NEHA October 2022 Journal of Environmental Health

October 2022 • Journal of Environmental Health 41 takes and successes—and we are still learning. We do not know all the answers but realize it is now our turn to give to the best of our ability our version of an owner’s manual for environmental health practitioners. In so doing, we hope to introduce timely ideas and tips to make your field work easier and seamless. Most important, however, we welcome your questions and comments. We will try to respond in a way that is both useful and in keeping with our collective professional goals. We know there are emerging issues that aect our professional acumen and therefore, we welcome all your comments, opinions, and questions. Most of all, we are open to sharing novel approaches and techniques that you are using that make your job easier, safer, and more concise and understandable. By way of introduction, here are the coauthors of this column: • James J. Balsamo, Jr., MS, MPH, MHA, RS, CP-FS, CSP, CHMM, DEAAS: Forensic sanitarian who specializes in institutional environmental health and safety. • Nancy Pees Coleman, MPH, PhD, RPS, RPES, DAAS: Toxicologist who specializes in occupational and environmental toxicology, environmental data analysis, and risk assessment. • Gary P. Noonan, CAPT (Retired), MPA, RS/ REHS, DEAAS: Environmental health o•- cer and sanitarian who specializes in international environmental health and safety. • Robert W. Powitz, MPH, PhD, RS, CP-FS, DABFET, DLAAS: Forensic sanitarian and local health o•cer who specializes in institutional environmental health and standards development. • Vincent J. Radke, MPH, RS, CP-FS, CPH, DLAAS: Sanitarian who specializes in food safety, policy development, and risk assessment. • Charles D. Treser, MPH, DEAAS: Principle lecturer emeritus of environmental and occupational health sciences who specializes in environmental health regulation, workforce development, and communication. To contact us, send your comments and questions to Checking Field Thermometer Accuracy When conducting a retail food establishment inspection, one of the most critical and often observed violations is the failure to maintain safe temperatures, particularly hot and cold holding. Temperature readings above 41 °F (5 °C) and below 135 °F (57 °C), barring any time component, can result in immediate food destruction or a serious consequence in fines, sanctions, or even closure. On rare occasions, the restaurateur might challenge these findings that include questioning the thermometer accuracy and/or the conditions of sampling. When findings are questioned, it is our responsibility to justify inspection results in a way that cannot be challenged. In occasions when we have worked with a restaurateur to defend their claim, we found that failure to validate and record the thermometer(s) accuracy can and will invalidate inspection findings. We will deal with sampling strategies in another column. For this column, however, we will focus on ensuring accuracy of the temperature measuring devices that we regularly use in the field. The need for validation—to confirm its accuracy or calibration, which is to precisely adjust the instrument in accordance with manufacturer recommendations—is inherent in the temperature measuring device itself. Most electronic thermometers are manufactured to an accuracy of ±0.2 °F (0.1 °C). Mechanical thermometers, such as bimetallic (dial) thermometers, have a tolerance of ±2 °F (1.1 °C). Thermometer accuracy can also be further compromised by external conditions encountered during transport, such as keeping them in a hot car, in freezing temperatures, or subjecting them to jarring before use. Therefore, in the absence of a National Institute of Standards and Technology (NIST)- traceable dry-well thermometer calibrator, validating thermometer accuracy by some simple but traceable means is essential. Conventional wisdom recommends using an ice bath to validate electronic thermometers or calibrate mechanical ones. Presumably, the ice and water mixture will be 32 °F (0 °C) but that is not always the case. A water and ice mixture made from distilled, reverse osmosis, or deionized water will result in a 32 °F (0 °C) bath. A water and ice mixture made from surface, well, or bottled water can dier widely in total dissolved solids (TDS) content and aect the temperature of the mixture. The higher the concentration of dissolved salt, the lower its overall freezing point. The freezing temperature of “pure” versus highly mineralized water can vary as much as ±4.5 °F (2.5 °C). Along with the inherent accuracy of the thermometer, the variance of the ice and water mixture and thermometer together can result in an error as high as ±6.5 °F (3.6 °C). This high possibility for error does not instill a lot of confidence in verification of thermometer accuracy using an ice bath, particularly when a poorly functioning thermometer is used as an enforcement tool. There is a better way. Here is the logic. If the thermometer is used to measure both hot and cold holding temperatures, would it not make more sense to do a two-point validation at some approximate temperature in the hot and cold range? Secondly, would it not make more sense to compare the temperatures of the thermometers to some temperature standard rather than worry about the TDS levels of the water and ice mixture and its freeze point conversion factor? Let us begin by using a “temperature standard” thermometer, which is a liquid-in-glass general purpose laboratory thermometer, preferably built to NIST specifications but not necessarily essential. A convenient temperature range of the temperature standard Calibration and validation array that shows the “temperature standard” thermometer along with the thermometers to be validated (bimetallic dial, thermistor, and thermocouple thermometers), and record book. Note, the black dot on the container shown in the photo is used for validating our infrared thermometer, which will be discussed in a future column. Photo courtesy of Dr. Robert Powitz.