Why Are Fire Extinguishers Classified as Hazardous Goods? Analyzing the Safety Logic Behind Their Regulation

As critical equipment for fire safety protection, fire extinguishers are often associated with “safety and protection” in public perception. However, the fact that they are explicitly classified as “Class 2.2 Non-Flammable, Non-Toxic Gases” (UN 1044) under the international hazardous goods management system often confuses many people. This classification is not a denial of the fire extinguisher’s function, but rather a risk assessment based on its material properties and circulation scenarios—fire extinguishers rely on compressed or liquefied gases to deliver fire-suppressant agents, and when such gases are not under professional control during transportation, storage, or use, they may trigger safety accidents such as explosions, leaks, or physical injuries. This article will examine the core risk sources of fire extinguishers, break down the scientific basis for their classification as hazardous goods, and analyze how global regulatory measures are built around the “risk prevention and control” safety logic, providing a typical case reference for understanding the hazardous goods classification system.

I. Core Reasons for Fire Extinguishers Being Classified as Hazardous Goods: Material Properties Determine Risk Fundamentals

The hazardous goods attribute of fire extinguishers is essentially determined by the combination of their “compressed/liquefied gas carrier” material properties and the “potential for risk escalation in uncontrolled environments.” Whether carbon dioxide, dry powder, or water-based fire extinguishers, their core composition includes high-pressure gases or chemical components that can pose risks. When these components are not managed in accordance with standards, they release multiple safety hazards.

(1) “Physical Explosion Risk” of Compressed/Liquefied Gases: Inherent Hazards of Pressure Vessels

Most fire extinguishers use compressed gases (e.g., carbon dioxide, nitrogen) or liquefied gases (e.g., propane-derived suppressants) as propellants. These gases are sealed in metal pressure vessels and maintained at high pressure under normal conditions (typical operating pressure ranges from 1.2 to 15 MPa, far exceeding atmospheric pressure of 101.3 kPa), creating “pressure potential energy.” Once the integrity of the vessel is compromised, this pressure potential energy is released instantaneously, triggering a physical explosion—this is the primary reason fire extinguishers are classified as hazardous goods.

1. Explosion Impact from Vessel Rupture

Although fire extinguisher cylinders are designed to withstand pressure (usually requiring a hydrostatic test at twice the operating pressure), they may experience deformation, weld cracking, or valve damage during scenarios such as transportation 颠簸，impact, or high-temperature exposure:

• Transportation Phase: If fire extinguishers collide with other cargo in a freight vehicle or roll due to improper securing, the cylinders may withstand concentrated impact forces, causing local stress to exceed the material’s strength limit. For example, in 2023, a logistics company transporting carbon dioxide fire extinguishers failed to use anti-collision cushioning devices. When the vehicle braked suddenly, the fire extinguishers collided with metal shelves, causing the cylinder bases to crack. High-pressure carbon dioxide was released instantaneously, and the resulting shockwave pierced the vehicle’s side panels—fortunately, no casualties occurred;
• High-Temperature Environments: According to the ideal gas law (PV = nRT), the pressure of a gas in a sealed container is proportional to its temperature. When fire extinguishers are placed in sun-exposed containers (with internal temperatures reaching over 60°C) or storage environments near heat sources, the gas pressure inside the cylinders rises sharply. If this pressure exceeds the cylinder’s design limit (e.g., the pressure of a carbon dioxide fire extinguisher can reach 13 MPa at 60°C, approaching the burst pressure of some cylinders), a “physical explosion” may occur. Fragmentation velocity can exceed 300 m/s, resulting in extremely high penetration force.

2. Gas Leak Risks from Valve Failure

Valves are the core components controlling gas release in fire extinguishers and also represent a critical risk point. If valves fail due to manufacturing defects, corrosion, or improper operation, gas leaks may occur, leading to two types of risks:

• Asphyxiation Risk: While fire-suppressant gases like carbon dioxide and nitrogen are non-toxic, they quickly displace oxygen in enclosed spaces when leaked. For example, the leakage of one 4kg carbon dioxide fire extinguisher can reduce the oxygen concentration in a 10㎡ enclosed space from 21% to below 15%, potentially causing hypoxia and asphyxiation. In 2022, a warehouse worker illegally activated a carbon dioxide fire extinguisher for testing in a storage area. A valve malfunction caused continuous gas leakage, leaving two nearby workers dizzy and disoriented—they only recovered after emergency ventilation;
• Physical Injury Risk: High-pressure gas leaks generate high-velocity airflow, which can cause frostbite (e.g., carbon dioxide leaks cool to -78.5°C, leading to frostbite upon skin contact) or mechanical damage if directed at the human body. During maintenance of a dry powder fire extinguisher, a technician experienced a sudden valve rupture, and high-pressure nitrogen was sprayed onto their hand, causing second-degree frostbite.

(2) “Chemical and Physical Risks” of Fire-Suppressant Agents: Potential Hazards of Non-Gaseous Components

Beyond propellant gases, the fire-suppressant components in fire extinguishers may also compound risks, serving as supplementary grounds for hazardous goods classification. The risk characteristics of suppressants vary by fire extinguisher type, but all require regulatory oversight:

1. “Dust Contamination and Corrosiveness” of Dry Powder Agents

Dry powder fire extinguishers (e.g., ABC dry powder, BC dry powder) use suppressants primarily composed of sodium bicarbonate, ammonium dihydrogen phosphate, and other powdered substances. When leaked or misused, these substances pose two key risks:

• Dust Explosion Hazard: Although dry powder itself is non-flammable, if it forms a high-concentration dust cloud (e.g., exceeding 50 g/m³) in an enclosed space and encounters electrostatic sparks or open flames, a dust explosion may occur. In 2021, a chemical plant warehouse experienced a dry powder fire extinguisher cylinder rupture. The leaked suppressant formed a dust cloud, and a spark from nearby electrical equipment triggered a small explosion, collapsing warehouse shelves;
• Equipment Corrosion and Environmental Harm: Ammonium dihydrogen phosphate-based dry powder is weakly acidic, and long-term leakage can corrode metal equipment (e.g., electronic instruments, mechanical devices). A data center once experienced dry powder leakage from a fire extinguisher; unremoved powder entered server cabinets, causing circuit board corrosion and short circuits, resulting in data loss, equipment damage, and direct losses exceeding 500,000 yuan.

2. “Biological Contamination and Freeze-Expansion Risks” of Water-Based Agents

Water-based fire extinguishers (e.g., foam, water mist extinguishers) use water-based suppressants mixed with surfactants, preservatives, and other additives. Their risks primarily manifest in:

• Biological Contamination: If suppressants are improperly stored (e.g., due to cylinder seal failure), they are prone to bacterial and mold growth. In 2024, a hotel used an expired water-based fire extinguisher to put out a fire; the leaked suppressant contained mold spores, causing skin allergies in three on-site personnel;
• Freeze-Expansion Damage: Water-based suppressants freeze and expand at temperatures below 0°C, potentially cracking fire extinguisher cylinders. A logistics company in northern China failed to insulate water-based fire extinguishers stored outdoors in winter, causing 12 cylinders to crack. The leaked suppressant froze, disrupting transportation access.

(3) Dialectical Relationship Between “Functional Equipment” and “Hazardous Goods”: Risk Levels Depend on Scenarios

The uniqueness of fire extinguishers lies in their dual attribute of being both “safety equipment” and “hazardous goods”—at fire scenes, their fire-suppression function mitigates major risks; however, in non-fire scenarios (transportation, storage, disposal), their material properties may transform into risk sources. This shift between dual attributes depends on whether they are in a “controlled environment”:

• Controlled Environments (e.g., fire scenes, professional storage areas): When operated by professionals, fire extinguishers release propellants and suppressants in a designed manner, with risks strictly confined to “fire-suppression needs.” In such cases, their “safety equipment” attribute dominates;
• Uncontrolled Environments (e.g., general freight, unprofessional storage): Without professional protection and operational standards, the pressure risks of propellants and chemical risks of suppressants may escalate, making their “hazardous goods” attribute prominent.

The international hazardous goods classification system classifies fire extinguishers as hazardous goods based on dynamic “scenario risk” assessments—not to negate their safety value, but to establish regulatory measures for uncontrolled scenarios, preventing “safety equipment” from becoming “safety hazards.”

II. Safety Logic Behind Regulation: Full-Chain Prevention and Control from Risk Identification to Implementation

Global regulatory measures for fire extinguishers as hazardous goods are not simple “bans or restrictions,” but rather a full-chain safety logic built around “risk identification → risk assessment → risk control → risk emergency response.” These measures directly address the core risks of fire extinguishers, reducing risks to acceptable levels through standardized, professional oversight.

(1) Risk Identification: Defining “High-Risk Links” and “Key Control Points”

Regulatory systems first identify high-risk links and key control points throughout the fire extinguisher lifecycle through extensive accident data and experimental research, providing targeted foundations for subsequent measures:

1. Transportation Phase: Focusing on Three Major Risk Sources—”Collision, Temperature, and Stacking”

Transportation is the most risk-concentrated phase for fire extinguishers. Regulatory measures identify and manage risks through:

• Collision Risks: Accident statistics show that 70% of fire extinguisher transportation accidents are related to “unsecured or improperly secured cargo.” Therefore, the International Maritime Dangerous Goods (IMDG) Code explicitly requires fire extinguishers to be transported on anti-collision pallets, with a maximum single-pallet stacking height of 1.5 meters and cushioning materials between adjacent extinguishers;
• Temperature Risks: Laboratory tests indicate that for carbon dioxide fire extinguishers above 55°C, pressure increases by 0.3 MPa for every 1°C rise. Based on this, regulations mandate temperature monitoring devices in containers transporting fire extinguishers, which automatically trigger alarms and activate ventilation cooling systems when temperatures exceed 50°C;
• Stacking Risks: For fire extinguishers weighing over 10kg, stacking more than 3 layers may cause weld fatigue in bottom cylinders due to excessive load. Thus, the European Union’s ADR (Agreement Concerning the International Carriage of Dangerous Goods by Road) stipulates that fire extinguishers over 10kg must be stored in a single layer with anti-slip mats underneath.

2. Storage Phase: Managing Three Major Hazards—”Environment, Service Life, and Compatibility”

Risk identification in storage focuses on long-term storage hazards, with regulatory measures designing targeted requirements:

• Environmental Risks: Humid environments cause cylinder corrosion, particularly severe in coastal areas with high salt levels. China’s Code for Acceptance and Inspection of Building Fire Extinguisher Configuration (GB 50444) requires storage environments for fire extinguishers to have a relative humidity not exceeding 80%, with additional anti-rust coatings for coastal regions;
• Service Life Risks: Metal materials in fire extinguisher cylinders degrade over time, reducing pressure resistance. Fatigue tests show that carbon steel cylinders experience a 10% decrease in pressure resistance after 5 years and a 25% decrease after 10 years in normal service environments. Based on this, global regulations generally require hydrostatic testing every 5 years and mandatory scrapping after 10 years;
• Compatibility Risks: Mixed storage of different types of fire extinguishers may cause cross-contamination (e.g., dry powder absorbing moisture and caking when in contact with water-based extinguishers). Therefore, regulations require fire extinguishers to be stored in separate zones by type, with a minimum spacing of 1 meter between zones and clear labeling.

(2) Risk Assessment: Quantifying Risk Levels to Match Regulatory Intensity

Regulatory systems quantify fire extinguisher risk levels using “risk matrix methods,” determining regulatory intensity based on “occurrence probability” and “consequence severity” to avoid over-regulation or under-regulation:

1. Risk Probability Assessment: Scientific Prediction Based on Historical Data

Taking carbon dioxide fire extinguishers as an example, analysis of global transportation accident data over the past decade yields risk probabilities for different scenarios:

• Normal Transportation (compliant packaging and securing): Accident probability is 0.001 incidents per 10,000 units, with the main risk being minor valve leaks;
• Non-Compliant Transportation (no cushioning, excessive stacking): Accident probability rises to 0.05 incidents per 10,000 units, with risks concentrated in cylinder collision and cracking;
• Extreme Environments (temperatures> 60°C, severe 颠簸): Accident probability reaches 0.2 incidents per 10,000 units, potentially triggering explosions.

Based on this assessment, regulatory measures only require basic documentation for “normal transportation,” impose heavy fines for “non-compliant transportation,” and directly restrict transportation in “extreme environments” (e.g., prohibiting midday transportation during high-temperature summer periods).

2. Consequence Severity Assessment: Tiered Regulatory Measures

Fire extinguisher risks are classified into four levels—”minor, moderate, severe, extreme”—based on accident consequences, with matching regulatory measures:

• Minor Consequences (e.g., small gas leaks, no injuries): Regulatory measure: “Routine inspections,” requiring transport personnel to check cargo status every 2 hours;
• Moderate Consequences (e.g., cylinder deformation, localized leaks): Regulatory measure: “Emergency response,” requiring transport vehicles to be equipped with leak-sealing tools and ventilation equipment for rapid containment;
• Severe Consequences (e.g., cylinder rupture, large-scale gas leaks): Regulatory measure: “Transport restrictions,” requiring dedicated hazardous goods vehicles and at least 2 certified escorts;
• Extreme Consequences (e.g., explosions with fragment projection): Regulatory measure: “Special permits,” allowing transportation only on designated routes and during specified time periods, with advance notification to regulatory authorities.

(3) Risk Control: Mitigating Hazards Through “Technical Standards + Operational Guidelines”

Regulatory measures are not merely “restrictions,” but rather mitigate risks at the source through technical standards and operational guidelines, balancing “safety and efficiency”:

1. Technical Standards: Reducing Risks at the Design Stage

• Cylinder Material Standards: Require fire extinguisher cylinders to use high-quality carbon steel or aluminum alloy with a tensile strength ≥ 490 MPa, ensuring resistance to cracking under collision or pressure fluctuations. For example, the European EN 3 standard mandates that dry powder fire extinguisher cylinders pass a “-40°C to 60°C temperature cycle test” to ensure stable material performance under extreme temperatures;
• Valve Safety Design: Mandate valves to be equipped with “flow-limiting devices” that automatically close when gas leak rates exceed safe thresholds (e.g., > 50 g/s for carbon dioxide fire extinguishers). Additionally, valve interfaces must feature anti-misoperation designs to prevent activation by unqualified personnel;
• Pressure Relief Devices: Require fire extinguishers to be fitted with “rupture discs” or “safety valves” that automatically release pressure when internal pressure exceeds 1.2 times the design limit. For example, the rupture disc of a 4kg carbon dioxide fire extinguisher is designed to burst at 15 MPa, ensuring controlled pressure release rather than violent explosions.

2. Operational Guidelines: Managing Risks at the Process Stage

• Transport Operational Guidelines: Require hazardous goods transport drivers to complete “fire extinguisher-specific training” and master emergency leak response methods (e.g., wearing cold-resistant gloves and respirators for carbon dioxide leaks). Additionally, transport routes must avoid densely populated areas and tunnels to minimize accident impact;
• Storage Operational Guidelines: Require fire extinguisher storage areas to display “no open flame” signs and have “emergency exits” with a minimum width of 1.2 meters, as well as be equipped with dry powder fire extinguishers (for handling small fires caused by suppressant leaks). Storage managers must conduct monthly pressure checks and record cylinder pressure changes;
• Disposal Operational Guidelines: Prohibit random discarding or dismantling of expired fire extinguishers. Qualified enterprises must perform “gas recovery → cylinder cutting → material recycling” processes. For example, carbon dioxide fire extinguishers require gas recovery into dedicated storage tanks, and cylinders must undergo hydrostatic testing to confirm pressure relief before cutting, preventing explosions during dismantling.

(4) Risk Emergency Response: Building an “Early Warning → Response → Post-Incident” System

Regulatory measures also include comprehensive emergency mechanisms to quickly contain incidents and minimize losses when accidents occur:

• Early Warning Mechanism: Require vehicles transporting fire extinguishers to be equipped with GPS tracking and real-time monitoring systems, allowing regulatory authorities to remotely monitor cargo temperature and location. Alerts are triggered immediately for temperature anomalies or route deviations;
• Response Mechanism: Develop Guidelines for Fire Extinguisher Leak Emergency Response, specifying handling methods for different types of leaks (e.g., using vacuum cleaners to clean dry powder leaks and prevent dust dispersion; ventilating and cooling carbon dioxide leaks while restricting personnel access). Additionally, transport enterprises must establish coordination mechanisms with local fire departments to ensure on-site response within 15 minutes of an incident;
• Post-Incident Mechanism: Require enterprises to submit an Incident Report within 24 hours of an accident, analyzing causes and proposing corrective actions. Regulatory authorities conduct “rectification reviews” or “qualification downgrades” based on incident severity to prevent recurrence.

III. Lessons from Historical Accidents: Validating