Smoke bombs are intended for outdoor use. Using indoors can set off smoke alarms and sprinkler systems. Smoke is safest when used on concrete surfaces. We do NOT recommend using them in woodsy areas or spots where there is dry, flammable materials such as dry grass, weeds or dead trees. The sparks produced for the first 2-3 seconds upon lighting could land on flammable materials and potentially start a fire. Nothing replaces common sense. If in doubt about using them in certain environments, don't use them.