In the thriving landscape of global trade today, goods flow like a tide between countries. However, a certain portion of these goods falls under special regulatory categories due to their inherent potential risks. This brings us to the crucial concept of “hazard classification,” which refers to the classification of dangerous goods.

I. Analyzing Hazard Classification

Hazard classification is a rigorous and systematic system. Its core task is to conduct a comprehensive assessment of the potential hazard characteristics of various chemicals and specific products and categorize them according to established standards. Whether it’s a construction site in a bustling metropolis or a small workshop in a quiet countryside, chemicals are widely integrated into all aspects of production and daily life. Due to their vastly different chemical structures and properties, the potential risks they carry also vary significantly.

Through hazard classification, we can accurately define these risks from multiple dimensions, including health, environmental, and physical aspects. For instance, some substances may corrode human skin, damage internal organs, and pose immediate or cumulative hazards to health. Others may contaminate soil and water sources upon leakage, bringing about long-lasting disasters to the ecological environment. There are also those with physical properties such as flammability and explosiveness, which could potentially trigger severe accidents with the slightest oversight. Based on these classifications, a series of subsequent scientific and effective risk management strategies can be formulated and implemented with precision.

Currently, the two mainstream classification models recognized internationally are the United Nations Model Regulations and the Globally Harmonized System of Classification and Labelling of Chemicals (GHS). Each has its own focus. The former focuses on ensuring the safe transfer of dangerous goods throughout the transportation chain, while the latter is more committed to the standardized management of chemicals throughout their entire life cycle, from the production source to the final disposal. Hazard classification runs through every stage of this process.

II. Analyzing the Hazard Classification of Dangerous Goods According to the United Nations Model Regulations

The United Nations Model Regulations, with their authority, systematically divide dangerous goods into nine major categories. Each category has its unique identification label and strict management requirements based on hazard classification:

1. Class 1: Explosives
   • Hazard Classification Characteristics: According to the hazard classification system, items in this category are clearly marked as highly explosive. They contain extremely unstable chemical structures. Even a slight external energy stimulus, such as a minor impact, friction, or a slight increase in temperature, can instantly trigger a violent chemical reaction. In this process, a huge amount of gas and astonishing heat will be released in an extremely short time, causing the pressure in the surrounding space to rise exponentially, leading to a powerful explosion. The destructive power is sufficient to level surrounding buildings in an instant, posing a deadly threat to life and property.
   • Examples: Fireworks and firecrackers, which add a festive atmosphere during holidays, fall into this high-risk category from the perspective of hazard classification. During their production, storage, and transportation, the safety regulations formulated based on their hazard classification must be strictly implemented. Even the slightest oversight could turn a festive occasion into a disaster scene.
2. Class 2: Gases
   • Subdivision and Hazard Classification Details: Further broken down according to hazard classification, this category includes 2.1 Flammable Gases, such as hydrogen and methane. These gases are highly active at standard temperature and pressure. Once they mix evenly with air, they are like “invisible bombs” that can burst into flames at the slightest spark.
   • 2.2 Non-flammable, Non-toxic Gases, such as nitrogen and oxygen, are relatively “mild” in general perception. However, as defined by hazard classification, under specific working conditions, for example, in a high-concentration environment or when reacting with certain substances, they may transform into oxidizers, promoting the spread of fire, or quietly deprive the human body of the normal oxygen supply, leading to asphyxiation risks.
   • 2.3 Toxic Gases, such as chlorine and ammonia, belong to the category of “poison kings.” According to the toxicity classification of hazard classification, once the human body inhales a small amount of these gases, they will quickly invade the respiratory tract, lungs, and even the entire blood circulation system, launching a fierce “attack” on the body’s cells, tissues, and organs, causing the poisoning symptoms to deteriorate from mild discomfort to life-threatening conditions.
   • Examples: The methane in common household gas is classified as a flammable gas according to hazard classification. Therefore, during the transportation and distribution process, based on its hazard classification characteristics, everything from the selection of pipeline materials and pressure regulation to the fireproof and explosion-proof facilities of transportation vehicles must be carefully arranged to ensure safety and prevent disasters caused by ignoring hazard classification.
   • The oxygen cylinders stocked in hospitals are classified as non-flammable but potentially risky gases according to hazard classification. When transporting them, the special requirements for their hazard classification must also be strictly followed to prevent collisions, leaks, and other accidents and ensure the safety of medical gas use.
3. Class 3: Flammable Liquids
   • Hazard Classification Characteristics: Many substances such as gasoline, alcohol, and paint are classified into this category according to hazard classification. These liquids have a low closed-cup flash point, which means that at room temperature, they are extremely volatile. The molecules break free from the liquid surface and disperse into the air to form a flammable vapor cloud. Once this “invisible cloud” encounters an open flame, an electric spark, or a high-temperature object, it will be ignited instantly, causing a raging fire that spreads extremely rapidly, bringing devastating damage to the surrounding environment.
   • Examples: Gas stations, which are the main storage and transfer nodes for gasoline, based on the hazard classification of gasoline, from the design of burying oil tanks underground, the construction of fire barriers, to the anti-static and anti-drip structures of fuel dispensers, every detail is carefully crafted according to the hazard classification of gasoline to minimize the risks during the transportation and storage of flammable liquids.
   • When paint manufacturers transport their products, they also need to conduct strict temperature control and anti-static treatment of the transportation vehicles according to the hazard classification of paint to ensure absolute safety.
4. Class 4: Flammable Solids; Substances Liable to Spontaneous Combustion; Substances Which in Contact with Water Emit Flammable Gases
   • Subdivision and Hazard Classification Interpretation: According to hazard classification, 4.1 Flammable Solids, such as red phosphorus and sulfur, have relatively weak chemical bonds in their crystal structures. They are extremely sensitive to external stimuli such as heat, impact, and friction. As long as the external conditions slightly exceed the normal range, they are likely to be ignited and become a source of fire, potentially causing larger fires.
   • 4.2 Substances Liable to Spontaneous Combustion, such as white phosphorus, have an extremely low ignition point based on hazard classification. Under normal temperature and pressure, as long as they come into contact with oxygen in the air, they will spontaneously initiate an oxidation reaction, continuously releasing heat until the temperature rises to the point where they can self-ignite.
   • 4.3 Substances Which in Contact with Water Emit Flammable Gases, such as sodium metal and potassium hydride, from the perspective of hazard classification, these substances have extremely high chemical reactivity. Once they encounter water or a damp environment, the chemical bonds inside will break and recombine violently, like “running wild horses,” releasing a large amount of flammable gas, such as hydrogen, accompanied by a surge of heat release, which is extremely likely to trigger an explosion.
   • Examples: Matches used for starting fires in daily life contain red phosphorus, which is classified as a flammable solid according to hazard classification. Throughout the entire process of match production, packaging, and transportation, a series of measures such as moisture prevention, heat insulation, and friction prevention must be taken according to its hazard classification characteristics to ensure safety.
   • When sodium metal is used in a laboratory or transported industrially, according to its hazard classification, the container must not only be absolutely dry but also have a high-strength sealing performance to prevent contact with external water vapor and cause disasters.
5. Class 5: Oxidizing Substances and Organic Peroxides
   • Subdivision and Hazard Classification Analysis: According to hazard classification, 5.1 Oxidizing Substances, such as ammonium chlorate and potassium permanganate, have extremely strong oxidizing properties. Their molecular structures contain atomic groups that are highly likely to capture electrons. When they encounter reducing agents or suitable temperature and humidity conditions, they will decompose rapidly, releasing a large number of oxygen molecules and heat. These “escaped” oxygen molecules are like “combustion-assisting elves,” which can make surrounding combustibles burst into flames in an instant.
   • 5.2 Organic Peroxides, marked by their unique divalent -O-O- structure, are recognized as thermally unstable molecules according to hazard classification. When the temperature rises slightly, they will decompose exothermically and self-accelerate like an “out-of-control nuclear reaction.” This decomposition process may not only generate explosive shock waves but also release toxic gases, causing multiple hazards to the surrounding environment.
   • Examples: In school laboratories, when students use potassium permanganate to produce oxygen, according to the hazard classification of potassium permanganate, teachers must strictly guide students to operate correctly and avoid mixing potassium permanganate with flammable, explosive, or reducing substances to prevent laboratory accidents caused by ignoring hazard classification.
   • During the transportation of chemical products, organic peroxides must be equipped with professional temperature control and explosion-proof transportation equipment according to their hazard classification to ensure their safety during transportation.
6. Class 6: Toxic Substances and Infectious Substances
   • Subdivision and Hazard Classification Elaboration: According to hazard classification, 6.1 Toxic Substances, such as arsenic trioxide and cyanide, can be called “deadly poisons.” After they enter the human body, according to the toxicity mechanism determined by hazard classification, they will skillfully bypass the body’s normal defense system, penetrate cell membranes, and “collude” with key biological molecules such as enzymes and receptors inside the cells, disrupting or completely destroying the normal physiological functions of the body. The poisoning symptoms range from mild nausea and vomiting to severe coma and death, gradually worsening.
   • 6.2 Infectious Substances, such as virus samples and bacterial cultures, belong to the high-risk category carrying pathogens according to hazard classification. They are like “invisible killers.” Once they leak or are improperly disposed of, these pathogens will spread rapidly among people and animal groups, triggering infectious disease outbreaks and posing a huge threat to public health security.
   • Examples: Medical waste generated by medical institutions often contains infectious substances. According to their hazard classification, a professional three-layer packaging method must be used to ensure that the pathogens will not leak. Special vehicles and personnel must be arranged to transport them along the specified routes. After the transportation is completed, the vehicles and sites must be strictly disinfected, and everything must be carried out in strict accordance with the norms formulated based on hazard classification.
   • In the production and transportation of pesticides, for those pesticide components classified as toxic substances according to hazard classification, toxicity labels, first aid measures for poisoning, and other information must be prominently marked on the packaging to prevent accidental ingestion and misuse.
7. Class 7: Radioactive Substances
   • Hazard Classification Characteristics: Radioactive substances such as uranium, cobalt, radium, and plutonium are separately listed as a category according to hazard classification. Their atomic nuclei are in an unstable state and will continuously emit alpha, beta, gamma, and other rays. These rays, according to the radiation hazard characteristics determined by hazard classification, have extremely strong penetrability and can penetrate human tissues, building materials, etc. unimpeded. Once the human body is exposed to their radiation for a long time, the DNA molecules in the cells will be damaged, leading to gene mutations, cancer, and other serious diseases. Moreover, this radiation hazard will continue to accumulate in the environment, having a profound impact on the ecological balance.
   • Examples: When nuclear power plants transport spent nuclear fuel, according to the hazard classification of spent nuclear fuel, the transportation container must adopt a special multi-layer composite structure made of lead, steel, etc., with super-strong radiation shielding capabilities. At the same time, the transportation route must be planned in advance to avoid densely populated areas, and the radiation dose must be monitored in real-time throughout the transportation process to ensure the safety of the surrounding environment and personnel. All these measures are carefully designed based on the hazard classification of spent nuclear fuel.
8. Class 8: Corrosive Substances
   • Hazard Classification Characteristics: Substances such as sulfuric acid, hydrochloric acid, nitric acid, and sodium hydroxide are classified as corrosive substances according to hazard classification. Their solutions contain a large number of hydrogen ions or hydroxide ions, which have extremely strong chemical activity. When they come into contact with human soft tissues such as the skin and eyes, according to the corrosion mechanism determined by hazard classification, they will quickly break the chemical bonds between cells, causing tissue burns and necrosis. When they encounter metal items, they will also, according to their hazard classification characteristics, erode the metal surface, causing it to rust and perforate, seriously affecting the service life of metal products.
   • Examples: In industrial production, factories often need to transport acid and alkali solutions. According to the hazard classification of acid and alkali solutions, the transportation containers must be made of materials with extremely strong corrosion resistance, such as glass fiber reinforced plastics, special stainless steel, etc., and must be equipped with a complete anti-leakage device, such as double-sealed valves, leakage detection sensors, etc., to prevent leakage accidents caused by corrosion and endanger the environment and personnel safety.
9. Class 9: Miscellaneous Dangerous Substances and Articles
   • Hazard Classification Characteristics: This category includes many substances that seemingly have nothing in common but actually have potential hazards, such as waste batteries, electronic devices containing harmful substances, and other items harmful to the environment, according to hazard classification. Although they do not belong to the eight typical categories of dangerous goods, they are still included in the regulatory scope according to hazard classification. This is because heavy metals such as mercury, cadmium, and lead in waste batteries will slowly seep out in the natural environment, polluting soil and water sources and causing chronic toxicity to the ecosystem. Toxic substances such as brominated flame retardants in toxic electronic devices will release toxic gases when incinerated or improperly disassembled, endangering the atmospheric environment. In addition, there are some substances with special risks during transportation that are difficult to simply classify into the previous eight categories and are also classified here according to hazard classification.
   • Examples: In the process of recycling electronic waste, according to the hazard classification of waste mobile phone batteries and other items, recycling enterprises must use special anti-static and anti-short-circuit packaging to collect and transport them separately from other ordinary waste, ensuring that environmental problems or safety accidents will not be caused by ignoring hazard classification during the recycling process.

III. Prohibitions Related to Hazard Classification in International Freight

Although the nine categories of dangerous goods classified according to hazard classification are not completely prohibited from international freight, to embark on a smooth cross-border transportation journey, a series of rules derived from hazard classification must be strictly adhered to:

1. Non-compliance with Packaging and Labeling Requirements
   When the packaging of goods does not meet the standards required for strength, tightness, cushioning performance, etc., based on their hazard classification, during long-distance transportation, with bumps and vibrations, there may be a risk of container breakage and cargo leakage. If the labeling is unclear and fails to prominently mark key information such as the hazard category, warning symbols, and emergency treatment measures according to hazard classification, once an emergency occurs during transportation, rescue personnel will not be able to quickly determine the risks and take effective measures, which is likely to lead to the deterioration of the accident. Goods that do not meet the packaging and labeling requirements of hazard classification will be prohibited from transportation once verified.
2. Prohibited Goods
   Certain goods determined to be extremely dangerous according to hazard classification may be used for illegal military purposes, severely damage the ecological environment, or violate international humanitarian principles. As a result, they are explicitly prohibited from trading and transportation by international conventions or the laws of importing countries. For example, some highly toxic chemical weapon raw materials are classified as strictly prohibited from circulation according to their hazard classification. Any attempt to smuggle such goods will be severely punished.
   There are also some dangerous items illegally transformed from endangered species products. According to hazard classification, they not only fall under the supervision of dangerous goods but also violate the laws and regulations for the protection of endangered species and will never be allowed to be transported through normal freight channels.
3. Exceeding the Carrying Limits
   Different means of transportation, whether it’s an airplane soaring in the sky, a ship navigating the sea, or a truck running on the land, have clear carrying limits and category scopes for dangerous goods classified according to hazard classification, based on their own designs, structures, and safety regulations. Once the transportation is overweight or exceeds the quantity limit, or incompatible dangerous goods are wrongly loaded together, for example, if a substance classified as a strong oxidizer according to hazard classification is loaded into the cargo hold of an airplane together with flammable substances, during the flight, once encountering situations such as air turbulence and temperature changes, it is extremely likely to trigger a violent chemical reaction, leading to accidents such as explosions and fires, endangering flight safety. Such dangerous goods that violate the carrying limits will inevitably be rejected for transportation.
4. Non-compliance with the Regulations of the Destination Country
   Each country and region formulates different regulatory standards for the import of dangerous goods based on their own unique environmental protection requirements, safety considerations, and industrial development policies, according to hazard classification. For example, EU countries, driven by their high standards for environmental protection, have much higher import standards for some pesticide-like dangerous goods formulated according to hazard classification compared to other regions. If such goods from exporting countries do not meet the import requirements of the EU , even if they are transported legally in their home countries, they will not be able to enter the EU territory once they arrive and can only be returned along the original route.

In conclusion, a thorough understanding of hazard classification is of great significance for ensuring the safety of the global supply chain, maintaining the health of the ecological environment, and protecting human life and property. Whether it’s the producers, transporters, or regulatory authorities of goods, they must perform their respective duties according to it and strictly abide by relevant regulations. Only in this way can dangerous goods be transported “smoothly” and “safely” between countries, and the stable development of global trade can be realized.