Mustard gas just irritates your trachea and your eyes. The chemical suit is unnecesary.
uh, you might be confused, when mustard gas comes into contact with any part of the human body it causes burns like these (image below), which is known for being incredibly painful but not quickly lethal.

Sulfur mustard is a type of chemical warfare agent. These kinds of agents cause blistering of the skin and mucous membranes on contact. They are called vesicants or blistering agents. Sulfur mustard is also known as “mustard gas or mustard agent,” or by the military designations H, HD, and HT.
Mustard gas, or sulfur mustard (Cl-CH2CH2)2S, is a chemical agent that causes severe burning of the skin, eyes and respiratory tract. It can be absorbed into the body through inhalation, ingestion or by coming into contact with the skin or eyes.
- Center of Disease Control