A Fraction on Friction - 37 Degrees

Slip and fall injuries always increase in the fall and the winter months.  Especially during those weather days when there are rapid or significant temperature changes.  On this episode of the MEMIC Safety Experts Podcast, we have another installment of our Fractional Safety Series where we take a quick, but detailed look at a narrow topic.  The focus today is on how temperature affects surface conditions, looking at the 37 degree warning, dew point temperature, and a few tips to help predict less obvious slip and fall hazards.  Check it out at memic.com/podcast   Peter Koch: Hello, listeners, and welcome to the MEMIC Safety Experts podcast, I'm your host, Peter Koch. And today we're going to do another installment of our fractional safety series. Like many topics, safety casts a broad net. So in the fractional safety series, I take a more focused look at a single aspect of a topic, just a fraction of the holes, so to speak. These are typically shorter episodes, but will be packed with information and hopefully some nuggets that you can take back with you. In today's installment of our fractional safety series, we continue with a fraction on friction, slip and fall prevention, and we look specifically at how temperature affects the surface conditions. So let's dive right in. Why does your car, if you have one with an external temperature sensor and we all agree that water freezes at 32 degrees Fahrenheit most of the time, why does your car warn you that at 37 degrees roads may be icy? Well, [00:01:00] is it because that carmakers want a margin of error? Or maybe the programmers felt they needed a harbinger of 32 degrees? Well, if we look at it more closely, we can discover that, though either could be true. Neither are actually the reason. It's all about location and it has to do where the thermometer is located on your car. Most car thermistors or temperature sensors are located somewhere on the front of the car, maybe behind the grill or in one of the side mirrors, and they can be affected by the radiant heat of the walkway. It's a tough engineering decision. You put it too close to the engine compartment and the sensor will be affected by the engine temperature. Burry it too deeply in the vehicle and it won't register the outside ambient temperature at all. It needs to be somewhere far enough away from the engine, but close enough to the outside of the car. Then it can be in the airflow around the car. Accurate readings from these sensors will come after the car has been traveling [00:02:00] at speed and the airflow has normalized for the radiant heat of the roadway. However, in the winter location is also the reason for the warning. At 37 degrees. In the winter, temperatures taken above ground level will be slightly warmer than at the road surface, especially at night after the roadway has cooled. So when the temperature sensor is located in the grill or side mirror, it doesn't reflect the temperature at ground level. Thus, the car manufacturers will give you fair warning that icy conditions are possible at 37 degrees. Well, how does this translate then into slips and falls? Well, similarly, you may have experienced checking the temperature, finding that it's in the mid 30s, and then your first step on the pavement is like stepping on to a skating rink, not even realizing that there's going to be ice there on the ground because, again, water freezes at 32 degrees and the temperature you just checked was maybe 35 or 36 or 38. Think [00:03:00] about where the thermometer that you just checked, whether it's at work or at home, is located. If you have a backyard thermometer or maybe even a window thermometer, those are located well, somewhere that you can see them from a window. And even if you don't have a local thermometer and like many of us, we use a weather app on our phone or computer that might not give you accurate surface temperature reading either, according to weather.gov, when temperatures are officially recorded for hourly weather observations and climate reports, they're measured at a height of between one and a quarter and two meters above the ground. That's between four and six and a half feet. The instruments are housed in special shelters called Stevenson Screens. They are named after the father of writer Robert Louis Stevenson. And meteorologists call this temperature the surface temperature, and that's the temperature that gets reported out to the public. Again, these provide readings of the ambient temperature where the sensor is located, or an average [00:04:00] of many sensors, but not at ground level. During clear and calm nights, the temperature at the ground or some surface near the ground can become much cooler than the reported temperature. The radiation of heat away from the ground is the cause in this drop, in these conditions, the coldest air forms near the ground and being heavier than the air above it remains there. So even when the temperature is in the mid to upper 30s, frost or ice can still form. Just because it's cold, though, doesn't always mean that it's icy. There are other environmental conditions that will factor into the formation of frost or ice on a walkway or road. Let's take a quick break. Peter Koch: Seasons change and with cooler temperatures come slip and fall hazards, sometimes we get complacent and think we've got it covered. But statistics show that slip and fall injuries always increase in the fall and the winter. Did you know that MEMIC has a page on their website about winter safety resources that anyone [00:05:00] can access? It has reminders, tips and checklists that you can use for your home or your business to help you prepare for winter hazards. Check it out at MEMIC.com And search for winter safety. If you are a policyholder with MEMIC, then check out the winter safety resources at MEMIC.com/workplacesafety and log in to safety director. Now let's get back to the Fraction on Friction episode. Peter Koch: So let's talk a little bit about dewpoint. Dew point is the temperature or point at which the air is saturated with water vapor or water in its gaseous state, well all air has some water vapor in it and the amount of water vapor the air can hold varies with temperature. The warmer the air, the greater its ability to hold water vapor. And if the air cools down enough, it won't be able to hold the moisture that it started with and the water vapor will condense into water droplets. Or if the temperatures fall, enough [00:06:00] ice crystals. When the sun is out, the air temperature near the surface is usually above the dew point and water in the atmosphere remains as vapor. However, as the sun sets and the earth radiates heat into space, the air near the surface can cool to the dew point temperature. On cold, clear nights if the surface temperature and dew point temperatures are below freezing, then frost will form. And this can make for some slippery travel. But it tends to form fairly slowly and can be easily managed if we anticipate it. On the other hand, fog can be more challenging, especially when it's colder. Fog often forms on cold or clear nights as the temperatures drop to the dew point in areas where there is abundant moisture, such as around unfrozen rivers, lakes or soil that is still damp or wet. Fog contains large amounts of liquid water. And if a fog bank passes over a walkway, parking lot or roadway that has cooled to a temperature below freezing, icing can [00:07:00] be rapid and take a toll on travelers with a thick coat of ice being deposited in mere minutes. Temperature affects surface conditions in multiple ways, and the media or Internet based sources we normally rely on to influence our decisions for travel may not be enough to keep us safe and upright in some circumstances. Understanding the relationship between air temperature, surface temperature and dew point temperature can help you identify problems and make decisions for future actions. Here are some practical tips for predicting less obvious outdoor slip and fall potentials. So first, clearing skies with low or no wind can indicate rapid radiational cooling potential. This can have an impact on any walkway moisture and raise a red flag for your morning commute or walk to the mailbox when the temperatures start to drop next, the sun helps to melt frosty surfaces. However, surfaces and shaded areas can hold ice well into the day, even when [00:08:00] reported temperatures are above freezing. Next, know your locations, know where you work, live and commute. Are they near water or open fields? Do you normally see fog in those areas on cold or cool mornings when the temperatures start to drop and get into those mid 30s and you expect fog in those areas? Be sure to use caution. And finally, remember, officially reported temperatures are warmer than surface temperatures, especially on cold, clear nights. If air temperatures drop below the thirty seven degree mark, freezing conditions may already exist at the surface. There's a ton more that we can talk about regarding how temperature affects surface conditions. We didn't even get to freezing rain or wind. However, you can check out some additional reading at MEMIC.com/podcast where you can find more resources on this topic and our entire podcast archive. Peter Koch: That about wraps up this weeks, safety expert podcast. Today, we've been exploring how temperatures, even [00:09:00] those above freezing, can indicate freezing conditions and affect surface friction. Thanks again for joining us. If you have any questions on this topic or would like to hear more about a particular topic on our podcast, or you have ideas of other episodes related to safety, email me at [email protected]. And if you haven't already, I'd appreciate it if you took a minute to review us on Stitcher, iTunes or whichever podcast service that you listen to us on. And if you've already done that, well, thank you, because it really helps us spread the word. Please consider sharing this show with a business associate friend or family member who you think will get something out of it. And as always, thank you for your continued support. Until next time. This is Peter Koch reminding you that listening to the MEMIC Safety Experts podcast is good, but using what you learn here is even better.