I have an infrared thermometer that I’ve played with for a few years. Interesting and fun. I never thought about using it to check for a fever until the covid thing. But, of course, it doesn’t take internal temps. Only skin surface. And I see people using this method for screening people all the time. But what numbers are they looking for when they do it? Clearly, our skin temp varies a lot with the environment. Coming in from a hot sunny day. Sitting in air conditioning. Etc. So when I want to use it to assess health - an admittedly imprecise way - what range of temps should I be looking for? What range to the gatekeepers we see using them to screen entry into events and places use?
Which infrared thermometer do you have? More directly, does it specify a field of view angle? A lot of these thermometers report an average temperature from it’s entire field of view meaning very close to the skin is best.
I heard a story on the radio fairly early in the pandemic about a factory that had converted to building ventilators. Employees had to stand before an IR thermal cam to test for fever prior to entry. One came back some impossible temperature like 120. Turns out they were holding a hot cardboard cup of coffee and that particular thermometer reported only the hottest value in its field of view.
An infrared body thermometer is calibrated to convert the skin temperature to an internal temperature, so the numbers they are looking for are exactly the same as for an internal thermometer. The one we have gives best results when used on the right temple (hold it just away from the skin of the temple, get hair out of the way, etc.)
If I set it for a surface temperature it gives 33.5ºC for my temple as opposed to 36.7ºC when set to “body”.
I guess I don’t know how they can make that conversion. Doesn’t skin temperature vary quite a bit depending on surroundings, activity, etc.? I’m assuming it does, which is why I’m looking for a range of temperatures that would indicate that a person’s internal temperature would be around 98.6F or 37C.
Yes. When I went to the dentist right after their lunch, I had to wait in my car for about 10 minutes until they returned. When they took my temperature it reported 101+, but we both realized it was a false reading. In a couple of minutes inside in the A/C, I registered normal.
If you have a regular oral thermometer, consider taking several measurements, perhaps under various conditions, using it and the infrared thermometer and compare the results and see how they correlate.
Ok, I’ve confirmed that the thermometer is fairly accurate by taking the temp of some water in a glass using an instant read thermometer and then using this infrared one. Maybe .2 degrees off. And when I use the infrared thermometer on my forehead it reads 89.7. When I take an oral temp, I get 99.1. My forehead reads 9.4 degrees less. Should I use that difference as a constant when taking my body temp using the infrared?
You certainly should. Provided you’re in the same circumstances as when you ran your test. E.g. if you’d been sitting still for 5 minutes indoors before you made your experiment then a later reading taken in the same circumstances should have the same conversion factor.
Conventional under-the-tongue thermometers also have expectations about circumstances. Just finished a cup of coffee or a glass of ice water? The under-the-tongue reading will be invalid garbage for 20 minutes. Just finished a 3-mile run in the sun? Ditto.
Thanks, LSLGuy. I was hoping that I’d hear from someone who does that type of temp screening someplace. But your confirmation that I have more or less identified the significant difference should allow me to plug that in when I need to. Still, thinking about it, those screenings must be VERY rough approximations, given the various conditions and circumstances people show up in. Makes me think they’re pretty much for show. But that’s a different thread.
I currently do screening of about 50 to 90 people per day at a college, and we use a non-contact thermometer that’s designed to measure body temperature, and the range of recorded temperatures has been fairly small (e.g., 96.0 to 98.0). Some do get lower temps, such as 92.4, but that’s often due to holding the sensor too far from their forehead, having hair in the way, measuring soon after sitting in an air conditioned car, or bald guys coming in from the rain. After about eight weeks of doing this, there hasn’t been a measurement above 100.4, in which case I’d have to send them away.
The first time I saw a doctor after the shutdown was at my ophthalmologist - and they did the forehead-from-3-feet-away thing. I asked if they’d ever had a high reading and she said that yes, the only time was when a fellow had arrived early and had been sitting in his car. 5 minutes later it was fine.
I have to wonder whether the forehead-thermometer checks are more “security theater” than truly useful.
Yep. This is my conclusion, based on a number of trials. My internal temp varies during the day by about .3 degrees. My skin temp varies from my internal temp by as little as 3 and as much 12 degrees. Theater. Like the security line business.
When measured at your right temple?