What tool is commonly used to measure the temperature of smoke during a fire?

A pyrometer is the correct choice for measuring the temperature of smoke during a fire. This instrument is specifically designed to measure high temperatures, making it particularly suitable for the extreme heat conditions typically found in fire situations. Pyrometers can often measure temperatures from a distance and are capable of providing readings without direct contact, which is essential in scenarios where getting close to the heat source would be unsafe.

In contrast, a thermometer is generally used for lower temperature ranges and may not withstand the high temperatures found in a fire. A barometer measures atmospheric pressure and is not related to temperature measurement. A hydrometer is used to measure the specific gravity or density of liquids, which is irrelevant in the context of measuring smoke temperature. Therefore, the pyrometer is the most appropriate and effective tool for assessing the temperature of smoke in firefighting operations.