VA M21-1 Update: Mustard Gas and Lewisite Claim Procedures Revised

The Department of Veterans Affairs has updated the section of its M21-1 Adjudication Procedures Manual that governs rating claims for disabilities associated with mustard gas or Lewisite exposure. The revision lives at M21-1, Part VIII, Subpart iii, Chapter 3, Section B (VIII.iii.3.B), and it refreshes the rating procedures VA personnel use when adjudicating these specific chemical warfare agent exposure claims.

If you were exposed to mustard gas or Lewisite during military service — whether through full-body chamber tests, patch tests, production line work, or combat-era handling — this update touches the playbook raters use on your file. It does not change the underlying presumptive framework written in regulation, but it does change how the VA's adjudicators apply that framework. That matters because the manual is what raters actually read when they sit down with your claim.

Here is what the update covers, who should care, and how to position your file so the revised procedures work in your favor.

What the Mustard Gas and Lewisite Rule Means

Mustard gas (sulfur mustard) and Lewisite are chemical warfare agents used and tested by the US military across multiple eras, including World War I, World War II, and later research programs. Veterans were exposed in several documented ways: chamber tests at facilities such as Edgewood Arsenal and the Naval Research Laboratory, patch testing on skin, field exercises, and production or handling duties.

For decades, the VA has recognized that exposure to these agents can cause specific chronic conditions. The presumptive framework — written into VA regulation — allows certain diseases to be service-connected on a presumptive basis if you have a qualifying exposure history and a qualifying current diagnosis. The conditions typically associated with full-body or prolonged exposure include certain respiratory cancers, chronic respiratory diseases such as chronic obstructive pulmonary disease, certain skin cancers and chronic skin conditions in exposed areas, and conjunctivitis-related eye conditions, among others tied to the specific agent and exposure intensity.

The M21-1 manual section at VIII.iii.3.B is the operational guidance that translates this regulation into rater action. It tells the adjudicator how to verify exposure, how to evaluate the medical evidence, how to assign a diagnostic code under the VA Schedule for Rating Disabilities (VASRD), and how to handle claims that fall outside the strict presumptive list but still relate to documented exposure.

What This Update Actually Changes

According to the VA's published guidance, the revision updates the rating procedures used by adjudicators when developing and deciding mustard gas and Lewisite exposure claims. The change sits inside the M21-1 manual at Part VIII, Subpart iii, Chapter 3, Section B.

The M21-1 is procedural rather than regulatory. That distinction is important. Procedural updates of this kind generally clarify rater workflow, refresh references to current VASRD diagnostic codes, align the manual with recent regulatory or policy adjustments, and tighten how exposure verification and medical nexus are documented inside the claim file. They do not, by themselves, expand or contract the list of presumptive conditions — that lives in the Code of Federal Regulations and changes only through formal rulemaking.

For the specific text of the revised section and the effective date of the change, review the VA's change log directly at the VA Changes By Date portal. The change log identifies what was added, removed, or rewritten in this manual section so you can compare the previous procedure to the current one.

What you should take from this: if your mustard gas or Lewisite claim is currently in development, in appeals, or being prepared, the rater handling your file is now applying the updated VIII.iii.3.B procedures. Knowing the current procedure helps you submit evidence in the format and order the rater is trained to process.

Who Should Pay Attention

You should read this update carefully if any of the following describes your service or your claim:

• You participated in chamber tests, patch tests, or field tests involving mustard agents or Lewisite, including at Edgewood Arsenal, the Naval Research Laboratory, Bushnell, Camp Sibert, or other documented test sites.
• You served in a unit tasked with handling, producing, transporting, or destroying chemical warfare agents.
• You served in a theater or era where battlefield exposure has been documented and you have a credible exposure history.
• You have a current diagnosis of a respiratory condition, respiratory cancer, chronic skin condition in a body area that would have been exposed, or another condition the VA has linked to these agents.
• You filed a claim previously that was denied for lack of exposure verification or insufficient nexus, and you are considering a supplemental claim.
• You are a surviving family member pursuing dependency and indemnity compensation tied to a death the family believes was caused by exposure-related disease.

If you fit any of these scenarios, the revised procedures will shape how your claim moves through development and rating.

What to Do Next

Take these concrete steps.

First, pull your service records. You need anything that documents your unit, your duty assignment, your location, and your dates of service during the suspected exposure period. DD-214, performance reports, orders, and unit histories all matter.

Second, request your exposure verification. The Department of Defense maintains records of personnel who participated in known chemical warfare agent test programs. If your name appears on a roster, that verification dramatically strengthens your file.

Third, get your current medical diagnoses documented. A claim for a presumptive condition requires a current, confirmed diagnosis from a qualified medical provider. Make sure your treatment records clearly state the diagnosis using the same terminology the VASRD uses.

Fourth, file or refile through VA.gov, by mail, or with the help of an accredited representative. If a prior claim was denied, a supplemental claim with new and relevant evidence — including evidence of exposure verification you did not have before — is the standard pathway.

Fifth, for any specific legal question about your case, consult an accredited Veterans Service Organization representative, claims agent, or VA-accredited attorney. Do not rely on general guidance for case-specific decisions.

Evidence That Strengthens a Claim Under This Rule

The evidence that aligns with a mustard gas or Lewisite claim falls into three buckets.

Exposure evidence: DoD roster confirmation of participation in a chemical warfare agent test program, unit records placing you at a known test site, buddy statements from fellow participants, and your own detailed lay statement describing the test conditions, duration, and any immediate symptoms.

Medical evidence: current diagnosis from a treating physician using clinical language consistent with VASRD criteria, longitudinal treatment records showing the chronic nature of the condition, pulmonary function tests for respiratory claims, biopsy and pathology reports for cancer or skin claims, and specialist consult notes.

Nexus evidence: for conditions on the presumptive list with verified exposure, no separate medical nexus opinion is required — the presumption supplies that link. For conditions not on the presumptive list but plausibly related, a private medical opinion that explains the biological mechanism and ties it to your documented exposure carries weight.

Organize these documents in the same order the rater will work through them. Clean, indexed evidence is processed faster and with fewer development letters.

Common Mistakes to Avoid

Veterans repeatedly lose ground on these claims for predictable reasons. Avoid them.

Do not assume your exposure is already in the VA's system. Verify it independently and submit the verification with your claim.

Do not file for a vague condition. File for the specific diagnosis a doctor has given you, using clinical terminology.

Do not skip the lay statement. Your own description of the test or exposure event fills gaps the official records will not cover.

Do not give up after a denial without reviewing the decision letter carefully. Many denials hinge on a single missing document — often exposure verification — that can be cured in a supplemental claim.

Do not rely on internet forums for legal strategy. Use them for community, then consult an accredited representative for decisions.

Source & Getting Help

The official source for this update is the VA's M21-1 change log, available at the VA Changes By Date portal. Review the specific entry for Part VIII, Subpart iii, Chapter 3, Section B for the revised text.

For a personalized read on how this update interacts with your file, use Ask Raven to walk through your exposure history and current diagnoses, or run Raven Scan against your existing claim documents to identify gaps before you submit. For any legal question specific to your case, consult an accredited VSO, claims agent, or VA-accredited attorney.