Traffic Lights for Maritime Dangerous Goods Transportation: Which UN Numbered Cargoes Are Prone to Port Rejection?

In global maritime trade, the transportation of dangerous goods has become a high-risk link in port operations due to its complex safety control, environmental protection requirements, and regulatory constraints. As a key node in the maritime chain, ports’ acceptance standards for dangerous goods directly determine whether cargo can clear customs smoothly. According to 2024 statistical data from the International Maritime Organization (IMO), the average annual rejection rate of dangerous goods declarations by major global ports is approximately 3.2%. Among the reasons, the cargo properties corresponding to UN numbers (United Nations Dangerous Goods Numbers) are the core basis for port rejection decisions. Using the metaphor of “traffic lights”, this article systematically analyzes the types of UN numbered cargoes prone to port rejection, the reasons for rejection, and response strategies, providing practical guidance for logistics enterprises and shippers.

1. Core Judgment Dimensions for Port Rejection of Dangerous Goods

Ports’ acceptance of dangerous goods does not solely depend on the hazard class of the cargo, but comprehensively considers four core dimensions: regulatory compliance, safety control difficulty, emergency response capability, and environmental risk. Ports in different countries and regions have slight differences in rejection standards due to geographical location, infrastructure level, and regulatory policies, but all are based on the framework of the International Maritime Dangerous Goods Code (IMDG Code).

From a practical perspective, port rejection is usually divided into two categories: “absolute rejection” (red light) and “conditional rejection” (yellow light). The former refers to cargo that is definitely refused entry due to inherent properties or non-compliance; the latter refers to cargo that can only be accepted if additional regulatory requirements (such as special packaging, emergency plans) are met, otherwise it will be rejected. As the “identity code” of dangerous goods, the UN number, corresponding to cargo properties, transportation conditions, and risk levels, directly determines the cargo’s “access permission” at the port.

2. “Red Light Zone” Cargoes: High-Frequency Rejected UN Numbers and Typical Cases

“Red Light Zone” cargoes refer to dangerous goods that are listed as key interception targets by most ports worldwide due to extremely high risks and great control difficulties. Their UN numbers are often directly associated with properties such as explosion, high toxicity, and strong corrosion.

(1) Explosives: “Zero Tolerance” for UN0001-UN0168 Series

Explosives (Class 1 dangerous goods), due to their ability to release enormous energy instantly, have become the highest-level controlled objects in all ports. Cargoes with numbers such as UN0001 (Nitroglycerin), UN0081 (Trinitrotoluene, TNT), and UN0143 (Black Powder) are almost “categorically” rejected by all commercial ports globally.

A typical case occurred at the Port of Singapore in 2023: A logistics enterprise declared “industrial explosives” (actually UN0081), attempting to clear customs under the name of “low-sensitivity explosives”. Port X-ray inspection found that the cargo packaging did not meet the “Explosion-Proof Class I Packaging” standard specified in the IMDG Code, and the enterprise failed to provide the explosive transportation permit issued by the Ministry of Industry and Information Technology. The cargo was immediately rejected and a fine of SGD 500,000 was imposed. The core reasons for the rejection of such cargo are: first, the uncontrollable nature of explosion risks—even minor impacts or temperature changes may trigger accidents; second, most ports lack dedicated storage space for explosives and emergency explosion-proof facilities; third, under the international anti-terrorism situation, explosive transportation is classified as a high-risk security category.

It is worth noting that some Division 1.4 (substances with no significant hazard) explosives, such as UN0336 (Fireworks and Firecrackers), can be accepted through special applications at specific ports (e.g., Ningbo Port in China, Long Beach Port in the United States), but must meet strict conditions such as “limited quantity transportation”, “independent storage space”, and “24-hour security monitoring”. Once these limits are exceeded, rejection will still occur.

(2) Highly Toxic and Infectious Substances: Compliance Barriers for UN2814 and UN2900

Highly toxic substances (Division 6.1) and infectious substances (Division 6.2) in Class 6 dangerous goods pose severe threats to human health and public health, making them high-frequency rejection types at ports. Typical UN numbers include UN2814 (Potassium Cyanide Solution), UN2900 (Bacillus Anthracis Samples), and UN3287 (Toxic Biochemical Products).

European ports have the strictest controls on such cargo. Data from the Port of Rotterdam in 2024 shows that the port rejects approximately 40 batches of UN2814 cargo annually, with rejection reasons focusing on three aspects: first, failure to provide a “highly toxic substance safety assessment report” issued by an EU-recognized institution; second, failure to pass packaging tightness testing (requiring IP68 waterproof and dustproof rating); third, failure of the shipper to submit a “highly toxic substance emergency response plan” to the port 72 hours before declaration.

The rejection rate of infectious substances is even higher. UN2900 cargo, which may cause the spread of infectious diseases, can only be accepted by a few ports with Biosafety Level 3 (BSL-3) facilities (e.g., Port of Amsterdam in the Netherlands, Tianjin Port in China), and must provide certification documents from the World Health Organization (WHO) or local centers for disease control and prevention, otherwise direct rejection will occur. In 2023, the Port of Hamburg detained a batch of UN2900 cargo for 15 days due to the enterprise’s failure to provide “cold chain temperature records” (requiring a constant temperature of 2-8℃ throughout the process), and finally returned the cargo.

(3) Corrosive and Oxidizing Substances: Storage and Segregation Dilemmas for UN1789 and UN1482

Class 8 corrosive substances and Class 5 oxidizing substances are prone to port rejection due to substandard storage conditions, as they easily cause equipment damage and fire. Typical UN numbers include UN1789 (Sulfuric Acid), UN1824 (Sodium Hydroxide Solution), and UN1482 (Potassium Permanganate).

The core conflict leading to the rejection of such cargo is the “mismatch between segregation requirements and port facilities”. According to the IMDG Code, UN1789 (Sulfuric Acid) must be kept at least 10 meters away from flammable cargo, and the storage area must be paved with acid-resistant and corrosion-resistant ground. However, the dangerous goods warehouses of most small and medium-sized ports are general-purpose facilities that cannot meet the special segregation requirements. In 2023, Busan Port rejected 12 batches of UN1789 cargo, 8 of which were due to “no acid mist absorption device in the storage area” and 4 due to “insufficient 5-meter distance from UN1203 (Gasoline) storage space”.

Rejections of oxidizing substances are mostly related to “compatibility” issues. As a strong oxidizer, UN1482 (Potassium Permanganate) must be strictly segregated from reducing agents and organic substances. In 2024, the Port of Los Angeles discovered that a container was loaded with both UN1482 and UN1325 (Sulfur, flammable solid) simultaneously. The cargo was immediately rejected and the shipper was fined USD 200,000, on the grounds that “contact between the two cargoes may cause spontaneous combustion and explosion”.

(4) New-Type Dangerous Goods: Standard Lag Issues for UN3480 and UN3536

With the development of the new energy and new materials industries, new-type cargoes in Class 9 miscellaneous dangerous goods have become new hotspots for port rejection due to incomplete standards and difficult risk assessment. Among them, UN3480 (Lithium-Ion Batteries), UN3536 (Hydrogen Fuel Cells), and UN3316 (Nano Dangerous Goods) are the most typical.

The rejection rate of lithium-ion batteries (UN3480) has increased by 180% in the past five years. In 2024, the Port of Shanghai rejected 67 batches of UN3480 cargo, mainly for the following reasons: first, the State of Charge (SOC) of the batteries exceeded 30% (the upper limit specified in the 2022 edition of the IMDG Code); second, failure to use short-circuit-proof packaging; third, lack of a “thermal runaway test report”. Some ports, such as Jebel Ali Port in Dubai, even implement “seasonal rejection” for UN3480 cargo, suspending acceptance in summer (when the temperature exceeds 40℃), on the grounds that the risk of battery spontaneous combustion surges in high-temperature environments.

Hydrogen fuel cells (UN3536) involve high-pressure gas and flammable hydrogen. Most ports reject them due to the lack of “high-pressure container testing equipment” and “hydrogen leakage alarm systems”. In 2023, the Port of Sydney issued a clear notice stating that it only accepts UN3536 cargo with “ISO 19880 certification”, resulting in a rejection rate of 92% for non-compliant cargo.

3. “Yellow Light Zone” Cargoes: Conditionally Rejected UN Numbers and Control Requirements

“Yellow Light Zone” cargoes refer to dangerous goods with medium risk levels that are prone to port rejection due to non-standard declaration, substandard packaging, or lack of additional documents. Their UN numbers are concentrated in categories such as flammable liquids and flammable solids.

(1) Flammable Liquids: Declaration and Packaging Traps for UN1203 and UN1170

UN1203 (Gasoline), UN1170 (Ethanol), and UN1263 (Paint) in Class 3 flammable liquids are commonly used in international trade, but are frequently rejected due to declaration details and packaging issues.

As an extremely flammable liquid with a flash point below -18℃, UN1203 (Gasoline) rejection reasons are mostly declaration-related: first, failure to mark the “specific flash point value” and “explosion limit range”; second, failure to provide an “electrostatic grounding test report”; third, the deviation between declared weight and actual weight exceeding 5%. Among the 23 batches of UN1203 cargo rejected by Guangzhou Port in 2024, 17 batches were intercepted due to “failure to indicate ‘deck transport only’ on the bill of lading”.

Rejections of UN1170 (Ethanol) are closely related to packaging. The IMDG Code requires ethanol packaging to adopt a “leak-proof plug + vent valve” structure. In 2023, Qingdao Port found that an enterprise used ordinary plastic barrels to package UN1170 cargo and rejected it on the grounds that “the lack of a vent valve may lead to pressure accumulation”. The proportion of rejections due to non-compliant packaging accounted for 63%.

(2) Flammable Solids: Storage Temperature and Segregation Restrictions for UN1325 and UN1330

UN1325 (Sulfur), UN1330 (Red Phosphorus), and UN1479 (Guanidine Nitrate) in Class 4 flammable solids are often rejected due to port condition limitations, as they require strict control of storage temperature and segregation distance.

UN1325 (Sulfur) must be stored in an environment with a temperature not exceeding 35℃ and kept at least 5 meters away from oxidizers. In 2023, Mumbai Port rejected 19 batches of UN1325 cargo during the rainy season (when the temperature reached 38℃ and humidity exceeded 80%), on the grounds that “the warehouse lacks constant temperature and dehumidification facilities”. UN1330 (Red Phosphorus) is prone to spontaneous combustion when exposed to moisture and requires “waterproof packaging + desiccant filling”. All 11 batches of UN1330 cargo rejected by Singapore Port in 2024 were due to “damaged packaging leading to desiccant failure”.

(3) Gaseous Cargoes: Pressure Testing and Filling Compliance for UN1075 and UN1017

UN1075 (Liquefied Petroleum Gas), UN1017 (Ammonia), and UN1040 (Oxygen) in Class 2 gases are mostly rejected due to filling and testing issues, as they involve the safety of pressure vessels.

As a Division 2.1 flammable gas, UN1075 (Liquefied Petroleum Gas) must provide a “regular cylinder inspection report” (valid for no more than 5 years) and “filling weight records”. Among the 32 batches of UN1075 cargo rejected by Houston Port in 2023, 28 batches were due to “expired cylinder inspections”. UN1017 (Ammonia) has both toxicity (Division 2.3) and flammability (Division 2.1), and both class symbols must be marked on the packaging. In 2024, the Port of Rotterdam rejected UN1017 cargo due to the omission of the “Division 2.3 toxicity symbol”. Rejections caused by such “marking errors” accounted for 41%.

4. Regional Differences in Port Rejection: Control Characteristics of Major Global Ports

Ports in different regions have significant regional differences in rejection standards for UN numbered cargo due to different regulatory systems, industrial structures, and safety concepts. Shippers need to formulate targeted customs clearance strategies.

(1) European Ports: “Dual High Standards” of Environmental Protection and Compliance

European ports (e.g., Port of Rotterdam, Port of Hamburg) are known for their “strict environmental protection requirements” and “comprehensive compliance reviews”, and are particularly sensitive to UN numbered cargo involving environmental pollution. Cargoes such as UN2210 (Asbestos) and UN3077 (Environmentally Hazardous Substances, Solid) are almost rejected by all European ports. Even compliant UN1789 (Sulfuric Acid) must provide “marine pollution liability insurance certificates” and “leakage emergency response plans”, otherwise direct interception will occur.

In addition, European ports adopt a “zero tolerance” attitude towards “new-type dangerous goods not listed in the IMDG Code”. Before 2023, UN3536 (Hydrogen Fuel Cells) could only be accepted by the Port of Amsterdam, while other ports rejected them. Restrictions were gradually relaxed only after the EU issued special control standards in 2024.

(2) North American Ports: “Rigid Thresholds” of Security and Anti-Terrorism

Affected by anti-terrorism laws, North American ports (e.g., Port of Los Angeles, Port of New York) have strict controls on UN numbered cargo involving security risks. Cargoes such as UN0081 (TNT) and UN2814 (Potassium Cyanide) must pass the “Customs-Trade Partnership Against Terrorism” (C-TPAT) certification, otherwise they will be rejected. At the same time, North American ports have stricter restrictions on the State of Charge (SOC) of lithium-ion batteries (UN3480). The Port of Los Angeles clearly requires the SOC to not exceed 20%, which is lower than the 30% standard specified in the IMDG Code, resulting in many cargoes that meet international standards being rejected for failing to meet regional requirements.

(3) Asian Ports: Hierarchical Control and Seasonal Adjustments

Asian ports (e.g., Port of Shanghai, Port of Singapore) adopt a “hierarchical control + seasonal adjustment” model, implementing key interception for high-risk cargo while dynamically adjusting acceptance standards according to climatic conditions. The Port of Shanghai classifies UN3480 (Lithium-Ion Batteries) as “key controlled cargo in summer”, requiring additional “thermal stability test reports” from June to September; the Port of Singapore implements “rainy season transportation restrictions” for UN1203 (Gasoline). Due to the increased risk of static electricity in humid environments, an additional “anti-static grounding device” testing link is required.

(4) Emerging Market Ports: “Passive Rejection” Due to Facility Limitations

Rejections at emerging market ports (e.g., Port of Mumbai, Port of Rio de Janeiro) are mostly due to “insufficient infrastructure” rather than active control. Cargoes such as UN1482 (Potassium Permanganate) and UN1789 (Sulfuric Acid) are often rejected for “lack of dedicated storage warehouses”. In addition, the declaration systems of these ports are relatively backward, and the rejection rate due to mismatched UN numbers and cargo names (e.g., declaring UN1170 “Ethanol” as “Alcohol”) is as high as 75%.

5. Practical Strategies to Avoid Port Rejection: Full-Process Control from Declaration to Transportation

In response to the above rejection risks of UN numbered cargo, logistics enterprises and shippers need to establish a full-process control system of “pre-evaluation, in-process compliance, and post-emergency response” to reduce customs clearance resistance.

(1) Pre-Transportation: Accurate Evaluation of Matching Degree Between Port Acceptance Standards and Cargo Properties

1. Port Standard Inquiry: Inquiry about the acceptance requirements for specific UN numbered cargo through the IMO official website and the target port authority platform. For example, before submitting UN2814 cargo to the Port of Rotterdam, confirm the “list of highly toxic substance assessment institutions” in advance; when transporting UN3480 cargo to the Port of Los Angeles, verify the latest SOC limit standards.
2. Cargo Property Recheck: Entrust third-party institutions to test the core indicators of the cargo to ensure matching with the UN number. For example, accurately measure the