Road flares are only good for a few years, and they should be disposed of properly once they have reached the end of their life cycle. Flares contain perchlorate salts, which are used to enhance combustion. With perchlorate mobile in water, contamination from the substance can persist in groundwater for long periods of time, potentially causing negative environmental impacts and possibly thyroid problems in humans. Because of their potential to leech contaminants into the environment, and because of the safety hazards presented by simply throwing a road flare in your trash can, it is important to utilize proper disposal methods when your road flares are out of date or you no longer need them.
Place road flares in a plastic zipper bag and then zip the bag firmly closed. Place the zipped plastic bag inside of a trash bag, and store it somewhere safe. Bagged flares should not be placed where children or animals can get to them, nor should they be left in the yard where perchlorates might have the opportunity to leech into the soil.
Call your trash company to find out if they have a hazardous-materials pickup day or will accept hazardous materials at the local facility. If not, they can direct you to a local facility for hazardous waste management. Alternatively, contact your area fire department or police station.
Take flares to the appropriate facility during their regular business hours. Because flares may pose a safety hazard in addition to an environmental hazard, it is important to drop them off as soon as possible. Make sure that you inform the recipients that you are dropping off flares, tell them whether or not the flares have been used, and tell them the procedure that you used for bagging up the flares.