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Methyl mercaptan

HMT 15 June 2026

UN / ID: UN 1064
Hazard class: 2.3
Packing group: — (multiple — see tabs)
ERG guide: ERG 117
Special provisions: SP 3, SP B7, SP B9, SP B14, SP N89, SP T50
Source: 49 CFR §172 (15 June 2026)

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Methyl mercaptan

Substance Data

Source: PubChem (HSDB, 03.12.2019)

CAS-Number

74-93-1

Flash Point

—

Boiling Point

—

Emergency Response Guide No. 117

Hazardous Materials Table

Source: 49 CFR §172 (15 June 2026)

Packing group
Packing group
Packing group

(3) Hazard class

2.3
Poisonous gas

(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.

3	This material is poisonous by inhalation (see § 171.8 of this subchapter) in Hazard Zone C (see § 173.116(a) of this subchapter), and must be described as an inhalation hazard under the provisions of this subchapter. Browse special provision 3
B7	Safety relief devices are not authorized on multi-unit tank car tanks. Openings for safety relief devices on multi-unit tank car tanks shall be plugged or blank flanged. Browse special provision B7
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
N89	When steel UN pressure receptacles are used, only those bearing the “H” mark are authorized. Browse special provision N89
T50	When portable tank instruction T50 is indicated in Column (7) of the § 172.101 Hazardous Materials Table, the applicable liquefied compressed gas and chemical under pressure descriptions are authorized to be transported in portable tanks in accordance with the requirements of § 173.313 of this subchapter. Browse special provision T50

(8) Packing Authorizations (§173.***)

(8A) Exceptions	None
(8B) Non-bulk	304	see 49 CFR §173.304
(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

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

Source: 49 CFR §176.84

(3) Hazard class

3
Flammable liquids

(4) Identification number

UN 2363

(5) Packing Group

Comparison View of PG

(6) Labels

Cargo Aircraft Only (Cargo Aircraft Only)

(7) Special Provisions (§172.102)

T11

Minimum test pressure (bar)	6
Minimum shell thickness	§ 178.274(d)(2)
Pressure-relief requirements	Normal
Bottom opening requirements	§ 178.275(d)(3)

Browse special provision T11

TP2

a. The maximum degree of filling must not exceed the degree of filling determined by the following:
TP2a

Where:
t_r is the maximum mean bulk temperature during transport,
t_f is the temperature in degrees celsius of the liquid during filling, and
α is the mean coefficient of cubical expansion of the liquid between the mean temperature of the liquid during filling (t_f) and the maximum mean bulk temperature during transportation (t_r) both in degrees celsius.
b. For liquids transported under ambient conditions α may be calculated using the formula:
TP2b

Where:
d₁₅ and d₅₀ are the densities (in units of mass per unit volume) of the liquid at 15 °C (59 °F) and 50 °C (122 °F), respectively.

Browse special provision TP2

TP13

Self-contained breathing apparatus must be provided when this hazardous material is transported by sea.

Browse special provision TP13

(8) Packing Authorizations (§173.***)

(8A) Exceptions	None
(8B) Non-bulk	201	see 49 CFR §173.201
(8C) Bulk	243	see 49 CFR §173.243

(9) Quantity Limits

(9A) Passenger aircraft/rail	Forbidden
(9B) Cargo aircraft only	30 L

(10) Vessel stowage

(10A) Location

Stowage category “E” means the material may be stowed “on deck” or “under deck” 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 is prohibited from carriage on a passenger vessel in which the limiting number of passengers is exceeded.

Source: 49 CFR §172.101(k)

(10B) Other

95	see 49 CFR §176.84
102	see 49 CFR §176.84

Source: 49 CFR §176.84

(3) Hazard class

6.1
Poisonous Material

(4) Identification number

UN 1670

(5) Packing Group

Comparison View of PG

(6) Labels

(7) Special Provisions (§172.102)

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

Browse special provision 2

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

B32

MC 312, MC 330, MC 331, DOT 412 cargo tanks and DOT 51 portable tanks must be made of stainless steel, except that steel other than stainless steel may be used in accordance with the provisions of § 173.24b(b) of this subchapter. Thickness of stainless steel for tank shell and heads for cargo tanks and portable tanks must be the greater of 6.35 mm (0.250 inch) or the thickness required for a tank with a design pressure at least equal to 1.3 times the vapor pressure of the lading at 46 °C (115 °F). In addition, MC 312 and DOT 412 cargo tank motor vehicles must:
a. Be ASME Code (U) stamped for 100% radiography of all pressure-retaining welds;
b. Have accident damage protection which conforms with § 178.345-8 of this subchapter;
c. Have a MAWP or design pressure of at least 87 psig; and
d. Have a bolted manway cover.

Browse special provision B32

N34

Aluminum construction materials are not authorized for any part of a packaging which is normally in contact with the hazardous material.

Browse special provision N34

T20

Minimum test pressure (bar)	10
Minimum shell thickness	8 mm
Pressure-relief requirements	§ 178.275(g)(3)
Bottom opening requirements	Prohibited

Browse special provision T20

TP2

a. The maximum degree of filling must not exceed the degree of filling determined by the following:
TP2a

Where:
d₁₅ and d₅₀ are the densities (in units of mass per unit volume) of the liquid at 15 °C (59 °F) and 50 °C (122 °F), respectively.

Browse special provision TP2

TP13

Self-contained breathing apparatus must be provided when this hazardous material is transported by sea.

Browse special provision TP13

TP38

Each portable 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 may not promote corrosion to steel when wet.

Browse special provision TP38

TP45

Each portable tank must be made of stainless steel, except that steel other than stainless steel may be used in accordance with the provisions of 173.24b(b) of this subchapter. Thickness of stainless steel for portable tank shells and heads must be the greater of 6.35 mm (0.250 inch) or the thickness required for a portable tank with a design pressure at least equal to 1.3 times the vapor pressure of the hazardous material at 46 °C (115 °F).

Browse special provision TP45

(8) Packing Authorizations (§173.***)

(8A) Exceptions	None
(8B) Non-bulk	227	see 49 CFR §173.227
(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

Source: 49 CFR §172.101(k)

(10B) Other

40	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 —	PG I	PG I
1
2	Methyl mercaptan	Ethyl mercaptan	Perchloromethyl mercaptan
3	2.3	3	6.1
4	UN 1064	UN 2363	UN 1670
5	—	I	I
6	2.3, 2.1	3	6.1
7	3, B7, B9, B14, N89, T50	T11, TP2, TP13	2, B9, B14, B32, N34, T20, TP2, TP13, TP38, TP45
8A	None	None	None
8B	304	201	227
8C	314, 315	243	244
9A	Forbidden	Forbidden	Forbidden
9B	Forbidden	30 L	Forbidden
10A	D	E	D
10B	40	95, 102	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.

Note: The HMR prohibit only those Division 6.1 liquids that meet the definition of a Packing Group (PG) I and Hazard Zone A. See special provision 1 and PHMSA Interpretation #09-0252.

Packages with POISON or POISON INHALATION HAZARD labels, or a POISON label displaying “PG III,” or “PG III” marked next to a POISON label may not be transported with foodstuffs, feed or any other edible material, intended for humans or animals. For exceptions see 49 CFR §177.841(e).

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 1873	Perchloric acid with more than 50 percent but not more than 72 percent acid, by mass	5.1
UN 1802	Perchloric acid with not more than 50 percent acid by mass	8
	Perchloric acid, with more than 72 percent acid by mass	Forbidden
UN 3211	Perchlorates, inorganic, aqueous solution, n.o.s.	5.1
UN 1447	Barium perchlorate, solid	5.1
UN 3406	Barium perchlorate, solution	5.1
	Diazonium perchlorates (dry)	Forbidden
	Ethylene diamine diperchlorate	Forbidden
UN 1470	Lead perchlorate, solid	5.1
UN 3408	Lead perchlorate, solution	5.1
	m-Nitrobenzene diazonium perchlorate	Forbidden
	m-Phenylene diaminediperchlorate (dry)	Forbidden
	Methylamine perchlorate (dry)	Forbidden
UN 1481	Perchlorates, inorganic, n.o.s.	5.1
	Tetraethylammonium perchlorate (dry)	Forbidden