Flash Point and Packing Group: Water-Based vs Solvent Adhesive

A forwarder quotes your first adhesive shipment in four minutes and books it in an hour. Then it asks one question — "is it DG?" — and everything stops. Not because the answer is hard, but because nobody on your side has it. The supplier says the adhesive is safe. Your purchasing contact reads that as "not dangerous goods". The forwarder needs a UN number, a proper shipping name, a class and a packing group, in that form, in writing, from a document with a laboratory value behind it. Safe and non-regulated are unrelated statements.

For adhesives the whole question usually collapses onto a single measured number: the flash point. Understanding what that number does — and how a supplier can hand you a technically true value that answers the wrong question — is most of what an importer needs to stop a booking from unravelling at the cut-off.

Flash point is the switch, and closed cup is the only reading that counts

Flash point is the lowest temperature at which the vapour above a liquid forms an ignitable mixture with air. For transport purposes it sorts liquids into regulated and unregulated, and then sorts the regulated ones into severity bands.

The dividing line is 60 °C, measured closed cup. A liquid at or below that threshold is a Class 3 flammable liquid. Above it, the liquid is generally not Class 3, though it can still be regulated for another reason entirely.

The trap sits in the words closed cup. Open-cup and closed-cup tests are different physical experiments and they return different numbers for the same liquid — the open-cup value is typically the higher of the two, sometimes by a margin large enough to move a mixture across the 60 °C line on paper. A supplier that reports an open-cup result is not lying; it is answering a different question. When you request a flash point, request the method with it: ISO 1523, ISO 13736, ISO 2719, ASTM D93 or ASTM D3278 are the closed-cup families you are likely to see. A value with no method next to it is not usable evidence, and a competent forwarder will treat it that way.

Once you have a closed-cup value, the packing group follows mechanically:

Two numbers therefore decide the packing group, not one: flash point and initial boiling point. A supplier that gives you the flash point and shrugs at the boiling point has given you two-thirds of a classification.

Three details that decide more shipments than the flash point itself

Water-based does not mean non-regulated. A waterborne surround adhesive with no flash point at all clears Class 3 comfortably. It can still be caught as an environmentally hazardous substance if a biocide, a preservative or a residual monomer in the formulation is toxic to aquatic life above the classification cut-off. That routes it to a Class 9 entry with a marine pollutant mark for sea freight, which is a smaller problem than Class 3 but is emphatically not "general cargo". Ask about aquatic toxicity separately from flammability; they are answered by different sections of the safety data sheet and often by different people at the supplier. And check whether the grade carries a co-solvent that puts a flash point back into the mixture — waterborne is a formulation family, not a guarantee. The production trade-offs of moving a bond to a waterborne grade are a separate matter, covered in the water-based surround adhesive discussion; the freight answer is not automatically the easy one.

Viscous adhesives get a relief that thin solvents do not. The UN Model Regulations contain provisions for viscous flammable liquids that let certain paints, adhesives and similar preparations with a flash point in the upper band be reassigned to a less severe packing group, or in defined circumstances be carried outside the dangerous-goods rules altogether. The tests are a solvent-separation limit and a flow-time measurement through a standard ISO 2431 cup, with conditions on pack size and packaging. This is precisely the provision that makes a thick adhesive shippable when a thin one on the same solvent is not — and it is one that a Chinese exporter's shipping department may not have looked at. If a grade sits just inside Class 3 PG III, ask the question directly, because the freight-cost difference is large and the answer is a laboratory measurement rather than an opinion. Confirm the current wording and limits before relying on it.

The classification is per grade and per pack, not per supplier. A single order can contain a non-regulated water-based surround adhesive, a Class 3 PG III solvent grade, a two-part epoxy where the A side is unregulated and the B hardener is corrosive, and a cyanoacrylate whose activator is flammable while the adhesive itself is not. Buyers routinely ask "is your adhesive dangerous goods" as if the company had one answer. Ask for a line per grade, and ask again for each pack size, because limited-quantity relief turns on inner-packaging volume.

What the forwarder will and will not accept

A forwarder is not being obstructive when it refuses to book on a verbal assurance. It is the party that signs into the carrier's system, and carriers audit. Practically, here is how the answers land:

• Declared non-regulated, with a closed-cup flash point above 60 °C and no other hazard — books as general cargo. The forwarder will still normally want the SDS on file, and increasingly wants a non-DG declaration on letterhead.
• Class 3, PG III, sea freight, full container — routine. IMDG stowage rules apply, the container needs placarding and a dangerous goods note, and there is a booking lead time longer than for general cargo.
• Class 3, PG III or II, LCL consolidation — much harder. Many consolidators refuse DG in shared containers, or accept it only into a designated DG box on a limited sailing schedule. This is where a small first order gets expensive, and where a buyer discovers that LCL versus FCL is a compliance decision and not only a volume one.
• Class 3, PG II, air — restricted, expensive, and sometimes cargo-aircraft only. Booking becomes a separate exercise.
• "The supplier says it is fine" — not accepted anywhere, by anyone.

The limited-quantity route is worth understanding before you need it. Dangerous goods packed in small inner packagings, within volume limits set per UN entry, may travel under the Limited Quantity provisions with reduced documentation and a distinctive LQ diamond mark instead of full hazard labels. A separate and stricter Excepted Quantity route exists for even smaller amounts. Both reduce paperwork; neither removes the underlying classification, and the limits and gross-mass caps differ between sea, road and air. For an adhesive sold in bottles and syringes rather than pails, limited quantities is often the difference between a shippable sample programme and an unshippable one — so ask what pack sizes the supplier can offer against the LQ inner limit for the applicable UN entry, and ask before you agree the pack format.

Why an adhesive supplier without an SDS is a freight problem first

The CMH profile for Aosibo Adhesives records that the dangerous-goods classification with UN number and packing group was not provided at review, alongside the safety data sheet and destination-market registration — so none of them are claimed. It states plainly that the range is regulated cargo, and that the safety data sheets, the dangerous-goods classification and the registration should be settled before a first order is agreed rather than after.

Read in freight terms, that sequencing advice is not caution, it is arithmetic. Compliance failures surface at the border, weeks after the money moved. Classification failures surface at the booking desk, before the money moves — and they surface every single time, on every single shipment, because no forwarder can enter a booking without a class. An adhesive supplier that cannot produce a flash point with a test method attached has not yet failed a customs check. It has failed to make the shipment bookable at all.

The profile also notes that the registered address is a sixth-floor unit rather than a ground-level plant, which is consistent with an office, blending or repacking operation, and that adhesive compounding is normally done in licensed premises. That matters here for a specific reason: the flash point is a property of the compounded mixture, so whoever runs the compounding is the party that either has the test data or can commission it. If the trading contact cannot say who that is, the classification question has no addressee — which is the same problem you meet when working out whether you are dealing with a blender or a compounder.

Common questions

Can I classify the adhesive myself from the SDS?

You can read section 14 of the SDS, which should state the UN number, proper shipping name, class, packing group and any marine pollutant status, and section 9, which should carry the flash point and boiling point. What you cannot do is invent those values where the sheet is blank or where section 14 says "not classified" with no supporting flash point in section 9. As the shipper of record you carry responsibility for the declaration, so a sheet with a hole in it is a hole in your liability cover, not the supplier's.

The supplier says the adhesive is non-hazardous. Is that enough for the forwarder?

No, and the wording is the giveaway. "Non-hazardous" is a health-and-environment statement under labelling law; "not subject to the dangerous goods regulations" is a transport statement. Ask for the second sentence in writing, per grade, with the closed-cup flash point and method that supports it. Many forwarders will accept a non-DG declaration on the supplier's letterhead that says exactly that; almost none will accept a marketing assurance.

Does the classification change my HS code or my duty?

No. Transport classification and customs classification are independent systems that happen to describe the same drum. Your HS heading turns on the polymer base and the packing, not on the flash point — which is why the 3506 versus 3208 question is answered separately from this one. Dangerous-goods status does affect your landed cost, though, through freight surcharges, packaging, documentation fees and slower consolidation options.

What to ask the supplier next

Put this in the enquiry alongside the technical questions, and treat unanswered items as unresolved rather than as good news:

1. Per grade, give the closed-cup flash point and the test method and standard number used to measure it.
2. Give the initial boiling point for any grade with a flash point at or below 60 °C.
3. State the UN number, proper shipping name, class, packing group and subsidiary risk for each grade, or state in writing that the grade is not subject to the dangerous goods regulations.
4. State the aquatic toxicity classification and whether the grade is a marine pollutant, separately from the flammability answer.
5. Confirm whether any viscous-liquid relief has been assessed for the solvent-borne grades, and provide the flow-time and solvent-separation results if so.
6. List the pack sizes offered per grade, with net contents, so limited-quantity eligibility can be checked against the inner-packaging limit.
7. Confirm whether packaging supplied is UN-specification, and provide the packaging mark and test certificate reference if it is.
8. Confirm who signs the dangerous goods declaration for the export leg, and whether that person holds current dangerous-goods training.
9. Ask which of the eight stated markets — the United States, Canada, the United Kingdom, Germany, France, the Netherlands, Indonesia and the UAE — the grade has previously shipped to as declared dangerous goods, and ask for the shipping documents from one of those consignments.

Items 1 and 9 do the work. A flash point with ISO 13736 written next to it, and a past declaration with a real UN number on it, tell you that somebody at the supplier has been through a carrier audit. A range of adhesives with no measured flash point anywhere in the file tells you that the freight conversation has not started yet — and that it will start on your side, at your cost, at the point where you were expecting to book. Read it against the SDS and CLP obligations that land on you as the importer, and against the broader import compliance requirements for regulated goods.