Which of the following is regarded as a casualty agent associated with blood?

Hydrogen cyanide is classified as a casualty agent associated with blood because it functions as a potent chemical asphyxiant. When inhaled or absorbed, it interferes with the body's ability to utilize oxygen by binding with hemoglobin, effectively preventing red blood cells from carrying oxygen to tissues and organs. This makes it particularly lethal and highlights its role as a chemical that affects the blood’s capacity to transport oxygen, leading to hypoxia and ultimately death.

In contrast, choking agents primarily damage the lungs and respiratory tract, nerve agents disrupt the nervous system, and blister agents cause severe skin and mucosal damage, rather than affecting the blood’s oxygen-carrying capacity directly.