HazMat Tool — substance information

Methyldichloroarsine

HMT May 2026

UN / ID: NA 1556
Hazard class: 6.1
Packing group: I
ERG guide: —
Special provisions: SP 2, SP T20, SP TP4, SP TP13, SP TP38, SP TP45
Source: 49 CFR §172 (2026/05)

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Methyldichloroarsine

Methyldichloroarsine, sometimes abbreviated "MD" and also known as methyl Dick, is an organoarsenic compound with the formula CH3AsCl2. This colourless volatile liquid is a highly toxic vesicant that has been used in chemical warfare. Wikipedia

Hazardous Materials Table

Source: 49 CFR §172 (2026/05)

(3) Hazard Class

6.1
Poisonous Material

(4) Identification number

NA 1556

(5) Packing Group

(6) Labels

(1) Symbols

This entry is signed with "D". The letter "D" identifies proper shipping names which are appropriate for describing materials for domestic transportation but may be inappropriate for international transportation under the provisions of international regulations (e.g., IMO, ICAO). An alternate proper shipping name may be selected when either domestic or international 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.

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

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

TP4

The maximum degree of filling for portable tanks must not exceed 90%.

Browse special provision TP4

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	192	see 49 CFR §173.192
(8C) Bulk	None

(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

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 1698	Diphenylamine chloroarsine	6.1
UN 1699	Diphenylchloroarsine, liquid	6.1
UN 3450	Diphenylchloroarsine, solid	6.1
	Dichlorovinylchloroarsine	Forbidden
UN 1892	Ethyldichloroarsine	6.1