Chemicals used in war fit into five categories: flame agents, incendiaries, smokes and obscurants, incapacitants and riot control agents, and toxic agents. Flame agents, typically hydrocarbons or other readily flammable liquids, are used in flame throwers and flame projectors such as flame rockets. Incendiaries are often metals such as magnesium or aluminum, or oil and metal mixtures. These materials often require a fuse or ignition cup. Smokes and obscurants may be gaseous, liquid, or particulate aerosols. Incapacitants and riot control agents are designed to incapacitate but not permanently damage. These substances may be atropinemetics, or lacrimators, sternutators, vesicants, or urticants. Effects of atropinemetics may last from a few hours to a few days; effects of the latter materials usually dissipate within minutes upon removal from the agent. The toxic agents are generally of two types, vesicants such as the sulfur or nitrogen mustard gases, or the organophosphate nerve agents. Defense against toxic agents requires agent detection and identification; individual and collective protection of personnel and equipment; decontamination materials and procedures; and medical defense.