Which method is not acceptable for checking the temperature of a hot spot on a refractory lined vessel?

Using your hand to check the temperature of a hot spot on a refractory lined vessel is not an acceptable method because it poses significant safety risks and lacks precision. Human skin cannot withstand high temperatures safely, and this method would expose the individual to potential burns or injury. Additionally, it does not provide accurate or reliable data regarding the actual temperature of the surface, as individual sensitivity to heat can vary greatly. In contrast, utilizing thermocouples, infrared temperature measurements, and contact thermometers are all established and safe techniques that provide accurate readings of surface temperatures without risk to the operator's safety. These methods are designed to measure temperature effectively and are essential for ensuring safe operational conditions in pressure vessels.