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Flammable solids of dangerous goods class 4

Dangerous goods class 4: flammable solids

| von Julia

In order to be able to classify the emanating danger of different goods and to create suitable specifications for storage and transport, these are divided into different dangerous goods classes.

Dangerous goods class 4 is one of the largest representatives – it contains flammable solid substances. It also categorizes three subclasses. Read here what falls under dangerous goods class 4, what labeling is necessary and what to look out for in traffic and in the event of damage.

Which substances fall under dangerous goods class 4?

Dangerous goods class 4 includes flammable solids that may be solid, self-reactive and desensitizing explosives. “Desensitizing explosive” refers to solid or liquid explosive substances that are phlegmatized so that their explosive properties can be suppressed. The purpose of this is to prevent a mass explosion while allowing them to burn at a low rate so that they are not classified in the “explosive substances” hazard class. In addition, there are subclasses that also include substances that ignite spontaneously and those that form flammable gases in contact with water.

This results in a rather extensive list, which is why dangerous goods class 4 is also considered the most extensive representative of this categorization under the European Agreement concerning the International Carriage of Dangerous Goods by Road (ADR). Examples of substances in this class include the following:

Substance Classification/subclass Where does the substance occur in everyday life?
Matches 4.1 e.g. matches
Sulfur 4.1 e.g. artificial fertilizer
Aluminum powder 4.1 e.g. for the production of paints and varnishes in model making
Coal 4.2 e.g. vegetable based barbecue charcoal
Fishmeal 4.2 e.g. certain fish waste
Phosphorus 4.2 e.g. in crop protection products
Calcium 4.3 e.g. as a food supplement
Zinc dust 4.3 e.g. in batteries
Sodium 4.3 e.g. as a food supplement

By the way, there are a number of other dangerous goods classes according to ADR, ranging from dangerous goods class 1 to dangerous goods class 9.

In comparison, most classes (such as dangerous goods class 3) are much less extensive, which does not always make the optimal handling of dangerous goods class 4 easy – in case of doubt, the real substance must be considered here, as the supercategory may be too extensive for special requirements.

Subclasses of flammable solids

Like most other classes of dangerous goods, Class 4 is differentiated into further subclasses. These range from subclass 4.1 to subclass 4.2 to subclass 4.3 and are characterized by the following properties:

Subclass 4.1

Division 4.1 includes flammable solids that have self-reactive and desensitized explosive properties. They are considered highly flammable and can cause a fire just by a spark or friction. In addition, substances that decompose exothermically through contact with impurities or through exceptionally high temperatures also belong in this category.

Another important representative is explosive materials that have either been moistened with water or alcohol or contain sufficient plasticizing or inerting agents that the explosive properties are suppressed. Common examplesof mixtures and chemical substances in Division 4.1 include sulfur, matches, rubber residues, and aluminum powder. However, substances that meet the properties of Hazardous Materials Class 1, are organic peroxides, or have a heat of decomposition of less than 300 joules per gram are exempt.

Subclass 4.2

Division 4.2 contains spontaneously combustible substancesand includes both solid and liquid mixtures and solutions. The criterion is that the substance can ignite in contact with air within five minutes. Likewise, this category includes representatives that exhibit self-heating properties in contact with air, as these substances can ignite in larger quantities over a long period of time. Typical examples are white phosphorus, fish meal, coal, metallic iron or varnishes.

These so-called pyrophoric substances are additionally subdivided into different packing groups in Division 4.2, which makes identification easier in the event of damage. This also affects the specifications for storage. A distinction is made between packing group I (self-igniting), II (self-heating) and III (less self-heating).

Subclass 4.3

Third in the group is Division 4.3, which includes articles and substances which, in contact with water, emit flammable gases. In combination with air, this creates an explosive mixture. For some substances, the heat alone in the mixture-water reaction is already sufficient to cause ignition of the resulting gas.

Examples of subclass 4.3 include sodium, calcium, zinc powder and by-products from aluminum production. As with Division 4.2, additional packing groups are differentiated according to the degree of hazard. For this subclass, these are packing group I (violent reaction), II (slight reaction) and III (slow reaction).

Problem in traffic

Especially in transport, dangerous goods class 4 offers some challenges that can quickly become problematic. Due to the self-decomposing, flammable or even explosive properties, attention must be paid to appropriate packaging for containers and means of transport: These must have ADR approval. In addition, legally mandatory labeling (for example, by GHS mark) and constant inspections apply.

In addition, standard equipment must be available for the transport of dangerous goods, which according to ADR must include, for example, high-visibility vests and warning triangles, suitable fire extinguishers, personal protective clothing, as well as a portable lighting device and load securing equipment. In addition, an ADR license is required for the truck driver.

Dangerous goods class 4 marking

For dangerous goods class 4,appropriate labeling must be provided in transport so that it can be directly assigned which hazards emanate from the respective substances and mixtures. In particular, the GHS signs are decisive for this, but also the individual signs for subclasses 4.1 to 4.3. Both must be clearly visible on the containers as well as on the outside of the truck.

By the way, not every truck driver is allowed to transport dangerous goods. Instead, only those drivers who have obtained anADR license in an ADR training course may be used. They must also have special ADR equipment and have been instructed on what to do in the event of damage and the correct departure check.

Behavior in the event of damage

Due to the different properties of the individual goods in subclasses 4.1 to 4.3, the behavior in the event of damage is also not always the same. It is important to address the particular properties of the substancesand to consider some basic behaviors for flammable substances. The following overview can be considered as orientation:

  • Division 4.1: If damage occurs with substances in this division, water must not be used for extinguishing. Otherwise, this could promote the explosive capabilities of the hazardous material.
  • Division 4.2: Since the spilled hazardous material is self-igniting, special care must be taken. In the event of a cargo spill during transportation, not only should extreme care be taken, but a suitable dry chemical should also be used. Water must never be used for extinguishing.
  • Division 4.3: Water is not suitable for extinguishing substances in this category. Instead, a special extinguishing agent must be used. These include, for example, special powder or dry sand. In the event of damage, be sure to keep corresponding hazardous substances away from sources of ignition.

Hazard class 4 is the most extensive hazard class

Dangerous goods class 4 is not only one of the most comprehensive representatives according to ADR, but also includes some substances that are frequently encountered in everyday life. In the three subclasses a) flammable solids, (b) substances liable to spontaneous combustion and (3c) substances which, in combination with water, form flammable gases, are grouped together.

Not least for this reason, it is elementary for storage and transport to rely on appropriate safety precautions, labeling and expertise. This is the only way to optimally meet the respective hazard characteristics.


Dangerous goods class 4 groups together flammable substances, which in turn are divided into three subclasses. These include flammable solids (Division 4.1), substances liable to spontaneous combustion (Division 4.2) and substances which, in contact with water, emit flammable gases (Division 4.3). Common examples include sulfur, coal and sodium.

Flammable solids include those hazardous materials that can already be ignited by a sparkor cause a fire when exposed to friction. In addition, there are self-decomposing substances that tend to undergo highly exothermic decomposition at high temperatures or when contaminated. In addition, oxygen or water can cause inflammation.

Hazard classes are used to indicate the type of hazard to human health,hazard to the environment, or physical hazard posed by a particular mixture or chemical substance. In addition to hazard classes, there are also hazard categories, which provide a finer subdivision. Incidentally, hazard classes become important when it comes to the transport of dangerous goods.

Hazardous substances, in turn, form the basis for the categorization of hazard classes and include mixtures and chemical substances that can have a harmful effect on humans and/or the environment when used (or even manufactured). In addition, there are substances with a specified limit value and those articles that meet specified criteria according to Regulation (EC) No. 1272/2008 (CLP).

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