What packing group is my dangerous good?

Formula, assumptions, and limits

Packing group assignment under IMDG Code 42-24 and 49 CFR 173 is a set of threshold tests, one table per class. The calculator runs the table for the class picked, adds the provisions of the chosen rule book that move a result across a threshold, and reports the criterion that decided it.

Formula

Derivation

1. Class 3. IMDG Code 2.3.2.6 gives packing group I at an initial boiling point of 35 °C or less, II at a flash point below 23 °C with the boiling point above 35 °C, and III from 23 °C to 60 °C inclusive.¹ 49 CFR 173.121(a) prints the same table with Fahrenheit equivalents, and TDG 2.19(1) adds “any flash point” to packing group I.^2,5
2. Viscous liquids. Under 2.3.2.2, a packing group II liquid moves to III when its ISO 2431 flow time and flash point fit the table, less than 3% clear solvent separates, it does not meet the 6.1 or 8 criteria and the receptacle holds at most 450 L.
3. Class 6.1. Each route is banded by IMDG 2.6.2.2.4.1; a 4-hour dust or mist LC50 is multiplied by 4 (2.6.2.2.4.2) and a 4-hour vapor LC50 by 2 (2.6.2.2.4.5). A vapor is packing group I when $V \ge 10\,LC_{50}$ with $LC_{50} \le 1{,}000$ mL/m³, II when $V \ge LC_{50}$ with $LC_{50} \le 3{,}000$, III when $V \ge LC_{50}/5$ with $LC_{50} \le 5{,}000$. 49 CFR 173.133(a)(3) takes the highest degree of toxicity across routes.⁶
4. Class 8. IMDG 2.8.3.3 and 49 CFR 173.137 band the exposure time that causes irreversible skin damage, and add packing group III for a corrosion rate over 6.25 mm a year on steel or aluminum at 55 °C. For an untested mixture, the step-wise flow chart of IMDG figure 2.8.4.3 and 49 CFR 173.137(d) is applied in the order written in the formula above.⁷

Assumptions

• The flash point is a closed-cup result on the material in the form shipped. 49 CFR 173.120(c)(2) requires a second test after evaporating 10% of a mixture whose first flash point is above −7 °C, and the lower result is the flash point.³
• The boiling point is the initial boiling point by distillation, ASTM D86, ASTM D1078, ISO 3405, ISO 3924 or ISO 4626 (49 CFR 173.121(a)(2)), not a handbook boiling point.
• The figures are the material’s own. No calculator can tell a single-packing-group entry from an n.o.s. entry; the reader checks the list first.
• For Class 8 mixtures, generic concentration limits only: 1% in the first step and 5% in the others.

Worked example

A solvent blend ships under UN1993, Flammable liquid, n.o.s., which the 49 CFR 172.101 table lists in packing groups I, II and III, so the criteria apply.⁸ Its laboratory report gives a Pensky-Martens closed-cup flash point of 73.0 °F and an initial boiling point of 96 °C by ASTM D86.

• Convert: $T_{fp} = (73.0 - 32) \times 5/9 = 22.78$ °C.
• $T_{ibp} = 96 > 35$, so not packing group I.
• $T_{fp} = 22.78 < 23$, so packing group II.

The flash point is within 2 °C of 23 °C; on a road or rail leg under RID or ADR 2025, 2.3.3.1.4 would require a non-equilibrium result to be confirmed by an equilibrium method, and 49 CFR has no such rule.⁴ Read against the printed “≥73 °F” of 173.121, the same sample would fall in packing group III; at 74.0 °F, 23.33 °C, it is packing group III in every rule book.

A toxic liquid shows how the vapor test runs. With a 1-hour vapor LC50 of 800 mL/m³ and a vapor pressure of 5 kPa at 20 °C, $V = 5 \times 10^6 / 101.3 = 49{,}358$ mL/m³. That is 61.7 times the LC50, above 10 times, and the LC50 is at most 1,000 mL/m³: packing group I. Under 49 CFR it is Hazard Zone B, because Zone A needs $V \ge 500\,LC_{50}$ and an LC50 of 200 mL/m³ or less.

Edge cases and limits

• Exact boundaries. A boiling point of 35.0 °C is packing group I; a flash point of 23.0 °C is III; 60.0 °C is III and still Class 3. 60.1 °C is outside Class 3 by sea.
• Heated liquids. A liquid carried at or above its flash point is Class 3 at any flash point, UN 3256 in packing group III above 60 °C (IMDG 2.3.1.2 and 2.3.2.4). 49 CFR 173.120(a) sets this for bulk packagings at a flash point of 37.8 °C (100 °F) or more.
• No sustained combustion. A liquid with a flash point above 35 °C that passes the sustained combustibility test, has a fire point over 100 °C by ISO 2592, or is a water-miscible solution with more than 90% water by mass, need not be treated as Class 3 under IMDG 2.3.1.3, and is excepted from Class 3 under 49 CFR 173.120(a)(1). RID 2.2.3.1.1, note 1, relies on the sustained combustibility test alone.
• Tear gas substances are packing group II even where the data give III (IMDG 2.6.2.2.4.1); 49 CFR 173.133(a)(4) leaves them to the 172.101 table.
• Corrosive and toxic dust. A Class 8 substance with a dust or mist LC50 in packing group I is placed in 6.1 only if its oral or dermal toxicity is in packing group I or II (note to IMDG 2.6.2.2.4.1).

Regulatory basis

IMDG Code Amendment 42-24, adopted by MSC.556(108) on 23 May 2024, is mandatory from 1 January 2026; chapters 2.3, 2.6 and 2.8 hold the criteria.¹ The US criteria are 49 CFR 173.121, 173.133 and 173.137, read on the eCFR as current to 10 November 2026, with the corrosive mixture method in 173.137(d).^2,6,7 RID 2025 applies from 1 January 2025.⁴ The 450 L viscous limit replaced 30 L in IMDG Amendment 39-18, MSC.442(99) of 24 May 2018.⁹

Common errors

1. Adding a flash point condition to packing group I. The transport criterion is the boiling point alone; “flash point below 23 °C and boiling point at most 35 °C” is GHS Category 1 in OSHA 29 CFR 1910.1200 Appendix B.6.¹² A liquid boiling at 30 °C with a 25 °C flash point is packing group I, not III.
2. Using an open-cup flash point. IMDG 2.3.3.4 says open-cup methods give figures a few degrees higher, and the tables are closed-cup.
3. Rounding the Class 3 limit up. The limit is “not more than 60 °C” (49 CFR 173.120(a)); a cut-off of 60.5 °C classes a 60.3 °C liquid as Class 3 when it is not.
4. Reading a 4-hour LC50 against the 1-hour bands. Multiply a 4-hour dust or mist figure by 4 and a 4-hour vapor figure by 2 first.
5. Reclassing as combustible for a sea leg. 49 CFR 173.120(b)(2) bars it for vessel and aircraft except where other transport is impracticable.

Packing group criteria for Classes 3, 6.1 and 8

The packing group thresholds for Classes 3, 6.1 and 8 are the same numbers in IMDG Code 42-24, 49 CFR 173.121, 173.133 and 173.137, ADR and RID 2025 and the Canadian TDG Regulations. The rule books differ only above a 60 °C flash point, for heated and viscous liquids and in the 49 CFR hazard zones for toxic vapors.^1,2,4,5

Acetone is the reference case for the default input: the NIOSH Pocket Guide gives a flash point of 0 °F (−17.8 °C) and a boiling point of 133 °F (56.1 °C), which the table puts in packing group II, and 49 CFR 172.101 lists UN1090 in packing group II.^10,8

Viscous flammable liquids and the 450 L limit

Under IMDG Code 2.3.2.2, RID 2.2.3.1.4 and 49 CFR 173.121(b), a paint, enamel, lacquer, varnish, adhesive or polish with a flash point below 23 °C ships in packing group III instead of II when its ISO 2431 flow time and flash point meet the table below, less than 3% clear solvent separates, it does not meet the Class 6.1 or Class 8 criteria, and the receptacle holds no more than 450 L. The flow time is measured at 23 °C with a 4 mm jet, or a 6 mm jet once the 4 mm time passes 100 s:

The capacity limit is 450 L per receptacle in IMDG 2.3.2.2, RID 2.2.3.1.4 and 49 CFR 173.121(b), and was 30 L in the IMDG Code until Amendment 39-18.⁹ 49 CFR keeps 30 L for passenger aircraft and 100 L for cargo aircraft; TDG 2.19(3) states no capacity limit. Viscous liquids with a flash point from 23 °C to 60 °C and a 6 mm flow time of 60 s or more (40 s at no more than 60% Class 3 content) can be released from package marking, labeling and testing by IMDG 2.3.2.5, and from RID altogether by RID 2.2.3.1.5, provided they are also not environmentally hazardous (the IMDG Code allows 5 L or less per inner packaging) and hold no more than 20% nitrocellulose with at most 12.6% nitrogen. The calculator notes the release for the 60 s route but does not check those two conditions or the 40 s route.

Flash points above 60 °C

A liquid with a closed-cup flash point above 60 °C is outside Class 3 under the IMDG Code, 49 CFR, ADR and RID and the TDG Regulations, with three exceptions: carriage at or above the flash point, diesel and heating oil under ADR and RID, and the US combustible liquid class.

• By sea under the IMDG Code: not Class 3, unless carried at or above the flash point (UN 3256, packing group III).
• ADR and RID: diesel fuel, gas oil and light heating oil with a flash point above 60 °C and not more than 100 °C are deemed Class 3, UN 1202 (RID 2.2.3.1.1, note 2).⁴
• 49 CFR: a combustible liquid from above 60 °C to below 93 °C (200 °F), 173.120(b)(1). In non-bulk packaging it is outside the regulations unless it is a hazardous substance, hazardous waste or marine pollutant, 173.150(f)(2).^3,11
• TDG: Class 3 ends at 60 °C closed cup, 2.18(1), unless the liquid is at or above its flash point in transport.

Where IMDG, 49 CFR, ADR and TDG differ

For the same flash point, boiling point, LD50 or skin test figures, IMDG Code 42-24, 49 CFR, ADR and RID 2025 and the Canadian TDG Regulations differ on the five points below:

The 49 CFR hazard zones decide the inhalation hazard marking of 172.313 and the shipping paper entry of 172.203(m), not the packing group.⁶

Packing groups for Classes 4.1, 4.2, 4.3 and 5.1, and classes with none

Classes 4.1, 4.2, 4.3 and 5.1 have packing groups too, but they come from laboratory outcomes: burning time and the wetted zone in test N.1 for 4.1, cube tests at 100 °C to 140 °C for 4.2, gas evolution in liters per kilogram, per minute for packing group I and per hour for II and III, for 4.3, and burning against potassium bromate or calcium peroxide reference mixtures for 5.1 solids. No figure on a safety data sheet replaces those tests. Under IMDG Code 2.0.1.3, Classes 1, 2, 5.2, 6.2 and 7, the self-reactive substances of Division 4.1 and articles have no packing group. 49 CFR 172.101(f) excludes only Class 2, Class 7, Division 6.2 and articles other than Class 1, so a US entry for an explosive or an organic peroxide can carry one.^1,8