The Red Line of Life Safety: An Analysis of the Ten Reasons Why High-Risk Gases Are Blacklisted in Transportation

I. Preface: The “Safety Dilemma” of High-Risk Gas Transportation and the Necessity of the Blacklist System

As special raw materials in industrial production, scientific research experiments, and other fields, high-risk gases (such as highly toxic gases, flammable and explosive gases, and corrosive gases) are always accompanied by extremely high safety risks during transportation. According to 2024 statistical data from the International Association for Dangerous Goods Transport (ADR), global annual casualties caused by high-risk gas transportation accidents exceed 2,000, with direct economic losses reaching 5 billion US dollars. Among these accidents, 70% result from explosions, poisoning, or environmental pollution caused by gas leaks.

To uphold the red line of life safety and public interests, countries around the world have successively established a “blacklist system” for high-risk gas transportation. This system prohibits the circulation of gas types whose safety risks exceed controllable limits and whose harmful consequences are irreversible through public transportation channels such as roads, railways, aviation, and maritime shipping. Far from being a simplistic “one-size-fits-all” regulation, this system is a scientific decision based on multi-dimensional factors including risk assessment, accident cases, and regulatory standards. This article will delve into the ten core reasons why high-risk gases are included in the transportation blacklist, revealing the underlying logic of “putting life first and prioritizing risks” behind transportation regulation.

II. Reason 1: Highly Toxic Properties Cause “Irreversible Harm,” Threatening Human Life Safety

Highly toxic gases are frequent entries on the transportation blacklist. Their core risk lies in the fact that “even minimal exposure can cause severe harm or death,” and the consequences of poisoning are irreversible. Once a leak occurs, they pose an immediate threat to the lives of transport personnel, residents along the route, and rescue workers.

The toxicity of such gases is usually measured by the “median lethal dose (LD₅₀)” or “median lethal concentration (LC₅₀)”. Gases are classified as highly toxic when LD₅₀ < 50mg/kg (oral) and LC₅₀ < 1000ppm (inhalation, 4 hours). Examples include:

• Hydrogen cyanide gas: Its LC₅₀ is only 320ppm (1-hour inhalation). After inhaling it for 10 minutes, humans experience difficulty breathing and confusion, and respiratory failure leading to death can occur within 30 minutes. There is no specific antidote, and the survival rate after poisoning is less than 10%.
• Sarin gas (a nerve agent): Even at an air concentration of only 0.01mg/m³, exposure causes miosis (constricted pupils) and muscle twitching. At a concentration of 0.1mg/m³, death can occur within 2 minutes.

In 2021, a chemical company in Germany attempted to illegally transport 50kg of hydrogen cyanide gas. During transportation, a loose valve on the steel cylinder caused a gas leak, resulting in the immediate death of the truck driver. Thirty-two residents within a 2-kilometer radius around the leak site showed symptoms of poisoning, and over 1,000 people were evacuated urgently. Such accidents prove that the transportation risks of highly toxic gases exceed the controllable scope of “post-accident rescue.” Including them in the blacklist is a necessary measure to avoid large-scale casualties.

III. Reason 2: Flammable and Explosive Properties Easily Trigger “Chain Explosions,” Expanding the Scope of Accident Harm

Flammable and explosive high-risk gases (such as hydrogen, acetylene, and ethylene oxide) easily form flammable gas mixtures when their vapors mix with air. These mixtures can ignite and explode upon contact with open flames, static electricity, or high temperatures. Explosions are often accompanied by shockwaves and flame spread, creating a “chain reaction” that causes the scope of accident harm to expand exponentially.

The explosion risk of such gases is mainly reflected in their “explosion limits” and “ignition energy”:

• Wide explosion limits: For example, the explosion limit of hydrogen is 4.0%-75.6% (by volume), meaning that as long as the concentration of hydrogen in the air falls within this range, explosion conditions are met. The explosion limit of acetylene is 2.5%-82%, allowing it to explode at almost any mixing ratio with air.
• Low ignition energy: The minimum ignition energy of hydrogen is only 0.017mJ, which is 1/6 of the static energy generated by friction from chemical fiber clothing (approximately 0.1mJ). During transportation, collisions between steel cylinders caused by vehicle jolts and static buildup can all act as ignition sources.

In 2022, a logistics company in Texas, USA, illegally transported 200 cylinders of acetylene gas. A vehicle rear-end collision during transportation caused the steel cylinders to collide. The leaked acetylene mixed with air to form a flammable mixture, which exploded upon contact with a spark from the vehicle’s electrical system. The explosion shockwave damaged three nearby cars and injured 12 people. Additionally, the flames ignited nearby dry grass, causing a fire covering an area of 5 hectares, which took 36 hours to control. Such accidents demonstrate that transporting flammable and explosive gases not only endangers the safety of the transport itself but also causes “secondary harm” to public transportation and the surrounding environment. Including them in the blacklist can cut off the explosion risk chain at its source.

IV. Reason 3: Strong Corrosiveness Damages Transportation Containers, Increasing Leak Risks

Some high-risk gases (such as hydrogen fluoride, chlorine, and sulfur dioxide) have strong corrosive properties. They not only cause chemical burns to human skin and mucous membranes but also react chemically with transportation containers (such as steel cylinders and storage tanks). This reaction thins the container walls, reduces their strength, and triggers a vicious cycle of “container rupture—gas leakage.”

Take hydrogen fluoride gas as an example:

• Hydrogen fluoride reacts with iron on the inner wall of steel cylinders to form iron(II) fluoride (FeF₂), creating “corrosion pits” on the inner wall. It only takes 6 months for the wall thickness to decrease from 10mm to 5mm.
• The iron(II) fluoride produced by corrosion also causes “hydrogen embrittlement,” which makes the steel cylinder material brittle. This brittleness leads to cracks during transportation jolts, ultimately resulting in gas leakage.

In 2020, a chlorine gas leak occurred at a port in India. The cause was insufficient wall thickness of the chlorine transport cylinder due to long-term corrosion. The cylinder suddenly ruptured during hoisting, and the leaked chlorine formed a green toxic fog that spread to nearby residential areas. Fifty-eight people suffered respiratory burns, and 12 children were hospitalized with lung damage. Furthermore, leaked highly corrosive gases contaminate soil and water sources. For instance, after a hydrogen fluoride leak, the soil pH drops below 2, killing surrounding vegetation and requiring 5-10 years for soil remediation. Given the dual risks of “uncontrollable container corrosion” and “long-term environmental harm,” it is inevitable that such gases are included in the transportation blacklist.

V. Reason 4: Lack of Effective Emergency Response Measures, Making Post-Accident Rescue Extremely Difficult

Unlike ordinary dangerous goods (e.g., flammable liquids can be extinguished with foam, and toxic solids can be collected in sealed containers), some high-risk gases have “special physical and chemical properties” for which there are currently no mature emergency response technologies. Once a leak occurs, rescue workers struggle to control the risk in a short time, allowing the accident harm to continue expanding.

Typical cases include:

• Methyl chloride mixed gas: After leakage, this gas forms a toxic cloud “denser than air” and is highly volatile. Conventional “water curtain dilution” methods cannot effectively reduce its concentration, leaving “area blockade + natural diffusion” as the only disposal option. This process often takes hours or even days, during which nearby residents cannot return to their homes.
• Silicon tetrafluoride gas: When leaked, it reacts with water to form hydrogen fluoride and silicic acid, which not only increases toxicity but also forms “acidic droplets.” Rescue workers must wear heavy chemical protective suits (weighing over 20kg) to operate, which limits their mobility. Moreover, these suits only provide protection against hydrogen fluoride for 1 hour, making it difficult to sustain long-term rescue efforts.

In 2019, a silicon tetrafluoride gas leak occurred at Yokohama Port in Japan. Due to the lack of effective response measures, rescue workers could only set up a warning line 500 meters away from the leak site and allow the gas to diffuse naturally. This resulted in the shutdown of 3 nearby factories and a 12-hour suspension of port operations. Such “helpless” rescue dilemmas indicate that when the emergency response capacity for high-risk gases cannot keep up with transportation risks, including them in the blacklist is a rational choice of “choosing the lesser of two evils.”

VI. Reason 5: “Uncontrollable Factors” in Transportation, Making Risk Prediction Difficult

The transportation of high-risk gases involves the entire process of “loading—transportation—unloading.” Each link is fraught with uncontrollable factors such as extreme weather, road conditions, and equipment failures. These factors can break the “safe transportation threshold,” trigger accidents, and the risks are “sudden,” making them difficult to fully avoid through advance planning.

Common uncontrollable factors include:

• Impact of extreme weather: High-temperature weather (e.g., surface temperatures exceeding 40℃ in summer) increases the pressure inside gas cylinders. When the pressure exceeds the cylinder’s design pressure (usually 15MPa), the safety valve may fail, causing gas to spray out. Low-temperature weather (e.g., temperatures below -20℃ in winter) increases gas viscosity, clogging transportation pipelines and causing sudden local pressure surges in cylinders.
• Road jolts and collisions: On roads with poor conditions (such as mountainous or rural areas), vehicle jolts can reach an amplitude of over 10cm. This may loosen the fixing devices between cylinders and the vehicle frame, causing collisions between cylinders and damaging valves.
• Aging and failure of equipment: Aging of the transport vehicle’s braking system and tire pressure monitoring system can lead to sudden failures during long-distance transportation, resulting in vehicle rear-end collisions or rollovers, and subsequent cylinder rupture.

In 2023, an ammonia water transportation accident occurred in a province in China. The transport vehicle rolled over due to brake failure on a mountain road. The ammonia water cylinders fell into a gully and ruptured. The leaked ammonia water quickly vaporized, forming a toxic cloud. This caused crop wilting on 5 hectares of surrounding farmland and one villager to develop pulmonary edema from inhaling excessive ammonia gas. Such accidents prove that the “uncontrollable factors” in high-risk gas transportation exceed the boundaries of “technical prevention and control.” Including these gases in the blacklist is an effective way to reduce “unforeseeable risks.”

VII. Reason 6: Frequent Illegal Transportation, Making Regulatory Costs Far Exceed Safety Benefits

Although countries have formulated strict regulations for high-risk gas transportation (e.g., China’s Regulations on the Safety Management of Hazardous Chemicals require transport vehicles to be equipped with GPS positioning and emergency equipment, and drivers to hold special transport qualification certificates), some enterprises still take risks to illegally transport these gases to cut costs. This significantly increases regulatory difficulties and costs, while the regulatory benefits (i.e., safety guarantees achieved through regulation) are far lower than the investment costs.

Common forms of illegal transportation include:

• Unlicensed transportation: Enterprises without dangerous goods transport qualifications use ordinary trucks to transport high-risk gases. For example, in 2022, a logistics company in China used an ordinary box truck to transport 30 cylinders of ethylene oxide. The vehicle had no explosion-proof or leak-proof devices, and the cylinders were only covered with plastic sheeting.
• Overloaded transportation: To reduce the number of transport trips, enterprises arbitrarily exceed the rated filling capacity of cylinders. For instance, the rated filling capacity of an acetylene cylinder is 5kg, but some enterprises fill it with 7kg, causing the cylinder pressure to exceed the safe range.
• Fake documents: Enterprises forge “ordinary gas transport documents” to disguise high-risk gases as low-risk ones (e.g., passing hydrogen cyanide off as carbon dioxide) to evade regulatory inspections.

According to statistics from China’s Ministry of Emergency Management, over 1,200 cases of illegal high-risk gas transportation were investigated and handled nationwide from 2021 to 2023. Each case required 3 law enforcement officers to invest 5-7 working days in investigation, evidence collection, and punishment, resulting in extremely high regulatory costs. More seriously, even with increased regulatory efforts, the incidence of illegal transportation continues to rise at an annual rate of 8%. When “regulatory costs > safety benefits,” including high-risk gases in the blacklist and prohibiting their transportation from the source becomes a more efficient choice than “strengthening regulation.”

VIII. Reason 7: Strong “Destructiveness” to Public Infrastructure, Affecting Normal Social Operation

After a high-risk gas leak, it not only endangers human safety but also causes severe damage to public infrastructure such as roads, bridges, and pipe networks. This leads to traffic disruptions and suspended energy supply, further affecting normal social operation. The indirect losses caused by such incidents often far exceed the direct accident losses.

Examples include:

• Damage to roads by corrosive gases: After leakage, gases such as hydrogen fluoride and chlorine react chemically with road asphalt or cement, causing asphalt softening and cement spalling. This leads to potholes and cracks on the road surface. In 2020, a chlorine leak on a road section in Seoul, South Korea, damaged a 500-meter-long road surface, disrupting traffic for 48 hours and incurring repair costs of 2 million US dollars.
• Threat of flammable and explosive gases to pipe networks: After leakage, gases such as hydrogen and acetylene can diffuse into underground pipe networks (e.g., natural gas pipelines and sewage pipelines), potentially causing pipe network explosions and damaging energy supply systems. In 2019, an illegal hydrogen transport leak in a residential community in Philadelphia, USA, caused hydrogen to seep into underground natural gas pipelines, triggering an explosion. This destroyed 3 residential buildings and cut off gas supply to 500 households in the surrounding area for 3 days.

Public infrastructure is the “lifeline” of social operation, with long repair cycles and wide-ranging impacts. When the transportation risks of high-risk gases may lead to “social operation paralysis,” including them in the blacklist is a necessary measure to safeguard public interests.

IX. Reason 8: Inconsistent International Transportation Regulations, Making Cross-Border Circulation Risks Difficult to Control Collaboratively

In the context of globalization, the demand for cross-border transportation of high-risk gases is gradually increasing. However, differences in dangerous goods transportation regulations exist between countries/regions (e.g., the EU follows the ADR agreement, the US adopts DOT standards, and China implements GB standards). These differences create “regulatory blind spots” in cross-border transportation, making it difficult to control risks through international collaborative efforts.

Key regulatory differences include:

• Different packaging standards: The EU requires hydrogen cyanide gas to be transported in titanium alloy steel cylinders (compressive strength ≥20MPa), while some Southeast Asian countries only require ordinary carbon steel cylinders (compressive strength ≥15MPa). When gases are transported from the EU to Southeast Asia, the lower packaging standards increase leak risks.
• Different transport route approval processes: The US requires a 30-day advance application for cross-border high-risk gas transport route approval, while Mexico only requires 7 days. This discrepancy in approval timelines can disrupt transport plans and increase the probability of illegal transportation.
• Different emergency response standards: The EU mandates the use of alkaline solutions to neutralize chlorine leaks, while the US recommends water curtain dilution. When a leak occurs during cross-border transportation, inconsistent response standards among rescue workers may delay rescue efforts.

In 2022, a European enterprise transported 200kg of ethylene oxide from Germany to Poland (both EU member states). Due to differences in the two countries’ requirements for “emergency equipment on vehicles” (Germany requires 2 sets of gas masks, while Poland only requires 1 set), rescue workers lacked sufficient gas masks when a leak occurred during transportation. This prevented them from approaching the leak site promptly, prolonging the leak for 2 hours and disrupting cross-border highway traffic for 12 hours. Such collaborative control challenges caused by “inconsistent regulations” make it impossible to effectively reduce the cross-border transportation risks of some high-risk gases, ultimately leading to their inclusion in the blacklist by multiple countries.

X. Reason 9: Mature Alternative Solutions, Eliminating the Need for High-Risk Gas Transportation

With advancing technology, the industrial applications of many high-risk gases can now be achieved through “low-risk substitutes” or “on-site production technologies.” This eliminates the need for long-distance transportation of high-risk gases, providing “feasibility support” for their inclusion in the blacklist—ensuring no impact on industrial production needs while eliminating transportation risks.

Typical alternative cases include:

• Substitution of hydrogen cyanide: In the gold smelting industry, traditional processes use hydrogen cyanide to dissolve gold ore. Currently, a “thiourea process” has been developed, using thiourea (a low-toxicity chemical with LD₅₀=1200mg/kg) as a substitute for hydrogen cyanide. Thiourea can be transported by road with far lower risks than hydrogen cyanide.
• On-site production of acetylene: In metal cutting, traditional methods use transported acetylene gas. Now, “calcium carbide hydrolysis acetylene production” equipment can generate acetylene on-site through the reaction of calcium carbide (a low-risk solid) with water, eliminating the need for acetylene gas transportation.
• Substitution of ethylene oxide: In medical device sterilization, ethylene oxide (flammable, explosive, and highly toxic) is gradually being replaced by “hydrogen peroxide low-temperature plasma sterilization technology