Ham Radio General Class Practice Test

When may a lead acid storage battery emit explosive hydrogen gas?

1. When stored for long periods of time

2. When being discharged

3. When being charged

4. When not placed on a level surface

The correct answer is: When being charged

A lead acid storage battery may emit explosive hydrogen gas primarily when it is being charged. During the charging process, electrolysis occurs, which splits water into hydrogen and oxygen gas. If the charging voltage exceeds the battery’s design limits, it can cause excessive gassing, leading to the buildup of hydrogen gas. This is particularly dangerous because hydrogen is highly flammable and can form explosive mixtures with air. While hydrogen gas can theoretically be released during discharge due to over-voltage situations or internal faults, the typical production of hydrogen gas associated with lead acid batteries is during charging. Proper charging practices, such as using a charger compatible with the battery type and monitoring the charging voltage, are crucial for safety. In terms of the other scenarios, long-term storage does not inherently produce hydrogen gas, as there is no active chemical reaction occurring. Although a battery that is not placed on a level surface may have practicality and safety considerations, it does not directly cause the emission of hydrogen gas. Hence, charging is the correct context in which the risk of hydrogen gas emission is notably heightened.