biological products or products derived from living organisms that may require special treatment to be transported, such as materials for vaccine production purposes. Other materials included in this class would be laboratory cultures for the study of diseases (human or animal), patient specimens (materials that have been extracted from patients, both human and animal, such as blood, excrement or cellular tissues), microorganisms that have been genetically modified and waste of medical or clinical origin (all discarded material resulting from clinical practice on living beings or from biological research).

Class 7: Radioactive materials

In this case we refer to those materials or objects containing radionuclides whose activity concentration as the total of the consignment exceeds the minimum values that have been determined. Fissile materials are defined as the following:

  • Uranium 233
  • Uranium 235
  • Plutonium 239
  • Plutonium 241
  • Any combination of these radionuclides

In contrast, low-toxicity alpha-emitting materials are:

  • Natural uranium
  • Depleted uranium
  • Natural thorium
  • Uranium 235
  • Uranium 238
  • Thorium 232
  • Thorium 228
  • Thorium 230

Class 8: Corrosive materials

This kind of materials or objects can be harmful by simple contact with the skin, mucous membranes or eyes. They can also cause damage to other goods or even property if spilled; examples are sulfuric acid or sodium hypochlorite.

All substances included in this part of the classification have destructive effects, either to a lesser or greater degree, on materials such as metals or textiles. Not only do they cause damage if they come into contact with the skin or mucous membranes, but some of them are directly toxic or harmful. Ingesting or inhaling the vapors they produce can lead to poisoning; some of these materials can even penetrate the skin.

Class 9: Substances and objects presenting various hazards

Finally, Class 9 includes all those materials that pose a hazard or risk that have not been included in the previous categories. These include dioxins, fine dusts capable of causing damage to the respiratory tract and lithium batteries. The most common commodity found in this category is dry ice, used to refrigerate different products.

Here we can also find substances that require temperatures of 100 °C for transport; finally, we also refer to those organisms that have been genetically modified, but which nevertheless do not fall under the definition of infectious substances. Nevertheless, they may cause changes in animals and plants that would not occur naturally.

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