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
podcast@MEMIC.com. And if you haven't already, I'd appreciate it
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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.