Acrylonitrile, stabilized, CAS RN 107-13-1, is transported under UN 1093 as a Class 3 flammable liquid with subsidiary Class 6.1 toxic risk and Packing Group I. The regulatory envelope covered by “Acrylonitrile UN 1093: Class 3 + 6.1 Labelling, Documents and Carrier Rules” begins with the Hazardous Materials Table at 49 CFR §172.101 and the ADR Table A of Chapter 3.2. The proper shipping name is “Acrylonitrile, stabilized”; the word “stabilized” is not optional. The material has a vapor pressure of 11.6 kPa at 20 °C, a boiling point of 77.3 °C, a liquid density of 0.806 g cm⁻³ at 20 °C, a relative vapor density of 1.83 (air = 1), and lower and upper explosive limits of 3.0 vol% and 17.0 vol%. The flash point is below 23 °C, placing the liquid in the Flam. Liq. 2 H225 category. Acute toxic effects support H301, H311, and H331, while the carcinogenicity endpoint supports H350 under the CLP entry. The dual hazard classification means a single-package carrier must manage both fire and toxic-inhalation outcomes simultaneously; this is not a rhetorical phrase but a packaging and stowage requirement.

Carriers occasionally confuse UN 1093 with UN 1092 acrolein because both are stabilized unsaturated compounds with flammable-toxic profiles; however, the primary and subsidiary classes are reversed. Acrylonitrile is Class 3 with subsidiary 6.1, while acrolein is Class 6.1 with subsidiary 3. This distinction changes the label order, the placarding hierarchy, and some packaging selection rules. A shipping paper that lists only “acrylo” without the full proper shipping name must be rejected; the exact UN number and proper shipping name are required on the document. The relevant special provisions require stabilization and shipper certification of inhibitor content.

Non-bulk packages moving under UN 1093 display the Class 3 flame label and the Class 6.1 skull-and-crossbones label on the same face of the outer packaging, adjacent to the UN number and proper shipping name. The marking must remain legible after exposure to water spray and sunlight; carriers reject packages with labels that are folded around a corner or obscured by stretch film. Combination packagings containing liquid volumes above 4 L carry orientation arrows on at least two opposite vertical sides under ADR 5.2.1.7.1 and 49 CFR §172.312. Because Packing Group I applies, the packaging must bear an X-coded UN specification marking; an X code verifies that the design type has passed the highest severity of drop, leakproofness, and stack tests for the packaging class. Closure systems for drums and IBCs are closed-vapor systems rather than open-vent systems. Venting closures are inappropriate for a PG I flammable-toxic liquid because normal daytime temperature rise would release vapor above occupational exposure limits and, in a confined freight container, could reach a flammable concentration. PTFE-lined caps and fluoropolymer gaskets are used where elastomer swelling is a documented failure mode; nitrile rubber may provide only short-term splash resistance, and the shipper must verify compatibility with the actual batch formulation. A drum with a damaged gasket, a missing tamper seal, or an unreadable UN marking is refused at the loading gate.

Bulk placarding differs from package labeling. A tank car, cargo tank, portable tank, or IBC containing UN 1093 in the United States requires a Class 3 placard under 49 CFR §172.504; the Class 6.1 subsidiary placard is applied when the table specifies the subsidiary hazard label for a bulk package. Placards are square, with a minimum side dimension of 250 mm under ADR 5.3.1.7.1; labels on packages are 100 mm × 100 mm under ADR 5.2.2.2.1.1. In ADR/RID carriage, orange plates are fixed to the front and rear of the tank vehicle and display the hazard identification number 336 in the upper half and UN 1093 in the lower half. The HIN 336 identifies a highly flammable liquid with toxic properties, and the carrier must not operate with a plate that is cracked, overpainted, or flipped out of view. For an ISO tank container moved by road and sea, the placards are fixed to all four sides of the frame; if the tank is placed on a trailer with only the front and rear visible, the side placards remain on the container itself.

What must the carrier verify before accepting a road tanker of UN 1093?

Before the loading line is connected, the carrier verifies the driver’s ADR training certificate under ADR 8.2.1.1, the vehicle approval certificate under ADR 9.1.2, and the presence of the instructions in writing under ADR 5.4.3.4. The consignment note must include the data elements arranged as ADR 5.4.1 prescribes: proper shipping name, UN number, class 3, subsidiary class 6.1, packing group I, number and type of packages or tank compartments, total quantity, shipper, and consignee. The carrier checks that the bottom valve is closed, the vapor return line is capped, and the tank is not leaking at the manlid gasket. Ullage calculation is a pass/fail item; a tank filled to the maximum at 10 °C can exceed the allowable filling degree at 35 °C if the shipper has used an incorrect expansion coefficient. The tank must have a previous-cargo and cleaning certificate showing that the last three loads did not contain alkaline or amine residues. Acrylonitrile is base-sensitive and can polymerize when contaminated with caustic or amine film; even a dried sodium hydroxide heel can act as an initiation site. The carrier also confirms that the vehicle carries two self-standing warning signs, a wheel chock, and a drain seal because these items are required equipment under ADR 8.1.5 and are checked during roadside inspections. A route plan must account for the ADR tunnel restriction code shown in Table A; no stopping in a populated area is part of the carrier’s operating procedure for this class.

Stabilization is the load parameter most frequently misunderstood by logistics control towers. Acrylonitrile is exothermically polymerizable, and the transport entry is valid only for inhibited material. Commercial acrylonitrile is commonly inhibited with monomethyl ether of hydroquinone, often abbreviated MEHQ, at 35–50 ppm, and dissolved oxygen can act as a co-inhibitor in the stabilizer system. If the oxygen concentration in the ullage is depleted or the package is repeatedly opened, the inhibition balance can shift. Radical polymerization releases roughly 76 kJ mol⁻¹ of monomer; once the temperature rises above the recommended storage threshold, the exotherm can accelerate and generate pressure inside a sealed drum or IBC. The carrier has no real-time chemical sensor for MEHQ concentration, so the shipper must provide a stabilizer certificate and a re-test date for long-stowage shipments. A stabilized substance that has lost its stabilizer is no longer in conformance with the UN 1093 entry and must not be offered for transport under that description. Published data for the exact time-to-failure in a sealed 20 ft freight container at 40 °C is limited; therefore the conservative operational boundary is to reject any container showing wall deformation, external odor, or sustained self-heating.

Tank cleaning and previous-load compatibility are not optional for this product. The material is a strong solvent and can attack rubber hoses, gaskets, and pump seals. Fluoropolymer-lined hoses and PTFE envelope gaskets are used at loading racks where extended contact is expected. Stainless steel, type 316 or 316L, is the common tank metallurgy, but the cleaning procedure must remove chlorides and hydrocarbon residues. A final drying step is used after water washing. Because dissolved oxygen can act as a co-inhibitor, inerting with nitrogen may remove a stabilization factor; the shipper must confirm that the MEHQ concentration is adequate for the intended oxygen level. The cleaning certificate states the previous cargoes and the method used to measure residue; a tank with an unverified previous load is not to be loaded with acrylonitrile. This is field-level practice at production-scale terminals where batch-to-batch variance in stabilizer concentration must be controlled within the shipper’s certified range.

The solvent strength of acrylonitrile is often underestimated in carrier safety briefings. It swells many elastomer compounds and can extract plasticizers from polyethylene liners if the liner grade is not fluorinated. At a production-scale drum-filling line, a nitrile rubber gasket may pass a water hydro test but fail after continuous vapor contact; therefore PTFE-lined caps and fluoropolymer gaskets are specified. Hoses at loading racks are assigned to acrylonitrile service only, with a maximum service pressure that includes the vapor pressure at the upper route temperature. A hose that has been used for an amine product must not be cross-connected unless it has been decontaminated and the wash-water pH has been verified. The same rule applies to pumps and flow meters; mechanical seals are preferred over packing glands because a small packing leak creates a fire and inhalation hazard at the loading point.

When stabilization failure shifts the risk profile inside a closed freight container

When stabilization failure occurs inside a closed freight container, the first observable indications may be a warm container roof, a sweet or pungent odor at the door gasket, and slight bulging of the container walls. The vapor is heavier than air, with a relative density of 1.83, and accumulates near the floor; door opening must be performed only by responders with gas detection. Gas detection sets a first alarm at 10% LEL because the lower explosive limit is 3.0 vol%; a second alarm is set at the occupational exposure limit of 2 ppm as an 8-hour TWA under OSHA 29 CFR 1910.1045, with a 10 ppm 15-minute excursion limit. The carrier’s role becomes isolation, notification, and provision of the shipping papers and emergency response information under 49 CFR §172.602. Cargo removal is performed only by hazmat-trained personnel wearing positive-pressure self-contained breathing apparatus and chemical-protective clothing with permeation data for acrylonitrile. Direct solid water streams are avoided because they can spread the liquid; water fog is used for vapor knockdown and cooling of fire-exposed containers. Alcohol-resistant foam, dry chemical, or carbon dioxide is used for small fires, with water cooling for adjacent tanks. Runoff retention is required due to aquatic toxicity; the material is subject to marine pollutant requirements where applicable, and containment water must not be discharged to drains.

Documentation set for multimodal acrylonitrile movements

Each modal regime adds a documentation layer without removing the previous one. Under 49 CFR §172.201, the shipping paper identifies the material as UN 1093, Acrylonitrile, stabilized, and includes the hazard class, subsidiary class, packing group, quantity, and the shipper’s certification statement in §172.204. Emergency response information is maintained separately under §172.602 and includes immediate health hazards, fire risks, spill control, and first aid; a safety data sheet alone does not satisfy the emergency response information requirement. For IMDG carriage, the dangerous goods declaration is cut to the IMDG Code 5.4.1 format, and the container packing certificate under 5.4.2 is signed by the person responsible for packing the cargo transport unit. The packing certificate states that the CTU was properly loaded, lashed, and placarded, and that no incompatible cargo was loaded in the same unit. ADR/RID require the instructions in writing in the cab, written in the language of the driver and the countries crossed. IATA air carriage uses the Shipper’s Declaration for Dangerous Goods; for UN 1093 the material is forbidden on passenger aircraft because Packing Group I flammable liquids are not allowed under the IATA Dangerous Goods Regulations, and cargo aircraft quantity limits are set by the applicable packing instruction. The original signed declaration is retained by the air carrier and the shipper for the period specified in the IATA DGR.

Segregation is not only a fire-prevention rule; it is also a food-safety rule because of the Class 6.1 subsidiary. UN 1093 packages are separated from food, feed, and absorbent consumer products in the same cargo transport unit. ADR 7.5.4 and the IMDG Code classify such co-loading as a segregation incompatibility; a plastic pallet wrap is not an acceptable barrier. The carrier checks the container packing certificate and, during door inspection, verifies that no food-grade pallet is stowed next to leakers. For vessel stowage, the flammable-toxic cargo is separated from Class 5.1 oxidizers and Class 8 alkaline substances. Heat sources such as heated bunker tanks and steam lines are identified on the stowage plan and avoided. A PG I liquid in a sealed container still develops a vapor phase; continuous ventilation or on-deck stowage is specified by many vessel operators to disperse any minor flange or valve leakage before it reaches the lower explosive limit. The container door locking bars are secured and the container is not accepted if door gaskets are extruded or the roof shows denting beyond standard ISO damage tolerance.

Before a packaged-goods container is sealed, the carrier or packer checks the internal load plan for segregation violations. Acrylonitrile drums are placed on one side of the container, not mixed with oxidizing or food-grade cargo. Each drum is restrained with rated lashing straps and dunnage that does not trap vapor. The packer closes all drum bungs with a torque wrench to the value specified by the closure manufacturer; a hand-tight bung is not an acceptable closure for PG I flammable-toxic liquid. The container floor is inspected for previous leaks, and a polyethylene liner is used only if the liner is compatible and cannot be degraded by acrylonitrile. The container packing certificate records these actions. A carrier that receives a pre-packed container without a packing certificate must not move it as a sealed load; it is treated as an unverified cargo transport unit.

Limited quantity and excepted quantity relief is generally unavailable for this entry because Packing Group I substances are excluded from the lowest-quantity transport relaxations in ADR Chapter 3.4 and Chapter 3.5. A UN 1093 shipment in a small bottle still triggers the full label set, the shipper’s declaration, and the packaging specification unless a competent modal exception is explicitly allowed. Carriers that treat the material as an ordinary flammable liquid miss the Class 6.1 obligations, including segregation from foodstuffs and the need for toxic-by-inhalation emergency response data. This is an operational boundary and is verified at package level during the acceptance check.

Ocean carriers require the dangerous goods declaration to show the flash point and the packing group, not just Class 3. The flash point is often reported as below 23 °C, which triggers the vessel requirement for electrical equipment in adjacent holds to match flammable vapor classification. For a tank container stowed below deck, the hold ventilation rate is a design parameter; if natural ventilation is insufficient, mechanical exhaust may be set to maintain the vapor concentration below 10% LEL. The vessel stowage plan must separate the tank from living quarters, machinery spaces, and ignition sources. A container with a leaking valve or weeping gasket is not allowed to remain in the general cargo hold; it is isolated on deck or moved to a safe landing area. These rules are enforced through the container inspection before loading and the mate’s receipt remarks.

Air carriage adds a pressure-differential requirement for closures. Packages that are leakproof at ground level can fail at reduced pressure if the closure or inner liner has not been tested for altitude pressure changes. The shipper must use packaging that meets the IATA packing instruction for the PG I flammable-toxic entry; the carrier verifies that the packaging method is stated on the declaration. The external package is labeled with the Class 3 and Class 6.1 labels, and the shipper must comply with the operator’s dangerous goods acceptance check. Because of the toxic subsidiary, passenger aircraft transport is forbidden under the IATA DGR, and cargo aircraft quantities are limited to the net quantity shown in the packing instruction. The operator retains the document and provides it to the pilot-in-command before departure.

Carrier personnel who classify, package, load, or inspect UN 1093 must complete function-specific dangerous goods training and security awareness training. Under ADR Chapter 8.2 and 49 CFR Part 172 Subpart H, training records must include the person’s name, the date of training, and the subject matter; third-party online training alone is not sufficient for a hazmat security plan role. The shipper’s 49 CFR §172.704 training includes general awareness, function-specific, safety, and security awareness. Drivers receive ADR training and must carry the certificate during road movement. A warehouse that only cross-docks the material still requires dangerous goods awareness training for forklift and inspection staff because the label set signals restricted stowage and segregation duties. This is a carrier rule often missed when non-hazmat contracts are used for last-mile delivery.

For a spill or leak during road carriage, the driver isolates the area, shuts down the engine, removes ignition sources, and contacts the emergency response number shown on the shipping paper. The material’s vapor density of 1.83 makes low-lying areas, drains, and pits higher-risk zones. Water contamination from firefighting must be contained. Alcohol-resistant foam or carbon dioxide is used for small fires; water fog is used only to cool closed containers and to knock down vapor, not to extinguish a pool fire. The carrier’s emergency response information must state the exact spill containment method and the initial isolation distance; published ERG isolation distances are reference values, not substitutes for air monitoring. Each UN 1093 package is treated as a closed system until the stabilizer certificate, the label set, and the transport document are complete.