Entry into a confined space for any type of hot work must be prohibited when tests indicate the concentration of flammable gas in the atmosphere is greater than _____% of the lower flammable limit.

The correct answer is based on established safety protocols for working in confined spaces where flammable gases are present. When the concentration of flammable gas exceeds 25% of the lower flammable limit (LFL), the risk of ignition becomes significantly elevated. At this concentration, even a small spark can potentially ignite the gas, leading to an explosion or fire.

The lower flammable limit is the minimum concentration of gas in the air that will ignite if an ignition source is introduced. Therefore, exceeding 25% of this limit indicates a hazardous environment where hot work—such as welding, cutting, or grinding—should be strictly prohibited to ensure the safety of workers.

This threshold reflects a safety margin designed to prevent accidents in confined spaces, where ventilation is often limited, and the accumulation of flammable gases can occur rapidly. Monitoring the concentration levels is critical in order to maintain a safe work environment and comply with safety regulations.