Batteries commonly used in flashlights and other household devices produce hydrogen gas as a product of zinc electrode corrosion. The amount of gas produced is affected by the batteries’ design and charge rate. Dangerous levels of hydrogen gas can be released if battery types are mixed, batteries are damaged, batteries are of different ages, or batteries are inserted incorrectly. The hydrogen gas can cause the battery compartment to rupture, allowing the hydrogen gas to mix with oxygen. This mixture of gases can cause a powerful explosion in the presence of a spark or excessive heat. However, when used properly, batteries are quite safe for classroom use. To reduce risks associated with batteries, consider the guidelines in this month’s column.