Tetrahydrofuran (THF, CAS 109-99-9, UN 2056) is a cyclic ether with a closed-cup flash point of -14.5 °C, an initial boiling point of 65.0 °C, a vapor pressure of 19.3 kPa at 20 °C, and a density of 0.889 g/cm³ at 20 °C. The lower explosion limit is 1.8 vol% and the upper explosion limit is 11.8 vol%, which places ordinary vial headspace within the flammable range at ambient temperature. Under 49 CFR 172.101, the Hazardous Materials Table assigns THF to Class 3, Packing Group II, with the proper shipping name “Tetrahydrofuran.” The equivalent entries appear in IATA DGR 4.2, ADR Part 3, and the IMDG Code Part 3. The shipment question is therefore not a routine laboratory consumables decision; it is a dangerous goods compliance decision driven by inner packaging volume, total package mass, closure integrity, and chemical stabilization.

Can a THF Sample Be Shipped? Dangerous Goods Sample Compliance

A THF sample may be transported when the consignor selects the correct quantity regime and packaging system. The smallest regulatory relief path is the excepted quantity, but the volume ceilings are sharply limited. Under 49 CFR 173.4a, a Packing Group II flammable liquid may be shipped as an excepted quantity at 1.0 mL per inner packaging with an aggregate outer package net quantity limit of 500 mL. Under IATA DGR 2.6, excepted quantity code E2 for UN 2056 permits 30 mL per inner packaging and 500 mL net per outer package. The difference between those two regimes is material: a 4 mL or 20 mL vial may fit within the IATA excepted quantity allowance but can exceed the U.S. ground excepted quantity limit for a single inner packaging.

Limited quantity is the next tier. Under ADR 3.4, IMDG Code 3.4, and 49 CFR 173.150, the inner packaging limit is 1.0 L and the package gross mass limit is 30 kg. Under IATA DGR Y341, the same 1.0 L inner limit applies to passenger and cargo aircraft, but the shipper must apply the limited quantity mark and must include the limited quantity notation in the air waybill. Full declared shipment applies when a single inner container exceeds 1.0 L, when the package gross mass exceeds 30 kg, or when the consignee cannot accept a limited quantity or excepted quantity consignment. For full air shipment, IATA DGR 4.2 assigns Packing Instructions 353 for passenger and cargo aircraft and 364 for cargo aircraft only. The maximum net quantity per package for a Packing Group II flammable liquid is 5 L on passenger aircraft and 60 L on cargo-only aircraft.

Small-Quantity Thresholds That Change the Packaging Regime

The following thresholds determine whether a THF sample travels as a full declared Class 3 consignment, a limited quantity package, or an excepted quantity package. The limits apply only after the sample matrix has been correctly classified.

The table should be applied only after the sample matrix is classified. A neat THF sample is UN 2056, but a resin solution in THF may fall under UN 1866, resin solution, Class 3, Packing Group II, depending on flash point and composition. Aqueous THF process samples may exhibit elevated closed-cup flash points, but a shipper cannot self-exempt a flammable liquid without test data or a technical classification reference. Under 49 CFR 173.22, classification must be based on reliable information. For low-viscosity THF, the flash point is commonly determined by ASTM D56 or ASTM D3828; if a sample contains dissolved high-molecular-weight material and viscosity exceeds 5.5 mm²/s at 40 °C, ASTM D93 or another suitable method may be required. Class 3 transport classification applies to liquids with a flash point not more than 60 °C.

When Air Pressure Differentials and Peroxide Chemistry Reset the Sample-Shipment Envelope

Air transport imposes a pressure-differential requirement that is not present in the same form for ground limited quantity packages. Under IATA DGR 5.0.2.4, packages for liquids must be capable of withstanding without leakage an internal pressure differential of not less than 95 kPa. A sealed glass vial containing THF at 20 °C has a vapor pressure of 19.3 kPa, which does not by itself approach the test pressure, but a package in a non-temperature-controlled air cargo container may reach 55 °C or higher. Under ADR 4.1.1.4, liquid inner packagings must have sufficient outage to avoid filling at 55 °C. The required outage is not a fixed percentage for every package; it must be derived from thermal expansion data, but small sample vials are commonly filled below 80% of nominal capacity to provide ullage. A screw-cap vial should be evaluated for closure torque retention and leak rate before package assembly. PTFE-lined closures are required for primary containment because THF attacks natural rubber and many elastomer cap liners.

Peroxide formation is the second technical boundary. THF is a peroxide-forming ether. Bulk THF is normally inhibited with butylated hydroxytoluene at a concentration of 0.025% to 0.035% to suppress radical-chain peroxide accumulation. A partially filled vial exposed to air can accumulate peroxide species over time. No modal regulation sets a universal peroxide concentration for transport; the shipper must assess whether the material has undergone hazardous decomposition. Peroxide concentration is commonly measured by titration using ASTM E298 or an equivalent method. A sample drawn from an uninhibited bulk container or from a process stream with long air exposure should be analyzed before packaging. If peroxides exceed the shipper’s internal acceptance limit, the sample is not transportable without stabilization or further treatment.

Selecting Secondary Containment and Absorbents for Ether Solvent Packages

Primary containment for THF samples should be borosilicate glass with PTFE-lined closures. Low-density polyethylene may be used only as a short-contact secondary pouch; THF permeates and swells many polymers, and rigid polystyrene vials or unlined polypropylene caps are unsuitable. The secondary container must hold an absorbent material sufficient to soak up the entire liquid contents of the inner packaging. Vermiculite or mineral-based sorbents are preferred because cellulosic sorbents add combustible material and can retain flammable vapor. Under IATA DGR 5.0.3.2 and equivalent ADR and 49 CFR provisions, absorbent must be placed between the inner packaging and the outer packaging for liquids. The outer container should be a strong fibreboard box or, for larger full regulated shipments, a UN-specification package bearing the appropriate performance level, such as 4G/X or 4G/Y. The package should be closed with tape that does not degrade on contact with THF vapor; the internal secondary pouch should be heat-sealed.

Full regulated consignments require a dangerous goods declaration or shipping paper. The information must include the consignor and consignee, UN 2056, proper shipping name “Tetrahydrofuran,” Class 3, Packing Group II, net quantity, packing instruction, and, for air shipments, a 24-hour emergency response telephone number under IATA DGR 8.2.3.1. The package must carry the Class 3 hazard label, orientation arrows when required for liquid inner packagings, and the proper shipping name and UN 2056 on the outer package. Limited quantity and excepted quantity packages are not required to carry the full Class 3 label, but they must bear the correct limited quantity or excepted quantity mark. The marks differ in design and are not interchangeable. The limited quantity mark must conform to 49 CFR 172.315, ADR 3.4.7, or IATA DGR 7.1.4.1 as applicable. The Class 3 label, where required, must conform to 49 CFR 172.419 or ADR 5.2.2.2.2.

Personnel who prepare, offer, or sign for THF samples must be trained. Under 49 CFR 172.704, hazardous materials employees require general awareness, function-specific, safety, and security awareness training at least every three years. For air shipments, IATA DGR 1.5 requires recurrent training within 24 months. A supplier Safety Data Sheet completed under 29 CFR 1910.1200 or REACH Annex II may provide classification data, but it is not a substitute for the transport document. Carrier acceptance is separate from regulatory compliance; some express carriers prohibit Class 3 samples in air networks, while others accept limited quantities only under account-specific approval. A consignor must verify the carrier’s dangerous goods operating conditions before first tender because private terms can lawfully exceed the minimum regulatory thresholds. Returning an opened THF sample from a laboratory to a supplier is also a dangerous goods shipment; the original bottle may have been opened, which can change peroxide status and reduce closure integrity, so the return consignor is responsible for classification and repackaging.