Which piece of firefighting equipment helps to determine if a firefighter is in a dangerous environment?

The atmospheric meter is crucial for assessing whether a firefighter is operating in a hazardous environment. This device measures various atmospheric conditions, including levels of oxygen, flammable gases, and toxic substances. By analyzing these factors, the atmospheric meter helps ensure that firefighters are aware of potentially life-threatening conditions such as low oxygen levels or the presence of harmful gases before they enter a scene. This information is vital for making informed decisions about entry and developing strategies to protect the safety of firefighters and other personnel involved in firefighting operations.

The other options, while important in their own right, do not directly assess the safety of the environment firefighters are entering. For example, smoke detectors are designed to detect the presence of smoke, which indicates a fire, rather than measuring atmospheric conditions. A portable water pump is used for water supply and application in firefighting, while fire extinguishers are tools for putting out fires but do not provide information about the surrounding atmosphere.