Heat, sparks, open flame, open containers, and poor ventilation. Incomplete combustion can generate carbon monoxide and other toxic vapors.
Peroxides can form after long-time storage with exposure to air.
Light and heat can accelerate peroxide formation. Peroxides may form which may be unstable under certain conditions. Water will not be effective in extinguishing a fire and may spread it, but a water spray can be used to cool fire-exposed containers. Wear full protective clothing and self-contained breathing apparatus. Heat will build pressure and may rupture closed storage containers.