Evaluation of Fires From the Perspective of Dangerous Goods Safety Advisor

In the general literature, fires are treated under definitions such as solid material fires, liquid material fires and gas fires as Type A, Type B, Type C fires. Naturally, this is the decision of the experts, but as a general principle, the fight against fire is primarily to take precautions before it starts or at least to extinguish it at the initial stage. This can contribute to fire safety by taking precautions before the fire starts, especially by paying attention to the measures recommended by DGSAs in the field for dangerous goods fires. For this, it increases the importance of preventive measures to be taken by examining the dangerous goods grouped under 9 classes according to the United Nations Model Regulations in terms of fire. 

Ahmet Cayık - Atlas Tehlikeli Madde Güvenlik Danışmanlığı

After our country became a party to the ADR agreement in terms of dangerous goods transport, it has introduced rules for Dangerous Goods Safety Advisers who should be involved in transport activities to be carried out by road. These rules include the same application of the rules in the annexes of the agreement, which was taken with the agreement of 54 countries at the stage of taking dangerous goods for operation, at the stage of unloading, packaging, loading, filling and sending. The purpose of this declaration is to explain an evaluation of dangerous goods evaluated in 9 different classes in terms of fire and especially the precautions to be taken before fire. 

Keywords: Dangerous Goods, Bleve, Explotion 

Hazardous Material Classes

The United Nations Model Regulations have classified hazardous materials worldwide. Although this classification is similar to the one made under the Globally Harmonized System (GHS), the United Nations (UN) conducts classification within the framework of the Manual of Tests and Criteria. Both methods essentially evaluate hazardous materials under the same outcomes. Hazardous materials are divided into 9 classes. The classes are explained below:

Class 1: Explosive substances and articles

Class 2: Gases

Class 3: Flammable liquids

Class 4.1: Flammable solids, self-reactive substances, polymerizing substances, and desensitized explosive solids

Class 4.2: Substances liable to spontaneous combustion

Class 4.3: Substances that emit flammable gases when in contact with water

Class 5.1: Oxidizing substances

Class 5.2: Organic peroxides

Class 6.1: Toxic substances

Class 6.2: Infectious substances

Class 7: Radioactive materials

Class 8: Corrosive substances

Class 9: Miscellaneous dangerous substances and articles

Risks and Basic Precautions of Hazardous Material Classes

Explosive Substances 

Risks: Risk of explosion, risk of fire, risk of being triggered by shock and friction.

Precautions: Explosive substances must be transported and stored in appropriate packaging. Smoking and the use of open flames should be strictly prohibited in areas where explosive substances are present.

Gases

Risks: Hazards related to transportation under pressure, fire, poisoning, or asphyxiation.

Precautions: Gases must be transported and stored in appropriate pressurized containers. Smoking and the use of open flames should be strictly prohibited in areas where gases are present. Ventilation is extremely important in enclosed spaces.

“The United Nations Model Regulations have classified hazardous materials worldwide. Although this classification is similar to the one made under the Globally Harmonized System (GHS), the United Nations (UN) conducts classification within the framework of the Manual of Tests and Criteria. ”

Flammable Liquids

Risks: Risk of fire and explosion; risk of poisoning from inhalation of vapors.

Precautions: Flammable liquids should be stored in cool and well-ventilated areas. Fire extinguishing equipment must be kept readily available.

Flammable Solids

Risks: Risk of fire; risk of ignition due to friction or impact.

Precautions: Flammable solids should be kept away from moisture and stored in appropriate packaging.

Oxidizing (Combustive) Substances and Organic Peroxides

Risks: Risk of fire and explosion; risk of reacting with other substances.

Precautions: Oxidizing substances should be stored separately from flammable materials. Appropriate protective equipment should be used.

Toxic and Infectious Substances

Risks: Risk of poisoning; risk of infectious diseases.

Precautions: Toxic and infectious substances should be transported and stored in leak-proof containers. Protective clothing and gloves must be used.

Radioactive Materials

Risks: Risk of radiation exposure; risk of environmental contamination.

Precautions: Radioactive materials should be transported and stored in lead containers.

Radiation detection devices must be used.

Corrosive Substances

Risks: Risk of burns to skin and eyes; risk of corrosion to metals and other materials.

Precautions: Corrosive substances should be transported and stored in durable containers.

Protective clothing, goggles, and gloves must be used.

Miscellaneous Hazardous Materials

Risks: Various physical and chemical risks.

Precautions: These materials should be transported and stored in appropriate packaging according to their characteristics. Safety instructions must be followed. These measures are crucial for the safe transportation and storage of hazardous materials. Compliance with up-to-date regulations and safety protocols is always required.

Fire Potential According to Hazardous Material Classes

Class 1 Explosives and Articles Fire Potential

Explosives and pyrotechnic materials are sensitive to impacts, shocks, collisions, friction, and heat. If exposed to these effects, an explosion may occur. A fire will inevitably start during the explosion. It is crucial to protect explosives from impact, collision, friction, and heat in storage areas. For explosives that are highly susceptible to explosion during transportation, transport units compliant with United Nations-based ADR regulations should be selected, and transportation should be conducted by trained authorized drivers.

In the case of a fire involving transported or stored explosives, no intervention should take place. Fire and AFAD units should be notified, and people should be evacuated for the safety of the surrounding environment and the facility. The general tendency for evacuation is to clear people at least 500 meters away for explosive fires involving 5 tons or less, and 100 meters away for fires involving more than 5 tons. It is also a critical protective factor that evacuated people remain behind a barrier and not be in the open.

If the potential fire has not yet spread to the explosives, the general rule is that facility workers can intervene using portable fire extinguishers. If a fire occurs during transportation in the vehicle's engine or tires, the driver may intervene in the same manner. However, the limit is based on the potential for the fire to reach the explosives. Once this potential is realized, fire extinguishing activities should cease. Unfortunately, for firefighters, the only thing they can do is to cool the area to prevent the fire from spreading and wait for the explosions to stop by trying to halt the chemical reaction.

Fire Potential of Class 2 Gases

Class 2 gases are categorized under three headings: flammable gases, toxic gases, and other gases. These typically fall under the definitions of asphyxiating and corrosive gases. In this section, our focus is on flammable gases. Flammable gases ignite when they find a suitable environment in terms of an ignition source and oxygen, according to the fire triangle principle. Therefore, it is essential to keep these gases away from fire and heat sources and prevent them from accumulating in the environment. This can be achieved through adequate ventilation.

As firefighters often say, burning gas is actually the safest gas, because the source and the distance it has reached can be seen. The lower and upper explosive limits of the gas and the amount of oxygen in the environment at these limits are critical factors in evaluating fire risks. When assessing the fire risks of gases, their relative weight compared to air becomes important. 

Gases lighter than air are not considered as excessively risky because they are unlikely to accumulate in spaces that are not completely enclosed. However, gases heavier than air tend to accumulate at the ground level or in deeper areas (such as channels or basements), leading to a high probability of flashover and ignition.

In order to transfer gases easily and economically, they must be liquefied to reduce their volume. For a gas whose volume can be reduced by up to 700 times, the risk of a leak increasing its volume by 700 times is a significant risk that must be considered during storage and transportation operations.

The highest risk potential in the pressure vessels used for gas transportation lies in their valves. In cases of dropping, striking, or tipping, if the valves break or come loose, the gas under pressure will rapidly evacuate and cause the pressure vessel to be ejected like a rocket. In this situation, aside from the physical damage to people and the environment, a rocket-like effect could occur, with flames trailing behind it if ignition occurs.

BLEVE (Boiling Liquid Expanding Vapor Explosion) explosions are the most risky type of explosion that could occur when pressure vessels heat up. As pressure vessels heat, the liquid gas inside tends to boil, resulting in an increase in vapor. The increased vapor pressure begins to push the vessel to its volumetric capacity, and the weakest point of the vessel breaks. The explosion creates a flammable environment that exceeds the vessel's volumetric capacity. This explosion represents the most undesirable explosion and fire scenario.

Fire Potential of Class 3 Flammable Liquids

Flammable liquids are commonly associated with substances such as gasoline and diesel. The flashpoints of the substances in this class are 60°C or lower. The most characteristic feature of these substances is their easy ignition when the fire triangle is completed. In other words, Class 3 substances can easily catch fire when oxygen, heat, and an ignition source come together. It is important to remember that no liquid itself burns. What burns are the vapors of the liquid. The lowest temperature at which the vapors of flammable liquids ignite when they encounter an ignition source is called the flashpoint. From this, we can conclude that substances with a low flashpoint are much more sensitive to the risk of combustion, while substances with a higher flashpoint are less favorable for fire. The vapor release capacity of flammable liquids can be up to 200 to 400 times their volume, which means that once these liquids ignite, the fire potential, combined with the oxygen in the environment that supports the combustion, can be roughly 250 times their volume.

The most risky combustion scenario for flammable liquids is the BLEVE (Boiling Liquid Expanding Vapor Explosion). When flammable liquid containers are exposed to heat, as the contents heat up, the evaporation rate increases and begins to expand in volume. When the safety valve’s capacity is insufficient, the container will burst at its weakest point, and unfortunately, the flammable liquid will be dispersed in vapor form. If the vapor encounters enough oxygen in the environment, it can cause a massive explosion. The explosion will naturally scatter the container’s walls like shrapnel.

When we examine the physical anatomy of flammable liquids, we can see that at the base of the flame, there is liquid waiting to evaporate but not yet burning. In the middle of the flame, there is a combustion that cannot be considered complete, but still relatively weak in terms of oxygen. At the tip of the flame, a complete combustion with an oxygen-rich environment can be observed. The combustion at the tip of the flame shows a more blue color, indicating complete combustion and sufficient oxygen. This knowledge will undoubtedly be useful in fire suppression stages.

An important consideration in the relationship between flammable liquids and fire is their behavior when exposed to water. Liquids lighter than water, liquids that can mix with water, and liquids heavier than water provide guidance on whether the fire can be extinguished with water. Generally, water is the most easily accessible and cost-effective fire-fighting substance. Firefighters want to be sure that they can extinguish the fire with water in the first instance. Flammable liquids lighter than water will float on water, and as more water is added, the burning area may expand, making it difficult to extinguish the fire. Water can extinguish Class 3 substances that mix with water because it reduces the density of the flammable liquid. For Class 3 substances heavier than water, water is naturally the ideal extinguishing agent.

Fire Potential of Class 4 Flammable Solids, Self-Reactive Substances, Polymerizing Substances, Reduced Sensitivity Solid Explosives, Spontaneously Combustible Substances, and Substances Releasing Flammable Gases When Reacting with Water

Class 4.1 substances consist of several subgroups that have flammability potential. The primary substances in this class are flammable solids. Flammable solids meet the definition of a Type A fire, as defined in the literature. They are solid substances that catch fire when exposed to a heat source. This class contains some surprises. For example, self-reactive substances are stabilized during the production stage through heat. They must not exceed a certain temperature. If the detected temperature is surpassed, the stabilization will break down, and self-reaction can begin. This reaction can be exothermic and may even result in an explosion. For this reason, self-reactive substances are packaged under quantity restrictions, and no more than 20 tons can be transported in a single transport unit.

Similarly, Class 4.1 substances include polymerizable substances. These substances tend to transition from monomer structure to polymer structure under normal transportation and storage conditions. They are usually stabilized by heat and must not exceed certain temperature values (SADT – Self-Accelerating Decomposition Temperature).

The fourth group of substances included in the class are reduced sensitivity solid explosives. Explosive materials are generally considered within Class 1.

“It is crucial to protect explosives from impact, collision, friction, and heat in storage areas. For explosives that are highly susceptible to explosion during transportation, transport units compliant with United Nations-based ADR regulations should be selected, and transportation should be conducted by trained authorized drivers.”

Class 4.2 substances include self-igniting materials. These materials, also known as pyrophoric substances, ignite upon contact with oxygen without the need for an external heat source. For example, substances like phosphorus can cause fires immediately when spilled or leaked. These can be considered the substances with the highest potential for combustion.

It is also important to mention self-heating substances defined in the same class. Wastes like oily rags, contaminated with oils, when stored in temporary storage areas under heat for an extended period, can cause an internal increase in temperature and ignite spontaneously. More caution is needed for these types of waste, and air-permeable packaging, like sacks, should be preferred. Packaging that provides thermal insulation should be avoided.

Class 4.3 substances produce flammable gases when reacting with water. For example, carbide produces acetylene gas when it reacts with water, and this gas is highly flammable. Normally, water should not be used as an extinguishing agent for fires involving these substances.

Fire Potential of Class 5 Oxidizing Substances and Organic Peroxides

Oxidizing substances are materials that contain a significant amount of oxygen, which can be transferred to the substances they come into contact with, facilitating their easy ignition. They are highly dangerous, as they can support the rapid combustion of flammable liquids and solids. The presence of oxidizing substances in spills or leaks can cause nearby dry grass, paper fragments, and dust to ignite easily. Even the pallets placed under these substances cannot withstand the material. 

Plastic or steel pallets should be preferred. Fires have occurred in situations involving wooden pallets during leaks. The definition of an accelerating substance might be a more suitable term for Class 5.1. Class 5.2 substances are organic peroxides. These are commonly used in the production sector, especially as bleaches. Organic peroxides are both flammable and oxidizing, meaning they are both combustible and capable of fueling a fire. Like the self-reactive substances in Class 4.1, organic peroxides are stabilized by heat and can cause exothermic decomposition, corrosion, and sometimes explosions when they react. An important warning should also be made regarding these substances: contact with the eyes can cause corneal damage and lead to blindness within a short period. It is highly advisable to keep eye wash solutions available in areas where organic peroxides are used.

Fire Potential of Class 6 Toxic and Infectious Substances

We do not generally expect a fire risk from a toxic substance alone. However, among chemicals that carry multiple hazards, there are those that are both toxic and flammable. Therefore, from a fire perspective, it is essential to consider that any product could pose multiple dangers, including flammability. This can be detected through the ADR labels and markings on hazardous materials packaging. If  a toxic and flammable liquid begins to burn, it should be anticipated that toxic smoke will also be released into the environment, and scuba-type oxygen masks should be kept ready for use.

Infectious substances are the least concerning in terms of fire risks. We do not expect any combustion event from them. However, in the case of a fire breaking out near the transport vehicle or storage area, immediate focus should be placed on extinguishing the fire to mitigate the risk of infection.

Fire Potential of Class 7 Radioactive Substances

Radioactive substances are present in almost every aspect of our lives. We use them in areas ranging from healthcare and food safety to security devices and energy production. Any leakage of radioactive materials has the potential to cause mass harm. Additionally, heat can trigger radioactive dispersion. Radioactive substances stored or made available in special packaging with lead plates can experience an increase in reaction if they heat up, protentially causing uncontrolled radiation spread.

Fire Potential of Class 8 Corrosive Substances

Class 8 substances are generally considered to have limited capacity to pose a fire risk. However, there is a potential secondary risk of flammability depending on the specific substance. Therefore, it is essential to identify whether the secondary risk of flammability exists for corrosive Class 8 substances by checking the ADR labels and markings on their packaging. For corrosive substances that pose a fire risk, preventive planning may be necessary. The corrosive properties of substances in this class can significantly harm human health. It is also important to remember that certain Class 8 substances can react with the natural moisture in the air, potentially creating corrosive environments.

Fire Potential of Class 9 Miscellaneous Hazardous Substances

Substances that do not meet the criteria to be included in the first eight classes but still possess hazardous characteristics are classified as Class 9. While we might think that Class 9 substances do not directly pose a flammability risk, substances within this class—particularly lithium batteries, polymer materials, and products like PCBs and PCTs—have significant fire potential.

“Infectious substances are the least concerning in terms of fire risks. We do not expect any combustion event from them. However, in the case of a fire breaking out near the transport vehicle or storage area, immediate focus should be placed on extinguishing the fire to mitigate the risk of infection.”

Lithium batteries hold a prominent place in Class 9. Under normal conditions, we wouldn't expect them to catch fire, but many of us have witnessed damaged or impacted lithium batteries igniting spontaneously. Especially with  the global work being done on energy storage, there are efforts to develop batteries that store energy more efficiently, last longer, and can be charged more quickly. While we can be more optimistic about primary batteries (non-rechargeable), rechargeable batteries, especially those made with polymer technology, continue to generate energy through reactions inside them. This allows the batteries to last longer and not deplete as quickly. However, carrying a battery in your mobile phone that generates energy through reactions means living with a potential fire risk. The most important aspect of lithium metal and lithium-ion batteries is that once they catch fire, it is almost impossible to extinguish them. Additionally, it would be useful to consider the corrosive and toxic vapors and smoke they release in case of combustion.

Class 9 also includes substances like polycarbonate biphenyls and polyhalogenated terphenyls, which are referred to as PCBs and PCTs. These substances, commonly found in transformers or transistors, are known to release dioxins when they burn, which are 1000 times more toxic than cyanide.

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