Shipping Delays Up to 3 Days - Free Shipping on USA Orders $150 or More

Heat Loss Mechanisms

by Kevin Estela January 29, 2020

Heat Loss Mechanisms

Originally posted on Jan 20, 2016

As I write this right now, New England is getting ready for a wintry mix of snow, sleet and rain. Precipitation will sprinkle drivers with a concoction of winter weather rendering some of their common sense and driving ability useless. Winter is here but knowledge of cold should be considered year round. Even in the desert, nightly cold temperatures can kill. Understanding how the body loses heat helps the outdoorsman preserve it and prolong life. 

Conduction cooling occurs from direct contact with a cold surface. In 30 degree weather, holding your hand out in front of you won’t be of any discomfort but laying down on a 30 degree concrete floor will send chills through the body. A common mistake I’ve witnessed numerous times is failing to insulate from the ground during shelter building classes. Students become preoccupied with protecting from the wind and rain and forget the largest mass below them that will zap the heat from their body. Evergreen boughs, pine needles, bubble wrap, cardboard, anything that creates sufficient dead air space will help protect from conduction cooling.  Try standing on top of a closed foam pad (or a camp chair like the one pictured) and you’ll notice the protection it offers.

Convection cooling results from blowing wind. Anyone who has been a boater, sat in the stands at a football game or who has ridden in the back of a pickup truck knows how cold the wind can feel. Convection cooling is dangerous because even a light wind amplifies the cooling effect of the ambient air temperature. This can go unnoticed, especially if the body is warming itself by activity from the inside out. A common misconception is fleece, minus additional layers such as Gore Windstopper, will protect from the wind. Fleece is a loose fabric and allows wind to come right through the material. A cheap way to protect from the wind is to use a reflective emergency blanket but the key is to keep the blanket off the body. Otherwise, the wind will cool the blanket and conduction cooling (explained above) will take over. 

I still remember coming inside from sledding as a child and my grandmother taking my scarf and wrapping it around neck and mouth. No, she wasn’t trying to snuff me out but she was trying to protect me from getting cold. When we breathe out, we breathe out air that is approximately 98.6 degrees fahrenheit. When we breathe in, we take in the ambient air. If you can see your breath, you are losing heat by breathing. Since you can’t stop breathing, you have to protect your lungs by either staying active or by covering your mouth with a breathable fabric. Note I said breathable, don’t use that space blanket or you’ll end up suffocating. You can fix cold, you can’t fix stupid. 

The human body is an amazing machine. It self-regulates for warmth by releasing moisture in the form of perspiration. This is natural and some folks sweat more than others. Perspiration is one way the body can cool itself dangerously fast in cold weather. The most common form of this comes from working with too many layers on. You see this at trailheads when folks set off with multiple layers on only to shed them when you catch up to them along the way on the trail. If you wear layers that wick sweat away (not cotton in the cold!) bringing it to the outside of your layers, you will find sweat to be less of a concern. It is better to work slightly cooled than too warm. Let your clothing work as intended and mitigate the effects of sweating by wearing only what you need to. 

If you have ever put your hand next to a baseboard heater, you understand radiating heat. Radiation is the amount of heat given off by a mass. The sun, for example, gives off incredible radiating heat as does a person laying next to you in bed who by all accounts “sleeps warm.” Radiating heat can be converted to warmth through good insulation. Wool, Primaloft, goose down, all of these materials can be used to trap radiating heat and keep the body warm. If you are in a pinch, you can stuff cattail fluff, milkweed pod kapok or dried leaves if you have nothing else. As humans, we radiate heat, it’s natural. Take advantage of your natural furnace and maximize the heat you give off by trapping it. This is where emergency blankets come into their own. They do not insulate but reflect heat. If nothing else, if you are cold, a fire can radiate heat toward the body so make sure you are prepared with the means to make one. Add in a fire reflector made of stone and you’ll notice the added heat it provides after the fire dies down.

Of all the heat loss mechanisms, immersion is my least favorite. I’m a kayaker/canoer and a diver and before that a lifeguard for years. After countless dunkings, I wish I could tell you my body has adjusted to cold water exposure but it hasn’t. While I can better manage my cold by layering when possible and rewarming differently (drinking buttered hot cocoa helps!), I've only been able to offset the effects AFTER getting out. When I am in the water, or anyone for that matter, heat escapes the body much more rapidly than any other way in the atmosphere. The exact rate a person loses heat will vary depending on the temperature of the water, what is worn is whether the person is swimming, treading water, or in the H.E.L.P. position. I’ve heard the rate to be 20-40 times that of conduction. In any case, immersion heat loss must be taken seriously. in full-body cases, it leads to extreme exhaustion, unconsciousness and death. In cases where extremities are submerged, extreme cold, numbness and loss of function. The best course of action is removal from the water and if that isn’t possible, positioning your body in a way to conserve heat. 

If you’re able to understand the ways the body loses heat, you can better take action to prevent it. Just as there are ways to lose heat through the body, there are ways to bring heat to the body. Understanding these concepts will help you better survive the wilds of the outdoors in an emergency or from day to day in the winter until those horrible drivers are no longer affected by .




Kevin Estela
Kevin Estela

Author

Kevin Estela is a Survival Instructor at Estela Wilderness Education. Kevin is a frequent contributing writer for publications such as RECOIL, Athlon Outdoors, and Beckett Media. He is a Sayoc Kali Associate Instructor Level 5, as well as a BJJ Purple Belt.



Leave a comment


Also in Articles

The Revolutionary Fixed Blade
The Revolutionary Fixed Blade

by Brian Griffin May 20, 2020

It seems the first fixed blade to be discovered and actually appreciated, presumably via an injury to the discoverer, was quite the revolutionary incident in human history. It's clearly evidenced by how much we have developed all sorts of cutting tools since then. Not only knives in many specialized applications over the last 50 thousand or so years, but cutting tools for all sorts of materials, and with far more of them being developed for utilitarian applications than combative ones. With a good quality multi-tool perhaps being the pinnacle of overall usefulness versus the various materials in an urbanized environment so far. Though obviously with the weaponization of anything it can profitably be applied to being pretty common, as some living in quarantine may currently be suspecting, blades made for war have certainly earned their way into our revolutionary history as well.

Read More

How to Construct a Pine-Bark Bowl
How to Construct a Pine-Bark Bowl

by Kevin Estela May 13, 2020

Can you imagine what it would be like to have the confidence to walk into woods with only a knife and survive? It is a goal, albeit a lofty goal, many people have. It sounds like it requires a lot of skill because it does. There are challenges and difficulties everywhere. You have a knife but what about shelter, food, fire, and water? What about everything else? The sum total of all the issues you must address can be hard to digest at once. However, when you look at each task individually with a knife and a problem-solving mind, the thought of surviving in the woods comes more clearly into focus. For this month’s Fiddleback Forge blog, I’ll focus on one way to address the basic survival need of water. Perhaps one of the easiest ways to make a water vessel is by using pine-bark. As you’ll see, this time of year, you don’t even need to make a fire or use cordage to address your hydration needs.

Read More

The Indomitable Spirit of Humanity
The Indomitable Spirit of Humanity

by Brian Griffin April 29, 2020 2 Comments

It has been 6 weeks since we were made aware that we're facing yet another global pandemic. The occurrence of pandemics is really nothing new to us, as we've experienced several since the Spanish Flu in the second decade of the 20th century, and a few in just the first two decades of our current century. However this one certainly seems to bringing about some new responses, as we are being told to go against all that we've learned about basic human immunology, since that field of study began in earnest in the mid 1800s, and quarantine the healthy in some places as well as the ill. And encouraging an avoidance of our own atmosphere and everyone other than family through the process of social distancing every where else. It's an unusual and counter-intuitive approach, which has had made for some curious visuals in our new paradigm.

Read More

Knives & News

Sign up with your favorite email.