Which piece of equipment is specified for sensing flammable gas concentrations?

The photoionization detector (PID) is specially designed to sense and measure the concentration of flammable gases in the environment. This device works by utilizing ultraviolet light to ionize gas molecules, allowing for the detection of various volatile organic compounds and other flammable materials. By measuring the resulting current from ionized particles, the PID provides a quantitative analysis of gas concentrations, making it an essential tool in hazardous materials response and monitoring situations where flammable gases may be present.

Other options like thermometers, radiation survey meters, and environmental probes serve different functions. A thermometer measures temperature and does not provide information about flammable gas concentration. Similarly, a radiation survey meter is used to detect and measure ionizing radiation but is not suited for flammable gases. An environmental probe typically monitors various environmental factors such as pH, temperature, or humidity but does not specialize in detecting flammable gases. Therefore, the photoionization detector is the most appropriate and specified equipment for sensing flammable gas concentrations.