Adsorbed gas, toxic, n.o.s. Inhalation hazard zone A
HMT 15 June 2026- UN / ID
- UN 3512
- Hazard class
- 2.3
- Packing group
- — (multiple — see tabs)
- ERG guide
- ERG 173
- Special provisions
- SP 1
- Source
- 49 CFR §172 (15 June 2026)
Adsorbed gas, toxic, n.o.s. Inhalation hazard zone A
Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. This process differs from absorption, in which a fluid (the absorbate) is dissolved by or permeates a liquid or solid (the absorbent). While adsorption does often precede absorption, which involves the transfer of the absorbate into the volume of the absorbent material, alternatively, adsorption is distinctly a surface phenomenon, wherein the adsorbate does not penetrate through the material surface and into the bulk of the adsorbent Wikipedia
| Emergency Response Guide No. 173 |
Hazardous Materials Table
Source: 49 CFR §172 (15 June 2026)(3) Hazard class2.3Poisonous gas |
(4) Identification number |
(5) Packing Group |
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(6) Labels |
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(1) Symbols |
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| 1 |
|---|
(8) Packing Authorizations (§173.***) 
| (8A) Exceptions | None | |
|---|---|---|
| (8B) Non-bulk | 302c | see 49 CFR §173.302c |
| (8C) Bulk | None |
(9) Quantity Limits 
| (9A) Passenger aircraft/rail | Forbidden |
|---|---|
| (9B) Cargo aircraft only | Forbidden |
(10) Vessel stowage 
| (10A) Location | |
|---|---|
| (10B) Other |
(3) Hazard class2.3Poisonous gas |
(4) Identification number |
(5) Packing Group |
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(6) Labels |
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(1) Symbols |
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| 2 | |
|---|---|
| B9 | |
| B14 |
(8) Packing Authorizations (§173.***) 
| (8A) Exceptions | None | |
|---|---|---|
| (8B) Non-bulk | 302c | see 49 CFR §173.302c |
| (8C) Bulk | None |
(9) Quantity Limits 
| (9A) Passenger aircraft/rail | Forbidden |
|---|---|
| (9B) Cargo aircraft only | Forbidden |
(10) Vessel stowage 
| (10A) Location | |
|---|---|
| (10B) Other |
(3) Hazard class2.3Poisonous gas |
(4) Identification number |
(5) Packing Group |
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(6) Labels |
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(1) Symbols |
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| 3 | |
|---|---|
| B14 |
(8) Packing Authorizations (§173.***) 
| (8A) Exceptions | None | |
|---|---|---|
| (8B) Non-bulk | 302c | see 49 CFR §173.302c |
| (8C) Bulk | None |
(9) Quantity Limits 
| (9A) Passenger aircraft/rail | Forbidden |
|---|---|
| (9B) Cargo aircraft only | Forbidden |
(10) Vessel stowage 
| (10A) Location | |
|---|---|
| (10B) Other |
(3) Hazard class2.3Poisonous gas |
(4) Identification number |
(5) Packing Group |
|||||||
(6) Labels |
|||||||||
(1) Symbols |
|||||||||
| 4 |
|---|
(8) Packing Authorizations (§173.***) 
| (8A) Exceptions | None | |
|---|---|---|
| (8B) Non-bulk | 302c | see 49 CFR §173.302c |
| (8C) Bulk | None |
(9) Quantity Limits 
| (9A) Passenger aircraft/rail | Forbidden |
|---|---|
| (9B) Cargo aircraft only | Forbidden |
(10) Vessel stowage 
| (10A) Location | |
|---|---|
| (10B) Other |
Packing group comparison
Multiple packing groups apply to this entry. See assignment criteria in 49 CFR §173 Subpart D. Details are in the tabs above; differences are highlighted.
| PG — | PG — | PG — | PG — | |
|---|---|---|---|---|
| 1 | G | G | G | G |
| 2 | Adsorbed gas, toxic, n.o.s. Inhalation hazard zone A | Adsorbed gas, toxic, n.o.s. Inhalation hazard zone B | Adsorbed gas, toxic, n.o.s. Inhalation hazard zone C | Adsorbed gas, toxic, n.o.s. Inhalation hazard zone D |
| 3 | 2.3 | 2.3 | 2.3 | 2.3 |
| 4 | UN 3512 | UN 3512 | UN 3512 | UN 3512 |
| 5 | — | — | — | — |
| 6 | 2.3 | 2.3 | 2.3 | 2.3 |
| 7 | 1 | 2, B9, B14 | 3, B14 | 4 |
| 8A | None | None | None | None |
| 8B | 302c | 302c | 302c | 302c |
| 8C | None | None | None | None |
| 9A | Forbidden | Forbidden | Forbidden | Forbidden |
| 9B | Forbidden | Forbidden | Forbidden | Forbidden |
| 10A | D | D | D | D |
| 10B | 40 | 40 | 40 | 40 |
Segregation chart for load, transport, and storage
This chart shows whether loading, transport, or storage with other hazard classes is permitted, prohibited, or restricted. Based on 49 CFR §177.848.
| Hazard class | 8![]() | 7![]() | 6.1![]() | 5.2![]() | 5.1![]() | 4.3![]() | 4.2![]() | 4.1![]() | 3![]() | 2.3B![]() | 2.3A![]() | 2.2![]() | 2.1![]() | 1.6![]() | 1.5![]() | 1.4![]() | 1.3![]() | 1.1/1.2![]() |
1.1/1.2 ![]() | ||||||||||||||||||
1.3 ![]() | ||||||||||||||||||
1.4 ![]() | ||||||||||||||||||
1.5 ![]() | ||||||||||||||||||
1.6 ![]() | ||||||||||||||||||
2.1 ![]() | ||||||||||||||||||
2.2 ![]() | ||||||||||||||||||
2.3A ![]() | ||||||||||||||||||
2.3B ![]() | ||||||||||||||||||
3 ![]() | ||||||||||||||||||
4.1 ![]() | ||||||||||||||||||
4.2 ![]() | ||||||||||||||||||
4.3 ![]() | ||||||||||||||||||
5.1 ![]() | ||||||||||||||||||
5.2 ![]() | ||||||||||||||||||
6.1 ![]() | ||||||||||||||||||
7 ![]() | ||||||||||||||||||
8 ![]() |
| Must not be loaded, transported, or stored together in the same vehicle or facility. | |
| May be loaded, transported, or stored together. | |
| May be loaded, transported, or stored together only with restrictions. |