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Compressed gas, toxic, oxdizing, corrosive, n.o.s. Inhalation Hazard Zone A

HMT May 2026

UN / ID: UN 3306
Hazard class: 2.3
Packing group: n/a (multiple — see tabs)
ERG guide: ERG 124
Special provisions: SP 1
Source: 49 CFR §172 (2026/05)

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Compressed gas, toxic, oxdizing, corrosive, n.o.s. Inhalation Hazard Zone A

Emergency Response Guide No. 124

Hazardous Materials Table

Source: 49 CFR §172 (2026/05)

Packing group
Packing group
Packing group

(3) Hazard Class

2.3
Poisonous gas

This entry is signed with "G". The letter "G" identifies proper shipping names for which one or more technical names of the hazardous material must be entered in parentheses, in association with the basic description. (See §172.203(k)).
This entry is signed with "I". The letter "I" identifies proper shipping names which are appropriate for describing materials in international transportation. An alternate proper shipping name may be selected when only domestic transportation is involved.

(7) Special Provisions (§172.102)

×Note:
Special provisions may be very complex. The extracts are taken from 49 CFR §172.102. Please be careful with the information, as necessary, additional conditions may be applied that are not written here. Please check the original source and report bugs.

1	This material is poisonous by inhalation (see §171.8) in Hazard Zone A (see §173.116 or §173.133), and must be described as an inhalation hazard under the provisions of this subchapter. Browse special provision 1

(8) Packing Authorizations (§173.***)

(8A) Exceptions	None
(8B) Non-bulk	192	see 49 CFR §173.192
(8C) Bulk	244	see 49 CFR §173.244

(9) Quantity Limits

(9A) Passenger aircraft/rail	Forbidden
(9B) Cargo aircraft only	Forbidden

(10) Vessel stowage

(10A) Location

Stowage category “D” means the material must be stowed “on deck only” on a cargo vessel or on a passenger vessel carrying a number of passengers limited to not more than the larger of 25 passengers or one passenger per each 3 m of overall vessel length, but the material is prohibited on a passenger vessel in which the limiting number of passengers is exceeded.

Source: 49 CFR §172.101(k)

(10B) Other

40	see 49 CFR §176.84
89	see 49 CFR §176.84
90	see 49 CFR §176.84

Source: 49 CFR §176.84

(3) Hazard Class

2.3
Poisonous gas

(4) Identification number

UN 3306

(5) Packing Group

n/a

Comparison View of PG

(6) Labels

(1) Symbols

(7) Special Provisions (§172.102)

2	This material is poisonous by inhalation (see §171.8) in Hazard Zone B (see §173.116 or §173.133), and must be described as an inhalation hazard under the provisions of this subchapter. Browse special provision 2
B9	Bottom outlets are not authorized. Browse special provision B9
B14	Each bulk packaging, except a tank car or a multi-unit-tank car tank, must be insulated with an insulating material so that the overall thermal conductance at 15.5 °C (60 °F) is no more than 1.5333 kilojoules per hour per square meter per degree Celsius (0.075 Btu per hour per square foot per degree Fahrenheit) temperature differential. Insulating materials must not promote corrosion to steel when wet. Browse special provision B14

(8) Packing Authorizations (§173.***)

(8A) Exceptions	None
(8B) Non-bulk	302, 305	see 49 CFR §173.302, 305
(8C) Bulk	314, 315	see 49 CFR §173.314, 315

(9) Quantity Limits

(9A) Passenger aircraft/rail	Forbidden
(9B) Cargo aircraft only	Forbidden

(10) Vessel stowage

(10A) Location

Source: 49 CFR §172.101(k)

(10B) Other

40	see 49 CFR §176.84
89	see 49 CFR §176.84
90	see 49 CFR §176.84

Source: 49 CFR §176.84

(3) Hazard Class

2.3
Poisonous gas

(4) Identification number

UN 3306

(5) Packing Group

n/a

Comparison View of PG

(6) Labels

(1) Symbols

(7) Special Provisions (§172.102)

3	This material is poisonous by inhalation (see §171.8) in Hazard Zone C (see §173.116), and must be described as an inhalation hazard under the provisions of this subchapter. Browse special provision 3
B14	Each bulk packaging, except a tank car or a multi-unit-tank car tank, must be insulated with an insulating material so that the overall thermal conductance at 15.5 °C (60 °F) is no more than 1.5333 kilojoules per hour per square meter per degree Celsius (0.075 Btu per hour per square foot per degree Fahrenheit) temperature differential. Insulating materials must not promote corrosion to steel when wet. Browse special provision B14

(8) Packing Authorizations (§173.***)

(8A) Exceptions	None
(8B) Non-bulk	302, 305	see 49 CFR §173.302, 305
(8C) Bulk	314, 315	see 49 CFR §173.314, 315

(9) Quantity Limits

(9A) Passenger aircraft/rail	Forbidden
(9B) Cargo aircraft only	Forbidden

(10) Vessel stowage

(10A) Location

Source: 49 CFR §172.101(k)

(10B) Other

40	see 49 CFR §176.84
89	see 49 CFR §176.84
90	see 49 CFR §176.84

Source: 49 CFR §176.84

(3) Hazard Class

2.3
Poisonous gas

(4) Identification number

UN 3306

(5) Packing Group

n/a

Comparison View of PG

(6) Labels

(1) Symbols

(7) Special Provisions (§172.102)

4	This material is poisonous by inhalation (see §171.8) in Hazard Zone D (see §173.116), and must be described as an inhalation hazard under the provisions of this subchapter. Browse special provision 4

(8) Packing Authorizations (§173.***)

(8A) Exceptions	None
(8B) Non-bulk	302, 305	see 49 CFR §173.302, 305
(8C) Bulk	314, 315	see 49 CFR §173.314, 315

(9) Quantity Limits

(9A) Passenger aircraft/rail	Forbidden
(9B) Cargo aircraft only	Forbidden

(10) Vessel stowage

(10A) Location

Source: 49 CFR §172.101(k)

(10B) Other

40	see 49 CFR §176.84
89	see 49 CFR §176.84
90	see 49 CFR §176.84

Source: 49 CFR §176.84

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 n/a	PG n/a	PG n/a	PG n/a
1	G I	G I	G I	G I
2	Compressed gas, toxic, oxdizing, corrosive, n.o.s. Inhalation Hazard Zone A	Compressed gas, toxic, oxidizing, corrosive, n.o.s. Inhalation Hazard Zone B	Compressed gas, toxic, oxidizing, corrosive, n.o.s. Inhalation Hazard Zone C	Compressed gas, toxic, oxidizing, corrosive, n.o.s. Inhalation Hazard Zone D
3	2.3	2.3	2.3	2.3
4	UN 3306	UN 3306	UN 3306	UN 3306
5	n/a	n/a	n/a	n/a
6	2.3, 5.1, 8	2.3, 5.1, 8	2.3, 5.1, 8	2.3, 5.1, 8
7	1	2, B9, B14	3, B14	4
8A	None	None	None	None
8B	192	302, 305	302, 305	302, 305
8C	244	314, 315	314, 315	314, 315
9A	Forbidden	Forbidden	Forbidden	Forbidden
9B	Forbidden	Forbidden	Forbidden	Forbidden
10A	D	D	D	D
10B	40, 89, 90	40, 89, 90	40, 89, 90	40, 89, 90

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/B). See PHMSA Interpretation #09-0252.

Scope & sources (important)Click to show CFR references

This check evaluates segregation per 49 CFR §177.848. Additional loading/unloading and handling requirements may still apply; see 49 CFR §177 Subpart B (Loading and Unloading):

§177.834 - General requirements
§177.835 - Class 1 materials
§177.837 - Class 3 materials
§177.838 - Class 4 (flammable solid) materials, Class 5 (oxidizing) materials, and Division 4.2 (pyroforic liquid) materials
§177.839 - Class 8 (corrosive) materials
§177.840 - Class 2 (gases) materials
§177.841 - Division 6.1 and Division 2.3 materials
§177.842 - Class 7 (radioactive) material
§177.843 - Contamination of vehicles

Similar substances

UN / ID	Proper shipping name	Hazard class
UN 3489	Toxic by inhalation liquid, flammable, corrosive, n.o.s. with an LC50 lower than or equal to 1000 ml/m3 and saturated vapor concentration greater than or equal to 10 LC50	6.1
UN 3488	Toxic by inhalation liquid, flammable, corrosive, n.o.s. with an LC50 lower than or equal to 200 ml/m3 and saturated vapor concentration greater than or equal to 500 LC50	6.1
UN 3390	Toxic by inhalation liquid, corrosive, n.o.s. with an LC50 lower than or equal to 1000 ml/m3 and saturated vapor concentration greater than or equal to 10 LC50	6.1
UN 3389	Toxic by inhalation liquid, corrosive, n.o.s. with an LC50 lower than or equal to 200 ml/m3 and saturated vapor concentration greater than or equal to 500 LC50	6.1
UN 3490	Toxic by inhalation liquid, water-reactive, flammable, n.o.s. with an LC50 lower than or equal to 200 ml/m3 and saturated vapor concentration greater than or equal to 500 LC50	6.1
UN 3388	Toxic by inhalation liquid, oxidizing, n.o.s. with an LC50 lower than or equal to 1000 ml/m3 and saturated vapor concentration greater than or equal to 10 LC50	6.1
UN 3387	Toxic by inhalation liquid, oxidizing, n.o.s. with an LC50 lower than or equal to 200 ml/m3 and saturated vapor concentration greater than or equal to 500 LC50	6.1
UN 3384	Toxic by inhalation liquid, flammable, n.o.s. with an LC50 lower than or equal to 1000 ml/m3 and saturated vapor concentration greater than or equal to 10 LC50	6.1
UN 3383	Toxic by inhalation liquid, flammable, n.o.s. with an LC50 lower than or equal to 200 ml/m3 and saturated vapor concentration greater than or equal to 500 LC50	6.1
UN 3491	Toxic by inhalation liquid, water-reactive, flammable, n.o.s. with an LC50 lower or equal to 1000 ml/m3 and saturated vapor concentration greater than or equal to 10 LC50	6.1
UN 3386	Toxic by inhalation liquid, water-reactive, n.o.s. with an LC50 lower than or equal to 1000 ml/m3 and saturated vapor concentration greater than or equal to 10 LC50	6.1
UN 3385	Toxic by inhalation liquid, water-reactive, n.o.s. with an LC50 lower than or equal to 200 ml/m3 and saturated vapor concentration greater than or equal to 500 LC50	6.1
UN 3382	Toxic by inhalation liquid, n.o.s. with an LC50 lower than or equal to 1000 ml/m3 and saturated vapor concentration greater than or equal to 10 LC50	6.1
UN 3381	Toxic by inhalation liquid, n.o.s. with an LC50 lower than or equal to 200 ml/m3 and saturated vapor concentration greater than or equal to 500 LC50	6.1
UN 3309	Liquefied gas toxic, flammable, corrosive, n.o.s. Inhalation Hazard Zone B	2.3