There are several circumstances under which an officer may generally fire, with intent to wound rather than kill: at an inmate carrying or attempting to obtain a weapon, at an inmate who has attacked another person and refuses to halt when ordered, at an escaping inmate who cannot be stopped by other means, to protect equipment or vital property, or as a last resort in mass escapes or serious assaults. Firearms should be used within the facility perimeter only as a last resort, and public safety must be a priority when they are used outside the perimeter against an escapee. Sharpshooters must be properly trained and qualified in the use of specific weapons, and knowledgeable on the "rules of engagement" under which they may fire either upon specific orders or under pre-authorization. All staff authorized to use firearms must be trained in their use, safety, care, and limits. In riot situations, prison authorities may have to authorize the use of tear gas or smoke compounds to prevent serious injury or loss of life, to suppress escalating disturbances, or to prevent extensive or willful destruction of property. Gas grenades and guns dispense the gas in a relatively controlled manner; other methods include aerosol dispensers and fixed placement gas systems. Officers using riot control gases need to be trained in gas characteristics, agency policies, tactical deployment, individual protection, and first aid measures. Restraint equipment, including handcuffs, belly chains, black boxes, ankle shackles, strait jackets, and restraining sheets and straps, are used as precautionary measures to prevent assaults and escapes, serve medical purposes, prevent inmate self-injury, and prevent property damage.