The immediate cause of death is usually respiratory failure. Blood agents work at the cellular level by preventing the exchange of oxygen and carbon dioxide between the blood and the body's cells. This causes the cells to suffocate from lack of oxygen. Cyanide-based agents do so by interrupting the electron transport chain in the inner membranes of mitochondria. Arsine damages the red blood cells which deliver oxygen throughout the body. Detection and countermeasures Chemical detection methods, in the form of kits or testing strips, exist for hydrogen cyanide. Ordinary clothing provides some protection, but proper protective clothing and masks are recommended. Mask filters containing only charcoal are ineffective, and effective filters are quickly saturated. Due to their high volatility, cyanide agents generally need no decontamination. In enclosed areas, fire extinguishers spraying sodium carbonate can decontaminate hydrogen cyanide, but the resulting metal salts remain poisonous on contact. Liquid hydrogen cyanide can be flushed with water. 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. Sodium cyanide and potassium cyanide, colorless crystalline compounds similar in appearance to sugar, also act as blood agents. Carbon monoxide could technically be called a blood agent because it binds with oxygen-carrying hemoglobin in the blood (see carbon monoxide poisoning), but its high volatility makes it impractical as a chemical warfare agent. 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. References