A blood agent is a toxic chemical agent that affects the body by being absorbed into the blood. Blood agents are fast-acting, potentially lethal poisons that typically manifest at room temperature as volatile colorless gases with a faint odor. Arsine gas, formed when arsenic encounters an acid, is used as a pesticide and in the semiconductor industry; most exposures to it occur accidentally in the workplace.
Cyanide poisoning can be treated with antidotes.
List of blood agents
The information in the following table, which lists blood agents of military significance, is taken from Ledgard. The values given are on a scale from 1 to 10.
{| class="wikitable sortable"
|-
! Agent
! Description
! Melting / boiling point
! Effectiveness as blood agent
! Persistence, open area
! Persistence, enclosed area
! Field stability
! Storage stability
! Toxicity as blood agent
|-
| Hydrogen cyanide
| Colorless gas or liquid, almond odor, burns with a bluish flame.
| −13 / 26 °C
| 10
| 2
| 9
| 10
| 8
| 10
|-
| Cyanogen
| Colorless gas, almond odor, burns with a pinkish flame having a blue border.
| −28 / −21 °C
| 9
| 2
| 9
| 8
| 7
| 9
|-
| Cyanogen chloride
| Colorless gas or liquid, pungent and biting odor, soluble in water and alcohol.
| −6 / 14 °C
| 8
| 3
| 9
| 9
| 9
| 8
|-
| Cyanogen bromide
| Colorless needle-shaped or cubic crystals, tending to volatilize on standing, hence of limited usefulness as a weapon.
| 52 / 62 °C
| 9
| 5
| 8
| 5
| 6
| 8
|-
| Arsine
| Colorless gas, garlic-like odor, slightly soluble in water.
| −117 / −62 °C
| 9
| 3
| 8
| 5
| 9
| 9
|-
| Vinyl arsine
| Colorless liquid, irritating and bitter odor, slightly soluble in water, also acts as a blister agent.
| 124 °C (boiling)
| 7
| 7
| 9
| 8
| 9
| 6
|-
| Phosgene
| Colorless gas and slightly yellow liquid, moldy hay odor, slightly soluble in water and soluble in most solvents, also acts as a choking agent.
| −118 / 8
| 10
| 6
| 9
| 5
| 8
| 6
|}
Sodium cyanide and potassium cyanide, colorless crystalline compounds similar in appearance to sugar, also act as blood agents.
One of the earliest proposed chemical weapons, cacodyl oxide, or Cadet's fuming liquid, also displays properties of a blood agent (as well as those of a malodorant). It was proposed as a chemical weapon in the British Empire during the Crimean War, along with the significantly more potent blood agent, cacodyl cyanide.
Use
The most significant practical application of blood agents was the use of hydrogen cyanide (Zyklon B) in gas chambers by Nazi Germany to commit the mass murder of Jews and others in the course of the Holocaust. This resulted in the largest death toll as a result of the use of chemical agents to date.