Part VIII, Subpart iii, Chapter 3, Section ADeveloping Claims for Service Connection (SC) for Disabilities Resulting From Exposure to Mustard Gas or Lewisite

Revised April 13, 2026

VIII.iii.3.A.1.a#SC Based on Full-Body Exposure to Mustard Gas or Lewisite During Military Service

38 CFR 3.316 authorizes service connection (SC) for certain diseases diagnosed in Veterans who underwent full-body exposure to mustard gas or Lewisite during military service. Full-body exposure means that the entire body was exposed to mustard agents or Lewisite as opposed to placement of drops of mustard agent or Lewisite on one or more locations on the skin. Mustard gas refers to either of two vesicants (blister-producing agents), sulfur mustard (Yperite) or nitrogen mustard. Lewisite is a mustard vesicant containing arsenic.Reference: For more information on non-presumptive claims due to toxic exposure risk activity (TERA), such as full-body mustard gas or Lewisite exposure, see the Sergeant First Class Heath Robinson Honoring our Promise to Address Comprehensive Toxics (PACT) Act of 2022 Implementation Standard Operating Procedure (SOP).

VIII.iii.3.A.1.b#Veterans Who May Have Been Exposed to Mustard Gas or Lewisite

Veterans who may have been exposed to mustard gas or Lewisite include those who

• were exposed
  • under battlefield conditions in World War I, or
  • during World War II (WWII) as described in M21-1, Part VIII, Subpart iii, 3.A.5
• engaged in the manufacturing, handling, or destruction of vesicant agents during military service, or
• have documented mustard gas or Lewisite exposure in the Individual Longitudinal Exposure Record (ILER) or military records.

Note: Participation in mustard agent and Lewisite testing can be considered a stressor in determining SC for posttraumatic stress disorder (PTSD).References: For more information on

• the destruction of chemical weapons, see
  • 50 U.S.C. 1521, and
  • the Center for Disease Control Chemical Weapons Elimination site, and
• processing claims for PTSD, see M21-1, Part VIII, Subpart iv, 1.

VIII.iii.3.A.1.c#Action to Take When the Veteran Claims Exposure but Does Not Claim a Disability

A claim is not substantially complete if a Veteran alleges exposure to mustard gas or Lewisite during service but does not claim SC for a specific disability. In cases such as these, follow the procedures for handling an incomplete application at M21-1, Part II, Subpart iii, 1.C.2.b and c.Reference: For more information on what constitutes a substantially complete application, see

• 38 CFR 3.159(a)(3), and
• M21-1, Part I, Subpart i, 1.A.4.f.

2Centralized Processing of Claims Based on the Effects of Exposure to Mustard Gas or Lewisite

This topic contains information on the centralized processing of claims based on the effects of exposure to mustard gas or Lewisite, including

• centralized processing of claims and legacy appeals at the Muskogee Regional Office (RO), and
• forwarding claims and legacy appeals to the Muskogee RO.

Revised April 13, 2026

VIII.iii.3.A.2.a#Centralized Processing of Claims and Legacy Appeals at the Muskogee RO

All claims and legacy appeals based on exposure to mustard gas or Lewisite received on or after January 19, 2005, are centrally processed at the Muskogee Regional Office (RO).Exception: In cases involving more than one special mission claim type, the National Work Queue (NWQ) routing rules may route the claim to the RO with jurisdiction of the other special mission claim type.

VIII.iii.3.A.2.b#Forwarding Claims and Legacy Appeals to the Muskogee RO

To route claims and legacy appeals based on exposure to mustard gas or Lewisite to the Muskogee RO, ensure the Mustard Gas special issue indicator is affixed to the relevant contention(s).Note : If a mustard gas claim is already under the jurisdiction of the Muskogee RO and a subsequent claim is received, the Muskogee RO will process the subsequent claim.Reference: For more information on priority processing, see M21-1, Part X, Subpart i, 1.

3Developing Claims Based on the Effects of Exposure to Mustard Gas or Lewisite

This topic contains information on developing claims based on the effects of exposure to mustard gas or Lewisite, including

• tracking mustard gas claims
• developing to the claimant in mustard gas claims, and
• when development for evidence of full-body exposure is necessary.

Revised April 13, 2026

VIII.iii.3.A.3.a#Tracking Mustard Gas Claims

All claims for SC for disabilities resulting from exposure to mustard agents or Lewisite are controlled with

• a standard compensation end product (EP), and
• the Mustard Gas special issue indicator on the relevant contention(s).

Note: Affixing this special issue indicator triggers assignment of the claim to the Muskogee RO.References: For more information on

• centralized processing of mustard gas claims, see M21-1, Part VIII, Subpart iii, 3.A.2
• EP codes, see M21-4, Appendix B, and
• the Veterans Benefits Management System (VBMS), see VBMS Core User Guide.

VIII.iii.3.A.3.b#Developing to the Claimant in Mustard Gas Claims

If the Veteran files a substantially complete claim for SC for a disability due to mustard gas or Lewisite exposure, then send a subsequent development letter with the VBMS development paragraph MG-circumstances of exposure.Exception: Do not send a development letter if the evidence of record

• provides the information the subsequent development letter solicits, or
• is otherwise sufficient to decide the claim.

Important: Claims processors may contact a claimant by telephone to obtain the details about the circumstances of the Veteran’s mustard gas exposure.References: For more information on

• the duty to notice under 38 U.S.C. 5103, see M21-1, Part III, Subpart i, 2.B
• procedures for verifying mustard gas and Lewisite exposure, see M21-1, Part VIII, Subpart iii, 3.A.4.b
• obtaining and documenting information received from a claimant by telephone, see M21-1, Part III, Subpart i, 2.D.1, and
• processing claims in VBMS, see the VBMS Core User Guide.

VIII.iii.3.A.3.c#When Development for Evidence of Full-Body Exposure Is Necessary

Do not request evidence of full-body exposure to mustard gas or Lewisite unless the Veteran alleges exposure and submits competent lay or medical evidence.Reference : For more information on non-presumptive claims due to TERA, such as full-body mustard gas or Lewisite exposure, see the PACT Act Implementation SOP.

4Establishing Full-Body Mustard Gas and Lewisite Exposure

This topic contains information on establishing full-body mustard gas and Lewisite exposure, including

• verifying full-body mustard gas or Lewisite exposure
• procedure for verifying full-body exposure to mustard gas or Lewisite
• researching exposure in ILER, and
• documenting full-body mustard gas and Lewisite exposure.

Revised April 13, 2026

VIII.iii.3.A.4.a#Verifying Full-Body Mustard Gas or Lewisite Exposure

For Veterans who do not meet the requirements for presumptive exposure as listed in M21-1, Part VIII, Subpart iii, 3.A.5.a, establish any explicit claims of full-body mustard gas and Lewisite exposure on a direct, facts-found basis by following the procedures outlined in M21-1, Part VIII, Subpart iii, 3.A.4.b. In these cases, it is imperative that claims processors consider all evidence of record, including

• ILER entries verifying full-body exposure, and
• service records documenting participation in activities consistent with full-body exposure, such as military duties involving the handling or destruction of vesicant agents during military service _. _

_ _Important:

• Descriptions of activities such as drop, patch, or syringe testing of agents where a relatively small area of the skin is affected are not sufficient to concede full-body exposure.
• Generally, vesicant agent exposure for training purposes, such as during gas chamber exercises, largely ceased following the end of testing programs that ran during WWII.

Reference: For more information on direct, facts-found concessions, see 38 CFR 3.303(a).

VIII.iii.3.A.4.b#Procedure for Verifying Full-Body Exposure to Mustard Gas or Lewisite

Follow the procedures in the table below when verifying a claim of exposure to mustard gas or Lewisite.

VIII.iii.3.A.4.c#Researching Exposure in ILER

ILER is a web-based application that provides the ability to link a Veteran to military exposures and/or deployments. Claims processors at the Muskogee RO must utilize ILER to conduct preliminary research regarding claimed in-service mustard gas-related exposures. Important:

• ILER access should be requested in advance of receipt of a claim based on exposure in order to ensure that claims processing is not unnecessarily delayed.
• If ILER does not contain information about full-body exposure, the Department of Veterans Affairs is prohibited from determining that such exposure did not occur based solely on the ILER report.

References: For more information on

• ILER and how to obtain access, see the ILER Guidance, and
• non-presumptive claims due to TERA, such as full-body mustard gas or Lewisite exposure, see the PACT Act Implementation SOP.

VIII.iii.3.A.4.d#Documenting Full-Body Mustard Gas and Lewisite Exposure

The claims processor must ensure the evidence used to support the determination of full-body mustard gas or Lewisite exposure is uploaded to the Veteran’s claims folder. Edit the subject line of the relevant document(s) used to verify exposure using the following format: mustard gas/Lewisite, pg. [number].Example :Reference : For more information on editing document properties, see the VBMS User Guide.

5Presumptive Full-Body Mustard Gas or Lewisite Exposure During WWII

This topic contains guidance on presumptive full-body mustard gas or Lewisite exposure during WWII, including

• presumptive full-body exposure based on service in a known location during WWII
• confirmed locations where mustard gas or Lewisite was used during WWII
• mustard gas incident at Bari, and
• weighing lay evidence of exposure during WWII.

Revised April 13, 2026

VIII.iii.3.A.5.a#Presumptive Full-Body Exposure Based on Service in a Known Location During WWII

During WWII, service members participated in secret mustard agent and Lewisite tests. Some participated in tests that involved the use of significant concentrations of mustard agents or Lewisite either in chambers or field exercises. Others were exposed to minimal amounts of mustard agents and/or Lewisite via patch and drop tests. All participants swore to keep their participation secret.Extend the presumption of full-body exposure to mustard gas or Lewisite based on service in a known location, if the following conditions are met:

• the Veteran served in one of the locations listed in M21-1, Part VIII, Subpart iii, 3.A.5.b, during the specified time period, and
• in judgement of the decision maker, the Veteran adequately describes an activity that is considered full-body exposure to mustard gas or Lewisite per the guidelines in M21-1, Part VIII, Subpart iii, 3.A.5.d.

Notes:

• Resolve reasonable doubt in favor of the Veteran in accordance with 38 CFR 3.102, when warranted.
• Veterans who participated in mustard gas testing prior to 1968 have been released from vows of secrecy by a March 9, 1993, order of Deputy Defense Secretary William J. Perry. Veterans may discuss the type of agent(s) used, location, and circumstances of exposure, as this information is declassified.

VIII.iii.3.A.5.b#Confirmed Locations Where Mustard Gas or Lewisite Was Used During WWII

The table below provides the known locations where, during the designated time frame testing or other incidents occurred that have the potential for full-body exposure to nitrogen mustard gas, sulfur mustard gas, or Lewisite.Important: Follow the procedures listed in M21-1, Part VIII, Subpart iii, 3.A.4.b to verify exposure.

Reference : For more information on mustard gas and Lewisite exposure during WWII, see

• Public Law 115-48 , and

• the Department of Defense Final Report.

VIII.iii.3.A.5.c#Mustard Gas Incident at Bari

The Bari incident was the result of a German air raid against the harbor of Bari, Italy, on December 2, 1943. Among the twenty ships destroyed was a merchant marine ship carrying sulfur mustard bombs. Those exposed to the sulfur mustard were the only known sulfur mustard combat casualties in WWII.

VIII.iii.3.A.5.d#Weighing Lay Evidence of Exposure During WWII

In order for the presumption of exposure to apply for WWII Veterans who served at the locations during the time frames listed in M21-1, Part VIII, Subpart iii, 3.A.5.b, the claim must include a description of an activity that is considered full-body exposure to mustard gas or Lewisite. Descriptions of activities that would be consistent with full-body exposure include statements that refer to terms such as

• chamber testing
• gas chamber
• field exercises
• chemical warfare research or training
• test clothing, and
• exercises simulating battlefield conditions.

Exception : Description of activities such as drop, patch, or syringe testing of agents where a relatively small area of the skin is affected is not sufficient to concede full-body exposure. Reference : For more information on the procedure for verifying full-body exposure to mustard gas or Lewisite, see M21-1, Part VIII, Subpart iii, 3.A.4.b.