HazMat Tool — substance information
Reference only — not a shipping paper, placard mandate, or CVI record.
Nitrogen trioxide
HMT 15 June 2026- UN / ID
- UN 2421
- Hazard class
- 2.3
- Packing group
- —
- ERG guide
- ERG 124
- Special provisions
- SP 1
- Source
- 49 CFR §172 (15 June 2026)
Nitrogen trioxide
Nitrogen trioxide or nitrate radical is an oxide of nitrogen with formula NO3, consisting of three oxygen atoms covalently bound to a nitrogen atom. This highly unstable blue compound has not been isolated in pure form, but can be generated and observed as a short-lived component of gas, liquid, or solid systems. Like nitrogen dioxide NO2, it is a radical (a molecule with an unpaired valence electron), which makes it paramagnetic. It is the uncharged counterpart of the nitrate anion NO−3 and an isomer of the peroxynitrite radical OONO Wikipedia
| Emergency Response Guide No. 124 |
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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(7) Special Provisions (§172.102)
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| 1 |
|---|
(8) Packing Authorizations (§173.***) 
| (8A) Exceptions | None | |
|---|---|---|
| (8B) Non-bulk | 336 | see 49 CFR §173.336 |
| (8C) Bulk | 245 | see 49 CFR §173.245 |
(9) Quantity Limits 
| (9A) Passenger aircraft/rail | Forbidden |
|---|---|
| (9B) Cargo aircraft only | Forbidden |
(10) Vessel stowage 
| (10A) Location | |
|---|---|
| (10B) Other |
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.
Note: In this segregation and separation chart are HazMat of hazard class 2.3 considered depending on their poisonousness by inhalation (Hazard zone A). See special provision 1 and PHMSA Interpretation #09-0252.
| 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 ![]() | ||||||||||||||||||
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1.5 ![]() | ||||||||||||||||||
1.6 ![]() | ||||||||||||||||||
2.1 ![]() | ||||||||||||||||||
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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. |