Which of the following statements is true concerning canister-type gas masks?

Correct Answer: Option D — All of the above.

Canister-type gas masks are air-purifying respirators, not self-contained breathing apparatuses. They are specific to certain contaminants, have limited service life based on chemical saturation, and provide no oxygen. Therefore, all listed limitations are critical safety factors for personnel operating in hazardous or oxygen-deficient environments.