Which device is used to ensure the atmosphere in the tank is safe for entry?

The device that is utilized to guarantee the atmosphere in a tank is safe for entry is the explosimeter. An explosimeter is designed to measure the concentration of flammable gases and vapors present in the air. It provides a quantitative assessment of whether the environment poses a risk of explosion by detecting the levels of combustible components against safe thresholds. This is crucial in confined spaces like tanks, where the accumulation of flammable gases can create hazardous conditions for personnel entering the area.

In contrast, the other devices mentioned serve different purposes and do not specifically assess explosive atmospheres. A thermometer measures temperature, which does not provide information about gas concentrations. A barometer measures atmospheric pressure, and while it can offer insights into weather changes, it does not indicate the presence of dangerous gases. A moisture meter is concerned with detecting humidity levels and is not relevant for evaluating the safety of a tank atmosphere in terms of flammability. Thus, only the explosimeter is the appropriate choice for ensuring safety before entry into a confined space.