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keeping warm when camping or hiking

Introduction

  • hypothermia is a major risk for hikers and campers in cold conditions especially if they are under-prepared, get wet or they have to stop moving due to having to rest, sleep or from injury
  • every 10kph increase in wind speed results in approximately 2degC colder apparent temperature1)
  • cognition becomes impaired when body temperature falls below 35degC and this is likely to create a vicious cycle of further hypothermia as the person no longer makes good judgements to protect themselves
  • shivering is an important survival mechanism when the body gets cold and is maximal when core temperature reaches 35degC but shivering ceases when the body temperature falls below 31degC in which case death is likely to ensue as temperature continues to fall without the protective capacity of shivering.

Suggested clothing gear for winter hiking

  • thin merino beanie
  • polar fleece beanie can be worn over the merino beanie for extra warmth
  • gloves:
    • consider a thin wool liner glove
    • flexible warm main glove large enough to allow wearing the optional thin liner glove when you need extra warmth eg. Rab Velocity gloves
  • spare 20,000mm waterproof hard jacket with hood
  • puffer jacket - with hood and long sleeves if heading to sub-zero hikes
  • mid layer thin merino wool long sleeve zip skivvy jacket with hood - allows unzipping to reduce warmth so you don't perspire too much
  • non-cotton tee shirt (cotton is fine if not going far from your car and you can change if it gets wet)
  • soft shell trousers eg. Ternua Kosufit Softshell
    • warmer weather you can get away with shorts and thin waterproof rain trousers to wear as needed
    • at night you would probably need to add thermal legging pants
  • sunglasses if going to snow
  • socks
  • flexible light waterproof boots or hiking runners
  • thermos with hot water
  • hand warmer eg. USB type that can also power your phone https://unigearshop.com/?ref=FlgDCdUupTM7wI or chemical type
  • if going in ice/snow conditions:

Sleeping bags

  • for temperatures above 8-10degC I prefer to use quilts (or an open sleeping bag)
  • for temperatures below this a sleeping bag is probably the best weight for warmth option as it more effectively reduces draughts than a quilt (unless you have OCD with binding your quilt to the mattress)
  • as with nearly everything in camping there are major trade offs you need to make in choosing a sleeping bag: cost vs weight vs warmth
    • as a general rule most campers in southern Australia, especially if they camp inland in autumn, winter or spring will need a sleeping bag with a women's COMFORT rating of around 0degC or lower (it can be opened out for warmer nights and for cooler nights supplemented with thermal sleeping bag liner, thermal underwear, etc)
      • for such a bag, you could buy one for:
        • around $100 BUT it will probably weigh over 2kg and be bulky - so NOT a great option for hiking but fine for those camping near their car
        • around $300 can get you a down bag weighing 1.5kg and a comfort rating of -10degC but is still quite bulky at 40x19cm eg. Denali Capsule 700
        • around $400 - this will get you to around 1kg weight and be adequately compact for most hikers eg. S2S Trek
        • around $600-800 - this might get you to around 500-700g and be very compact
    • for those going into alpine regions especially where snow is possible, a much lower rated sleeping bag would be advisable - perhaps a comfort rating of minor 10degC or so.
    • for those who only camp near the beach or in summer, a comfort rating of 10degC may suffice - or just use a quilt
  • in addition, if temperatures are less than 10-15degC you really need thermally insulated sleeping mat with an R rating of at least 2.5 - the higher the better, but also the heavier or more expensive it will be

Additional survival in the snow

  • shovel to build a snow wall or snow cave to protect against the wind
  • axe and saw are handy to chop fallen branches to provide additional support to snow wall and also for supports for your tarp and firewood
  • tarp, guy ropes and pegs (unless you have a 4 season hiking tent)
  • a properly rated thermal mat to sleep on plus a thin foam mat
  • winter sleeping bag
    • consider having 2 bags which can be used inside each other and then supplement with a silk inner - this allows good temperature control
    • or a sleeping bag with comfort rating BELOW the minimum temperature you will experience and then supplement that with:
      • merino wool sleeping bag inner
      • warm dry thermal underwear (not the gear you hiked in all day - place that on top to dry out)
      • thin woolen beanie
      • thin woolen top with hoodie to keep neck warm
      • hot water in drink bottle placed inside your spare merino wool socks (make sure it does not leak)
      • ensure only your face is sticking out of sleeping bag have everything else drawn around your face to keep the warmth in and ensure your breathe is not going into the sleeping bag which will make it wet and cold
    • remember not to get into the sleeping bag while you are cold, exercise first without getting sweaty
    • consider putting your clothing you will wear in the morning INSIDE your seeping bag so they are warm in teh morning plus the take up dead space inside the sleeping bag and keep you warmer
  • survival blanket
  • waterproofed down padded pants are a nice addition for when not moving
  • personal radio beacon to call for help
  • preferably gear to have a wood fire (as a minimum, a propane gas hiking stove to boil water - but it will use a lot of gas to melt snow!)
    • portable titanium wood stove is awesome but most don't carry those when hiking!
    • minimum is a fire rod to start a fire and fire starter
    • dry kindling
  • high calorie food - creates heat during digestion and gives you energy
    • you can cook whole potatoes in a fire if wrapped in aluminium foil

Hypothermia due to immersion in cold water

Exposure time for core temperature to fall to 35.5°C

Water temp ankle deep knee deep waist deep neck deep
10-12degC 7hrs 5hrs 1.5hrs 5 minutes
13-15degC 8hrs 7hrs 2hrs 5 minutes
15.5-18degC 9hrs 8hrs 3.5hrs 10 minutes
18-20.5degC 12hrs 12hrs 6hrs 10 minutes
>21deg C no limit no limit no limit 30 minutes

NB. times are half that (except for neck deep) if it is raining; those with less body fat or higher surface area may have less times;

Adult naked dry body and ambient air temperatures at rest without wind chill or sunlight

  • naked is used here to make it easier to compare needs, obviously if one were to wear clothing, this would alter these temperature recommendations significantly depending upon the insulating effect of the clothing
  • sleeping naked in tent at night on an insulated sleeping mat without wind chill
    • temperature > 24degC - feels increasingly too warm as temp rises and for comfort need increasing wind chill as temperature rises
    • temp 21-24degC - the most comfortable sleeping temperature naked without covering but some may prefer a sheet at 21degC (or if there is a draught)
    • temp 18-21degC - start to feel a bit chilly so a sheet covering will generally be adequate
    • temp 13-18degC - chilly, so a summer hiking quilt covering +/- head and neck covering will give adequate comfort
    • temp 11-13degC - chilly, so a summer hiking quilt covering + long sleeve top + socks +/- head and neck covering will usually give adequate comfort
    • temp 5-11degC - need a higher rated quilt covering for warmth plus socks, head and neck covering + long sleeve top
  • the lower critical temperature (LCT) is defined as “the ambient temperature below which the rate of metabolic heat production of a resting thermoregulating tachymetabolic animal must be increased by shivering and/or non-shivering thermogenesis in order to maintain thermal balance”. LCT for humans is probably around 25-26degC (23degC if lying on a stretcher bed)
  • for a resting naked adult, ambient temperatures below the LCT and above the hypothermia zone are considered to be in the metabolic zone where basal metabolic rate of ~75W increases to its maximum of around 150W to match the extent of dry heat loss before plateauing in the hypothermic zone 2)
  • most will start to feel increasingly cool as temperatures drop below 25degC
    • obviously sunlight will keep you warmer depending upon its strength, and you may tolerate temperatures down to 12degC naked
    • wind chill will significantly impact comfort levels and hypothermia risk
  • shivering is initiated when cold temperature sensors on the skin (especially hands or feet) drop below 33degC and these fire maximally when they fall to 20degC
  • if suddenly exposed to 10degC:
    • 1st shivers appear in 6-7 minutes and they become generalised by 10-11 minutes and can increase heat production of the body 5-fold
  • manual dexterity begins to be reduced as ambient temperatures of hands falls below 12degC, while touch sensitivity falls at ambient temperatures below 8degC
  • if skin temperatures fall below 10degC, the skin blood vessels start cycles of dilation to provide oxygen and nutrients to skin and constriction to conserve heat but at risk of development of frostbite tissue damage
  • a light summer camping quilt will be adequate comfort cover for temperatures down to 13degC but a more insulating quilt is needed for comfort below 12-13degC assuming there is a thermally insulated mattress to lie upon
  • one can sleep comfortably in air temperatures of 12-13degC without shivering and without any covering to the trunk if one lies upon a heat source such as a 50W electric blanket and the head, hands and feet are kept covered.
  • cold adaptation can modify the tolerance to cold ambient temperatures
    • this may be related to a high basal metabolic rate and a higher amount of brown fat stored which is more readily converted to heat before the need for shivering
    • the threshold set point for shivering is shifted to the left for cold adapted and the elderly (making the elderly more prone to hypothermia)
    • evolutionary changes also have an impact:
      • Inuits have a basal metabolic rate 50% higher than persons living in a temperate climate do, and have relatively more sweat glands in the face and less on the body
      • Australian aborigines are able to sleep naked on the ground even at low temperatures

Insulating effects of clothing

  • CLO is a value that describes the degree of insulation provided by an article of clothing
  • A CLO value of 1 is equal to the amount of clothing required by a resting human to maintain thermal comfort at a room temperature of 21degC and is based on a typical business suit, which includes a shirt, undershirt, trousers, and suit jacket.
Clothing CLO value
None 0
Briefs 0.04
Pants with long legs 0.1
Sleeveless shirt 0.06
T-shirt 0.08
Long sleeved blouse 0.15
Flannel shirt 0.3
Shorts 0.06
Trousers 0.15 thin - 0.24 thick fabric
Work coveralls 0.5
Sweater 0.20 thin - 0.35 thick
Down jacket 0.55
Parka 0.70
Socks 0.02
Boots 0.05
Light skirt 15cm above knee 0.01
Heavy knee-length skirt 0.25

source: https://roastsurvey.com/blog-post/understanding-clo-values/

Keeping warm

  • down should only be used for relaxing at camp or sleeping
    • down jackets rip too easily or at risk of getting wet when hiking and are susceptible to ember burns around the camp fire
    • down booties are great in winter and you can get waterproof covers for them for walking around camp
  • wool is generally the best fabric next to your skin - consider netted wool for lighter and more breathable fabric
    • eg. Brynje or Aclima
    • for only a day or two hikes, synthetics may be OK but they will still start becoming malodorous more quickly than wool
  • consider woollen or alpaca fleece hoodies instead of synthetic fleece (this is useless when wet)
    • these are much better around the campfire than down jackets as less damage from embers and wool is self-extinguishing
  • have a selection of layers to choose depending upon temperature and level of activity
    • consider a thin woollen toed inner sock and a woollen outer sock for hiking as you should be less prone to blisters
    • consider a thin woollen / Australian possum down inner glove and a range of outer glove/mitts
  • a wet, cold swag in winter will make you very cold - if rain or dew is forecast, cover it with a tarp or 4WD awning and consider elevating on a stretcher bed
  • be prepared
    • even on short day hikes, no one expects to get lost, injured or caught in an unexpected storm
    • be sensible and take precautions pending the risks of your activity
    • take wet weather gear and some form of shelter even if it is just an ultralight tarp and bivvy bag
    • take a map and compass and a radio beacon (EPIRB)
  • protect against frostbite
    • frostnip is an early stage of frostbite before the skin cells freeze and often first effects tip of nose, tip of ears and fingertips and can be corrected by covering but may result in sunburn-like effect with skin later peeling off
    • frostbite (skin death) usually occurs when skin temperature falls below below −2°C, lesser degrees may cause chilblains
    • frostbite to the exposed face in an otherwise properly dressed person is likely to occur when Wind Chill apparent temperatures fall below minus 25degC which would equate to 50kph winds with ambient temps at minus 14degC
    • frostbite to fingers and toes will occur at much less extreme cold conditions
    • when apparent temperatures drop below 4degC, cover your skin especially your feet and hands and keep them dry
    • take a spare pair of gloves, etc in case they get wet
    • consider chemical pocket warmers
    • if frostbite occurs:
      • do not re-warm the skin if there is risk it will freeze again as repeat warming-freezing cycles cause more tissue loss than delayed re-warming
      • if further freezing is not expected, rapidly rewarm by immersing in 39-42degC water
      • start one aspirin per day
      • do not drink alcohol or smoke
      • elevate the affected part
      • manage as per burns
  • don't get wet
    • many fabrics such as cotton and down loose much of their insulating properties when they get wet - generally avoid hiking with cotton or denim, and don't get your down gear wet! Consider synthetics if getting them wet is likely as synthetics generally retain their insulating properties better and they tend to dry out faster. A wet canvas swag will act as a cooling fridge and will take a long time to dry out!
    • don't wear your full arm length puffer jackets while hiking unless it is extremely cold - you will just perspire too much - wear layered breathable clothing even if its raining
    • dry off as soon as possible
    • avoid perspiration before going to sleep - avoid exertion, excessive clothes (add layers as temperatures drop)
    • keep wet gear outside the tent
    • don't sleep with your head inside the sleeping bag - this will make your sleeping bag wet from your exhaled breaths
    • minimise and manage condensation in tents
    • if you pitch your tent on frozen ground, make sure it is not a river channel - the ice may melt to expose a stream or it may rain and flood your tent!
  • keep thermal wear clean as well as dry
    • dirt impairs insulating properties
  • don't get injured in cold weather
    • this will impair you ability to keep warm by moving and to seek shelter
  • have a shelter from the rain and wind
    • whilst tents are poor thermal insulators, in addition to protection from rain and wind chill, they can create a microclimate by helping to retain some body heat - especially if the tent is small and the canopy is full fabric rather than mesh
    • a 2-man tent fly with minimal wind will provide 0.4 to 1.4deg warmer microclimate than outside
    • a mesh canopy combined with a tent fly will probably be marginally warmer than a fly alone as the mesh does reduce wind flow
    • a 2-man fabric canopy tent with fly and mesh doors with minimal wind will provide approx 4 deg warmer by the end of the night microclimate than outside
    • a 2-man fully enclosed fabric canopy tent (apart from opposite ceiling vents) with fly and fabric doors with minimal wind will provide approx 5-6deg warmer by the end of the night microclimate than outside and probably warmer than this if occupied by 2 people. It will probably give at least 3-4deg extra warmth (and much more effective warmth if there is wind chill in the mesh tent) towards the end of the night compared to an all mesh tent with fly - thus you need to compare the weight savings of a mesh tent with the extra weight (perhaps 250g) of a thermal liner for extra sleeping bag warmth, although a liner does not help with the inspired air temperature
  • reduce your heat losses:
    • don't get sunburnt during the day - this will increase heat loss from inflamed red skin
    • don't drink too much alcohol - this will increase heat loss from skin as it opens up the skin blood vessels when they should be closing down
    • cover your skin including head, feet and hands
      • generally layered clothing is best so that you can regulate your warmth without getting too hot and sweaty
      • thin merino long arm tops and long johns are popular undergarment layers for cold weather conditions
    • use an insulating sleeping pad - much of your heat loss during sleep is via conductive losses to the cold ground, this also applied when sleeping in a hammock
    • use an appropriate sleeping bag or quilt with appropriate thermal clothing layers as needed without causing perspiration
    • sleep in the least amount of clothes that will stop you feeling cold
      • have additional layers inside your sleeping bag to keep them warm should you need to layer up during the night as the temperature drops
    • don't sleep in your socks or underlayer (eg. thermal top/longjohns) you have just hiked in - have a clean warm pair of socks and underlayer reserved for sleeping
    • consider zipping up your jacket and slipping it over the bottom end of your sleeping bag to give your feet an extra layer of warmth
    • consider putting your DRY, CLEAN clothes in your sleeping bag so they are not so cold when you put them on the next morning and put anything unclean such as boots in a plastic bag inside the tent so they are not freezing in the morning
    • reduce your surface area by curling up into a fetal position and have hands between thighs
    • in very cold climates, have a pee bottle - saves you getting out of the tent at night and the bottle will keep you a little warmer, alternatively, ensure you have some sandals to slip on to go out rather than needing to put your boots on
  • add extra heat
    • warm food and drinks
    • radiant heat from a fire outside your tent
    • hot water bottle such as Nalgene bottle placed in a sock (or perhaps warm stones from the fire)
    • go for a walk or do gentle exercise prior to sleep to generate some muscle heat but without creating perspiration
    • sleep with a partner
    • consider additional heat sources such as:
      • hot water bottle
        • ensure it doesn't leak; place near trunk rather than at feet;
      • USB-powered heating pads
        • these are very small and low power output but make great heating pads for small pets
        • 12V car seat heater cushions
          • generally rated at 45W are around 20-24W (2A) averaged as cycle in ~5 min periods of On/OFF and will raise 2P fabric enclosed tent temperature by around 2-4degC as well as providing direct heat
        • 12V throw rugs (usually around 45-60W max)
          • this are NOT designed to lie on hence are not true electric blankets!
        • 12V electric blankets to lie on
        • 12V electric blankets can make life much more pleasurable in winter if car camping and help to warm the air up which your sleeping bag won't do
        • must ensure they do not scrunch up and create hot spots - use bungee cords and tarp clamps to hold them in position
      • 12V 130W 10.5A air heater (designed for demisting car windows)
        • will raise temp from 13 to 19degC within 10 minutes in a full fabric 2 man tent but will drain battery fast if left on!
      • wood stoves
        • these are fantastic for cooking on, roasting in the oven, boiling water (including for warm showers), drying out clothes and towels and can be used to warm up your tent while you are awake
        • they are NOT for keeping tent warm overnight while you sleep - safety issues plus you need to add more wood every 30-60min
        • efficient use of wood - uses ~1kg hardwood kindling per hr
        • chimney stove jack must be fire retardant and you should use a triple shield chimney section to reduce temperatures on the stove jack
        • minimal carbon monoxide risk given they are well flued as long as the chimney damper is kept open- well ventilated areas only
        • significant combustion risk to flammable materials
        • needs a tent with stove jack or chimney placed outside the tent
        • most are too heavy for hiking but 1-2kg titanium models are available for relatively short hiking
        • these are game changers for car camping in winter and can make a big difference if you do get wet or need to ride out a long rain period in cold weather
      • gas heaters
        • these use a LOT of gas - one cartridge may only last 3hrs
        • major carbon monoxide risk - well ventilated areas only
        • significant combustion risk to flammable materials
        • NOT my recommendation for tents
      • diesel heaters
        • heavy, bulky, need to be outside a tent with duct into tent and can be noisy
      • NB. each 10Ah of 12V LiFePO4 battery capacity will weigh at least 1.1kg (see battery systems for camping)
  • carbon monoxide poisoning is a major risk in poorly ventilated enclosed spaces such as tents if fuel is burnt inside or nearby
    • carbon monoxide (CO) is a colorless and almost odorless gas that results from the incomplete combustion of hydrocarbon fuels when oxygen levels are to low (for LPG, the ratio of air to propane needs to be greater than 24:1 to avoid CO production)3)
    • levels of CO above 100ppm create risk as poisoning is cumulative with duration of exposure
    • levels above 800ppm may result in unconsciousness within 2 hours and you may not wake up to extract yourself and ongoing exposure may result in death
    • levels above 1600ppm (1.6%) may result in death within 2 hours
    • levels above 1-2% may result in death after only a few breathes
    • the effects are greater at high altitudes above 3,000m where oxygen levels are low
    • smoke from a wood fire usually has around 5000ppm CO - does not require much to get into a small tent to be lethal!
    • for gas stoves with incomplete combustion, the rate of CO production depends upon two factors: the amount of fuel burnt by the stove and the degree of incomplete combustion.
    • running a small camp gas stove in an A-frame tent with small vents for 15 minutes resulted in CO levels of stabilising around 100-130ppm as production equals ventilation losses of CO, especially if the flames hit the bottom of the cooking pot - elevation of the pot by 25mm significantly reduced incomplete combustion; 2hrs of use at these levels would cause 5% reduction in oxygen saturation of Hb which could be critical at high altitudes 4)
  • if you do decide to use a gas heater in a well ventilated tarp or tent space make sure you have a CO detector alarm!

making the air warmer in your tent to minimise asthma attacks

  • we have evolved to minimise cold air hitting our lungs - prolonged breathing of cold air is not going to make you healthier and for some will make breathing problematic!
  • having a lovely warm sleeping bag does not help much if the air temperature drops below 10-12degC and you suffer from cold-induced asthma attacks
  • first you need a tent that can have ventilation reduced to almost nil - see comparison of full fabric 2P and 3P tents for colder nights
  • your body is a 100W radiator and can be used to heat the air rather than your sleeping bag, but to make this comfortable, you will need a 12V “48W” thermal mat (these cycle on and off every few minutes so average power use is around 24W) or 12V electric blanket under you and you will need nice warm socks and a quilt to help keep you warm depending upon ambient temperatures
  • for rapid warming of the air, a brief usage of a 12V 130W car air demister heater +/- 65W laptop will help
  • a heating mat or electric blanket under you allows you to sleep naked so your body heat instead of being trapped in a sleeping bag will add around 5-7 degrees extra warmth to the air temperature inside the tent if it is a full fabric tent and can retain the warm air (a further 2 deg warmth if also are running a laptop)
  • the increased air temperature will also reduce or prevent condensation in tents
  • see also insulated tents
    • these can raise the air temperature by around 9degC with one person inside as long as they are not inside a sleeping bag
    • they can raise it significantly more even with the heat from a candle!

Mechanisms of heat loss from the body

respiration

  • the body is constantly losing heat by warming up and humidifying the inspired air
  • this can be reduced by warming the air before we inspire it (eg. sleep in an enclosed tent rather than under a tarp)

evaporation

  • when moisture evaporates it uses heat to do so and thus cools the skin in the process
  • this is the main mechanism we manage high temperatures but it also becomes a very important factor in creating hypothermia if we are cold and wet (eg. from perspiration whilst exercising or becoming too warm)
  • it is also the reason why reducing condensation in tents is important so you don't get wet while sleeping

convection

  • if the air layer close to your body is constantly changing, your body loses heat as it is constantly heating up the air layer
  • this is why wind chill is such an important factor
  • wind protection such as layered wind-resistant clothing, a tent and sleeping bag all contribute to reducing convective losses
  • convection loss is dependent upon:
    • area of skin exposed and the degree of insulation over that skin
      • your head accounts for 10% of the body's surface area but becomes a much higher proportional source of heat loss when the rest of your body is insulated by clothing but your head is not - hence in the cold, wearing a beanie or similar is important in reducing your heat losses
    • wind chill: air temperature and air speed but further compounded if skin is wet

radiation

  • all things radiate heat at a rate to the 4th power of the temperature in degrees Kelvin
    • rate of heat loss = constant x surface area x temp in Kelvin4
  • you can retain some of this by use of reflective materials around your body such as “space blankets” and insulating clothing to retain this heat near the skin
  • if you are trying to warm yourself near a fire, wearing layers of insulation will dramatically reduce the radiant warming effect of the fire so one needs to weigh up the pros and cons of clothing with regard to its protection from wind chill etc vs impairing heat gain from the fire

conduction

  • heat flows from a high temperature source (your body) to a lower temperature area (eg. the ground you are lying on and the air layer close to the skin, or worse, very conductive materials such as cold metal close to the skin)
  • the rate of this heat loss is dependent upon:
    • the temperature gradient (this would be equivalent to voltage differential in electric currents)
    • insulation factors (this would be equivalent to resistance in electric currents)
  • this is why an insulating sleeping pad is important when camping

urination

  • this is a less important source of heat loss however if you drink a lot then you will urinate a lot and the urine will be at body temperature so you are losing heat from the body
  • avoid drinking lots of alcohol!
  • but drink enough water to stay hydrated

Mechanisms of thermoregulation of the body

  • the first body response to cold is to divert blood from skin to maintain core temperature and this makes skin cold and pale and the increased effective blood volume causes cold diuresis and your bladder will fill up
  • shivering is a body response to generate heat and is dependent mainly on the temperature of hands and feet as these are usually the first parts to cool down as the body reduces blood flow to these high surface area regions to retain heat
  • shivering will increase respiratory minute volume, oxygen consumption and respiratory quotient and requires energy

perspiration if too hot

  • humans have evolved an important mechanism of perspiration to increase evaporative heat loss in hot conditions
  • this is less effective when it is hot and humid

hyperventilation if too hot

  • this is why hairy animals which cannot use perspiration as significant form of heat loss (eg. dogs) need to pant in hot weather

peripheral vasospasm of skin if too cold

  • the sympathetic system is activated resulting in peripheral vasoconstriction, piloerection, increased muscle tone, release of thyroid hormones and catecholamines, and activation of thermogenesis in brown fat and of course the renown penile “shrinkage” in the cold (erection is a parasympathetic response not a sympathetic one!)
  • reducing blood flow to the skin reduces heat loss from the skin but also risks frostbite
  • excessive alcohol can impair this as alcohol is a vasodilator and thus increases risk of hypothermia

thermogenesis by burning brown fat

  • brown fat is rich in mitochondria and readily generates heat when activated
  • capacity of brown adipose tissue (BAT) to dissipate energy is mediated via the catecholamine-induced B3 adrenergic receptor upregulation of the expression of brown-fat-specific mitochondrial uncoupling protein 1 (UCP1) which is inhibited by glucocorticoids (accentuated inhibition by falling sex hormone levels)
  • BAT is also known to secrete various metabolism-improving factors, collectively called BATokines, that target various cell types.5)
  • It was widely believed that BAT is present in significant amounts only in newborns, infants and patients with phaeochromocytoma, and that it declines with age in adults becoming rare to detect in those over age 60yrs on PET scans. However, exposure to mild cold (ambient room temperature between 16 and 17°C for 6 weeks) 6)can increase BAT stores in adults especially in the supraclavicular and paraspinal regions, and this may have a role in improving metabolism, insulin sensitivity, and reduce obesity and the “metabolic syndrome”.

shivering if too cold

  • shivering generates heat from high levels of muscle work
  • shivering occurs when the hands or feet get cold and this sends a signal to the brain to commence shivering
  • maximal shivering generally occurs when core temperature reaches 35degC and ceases when it falls below 31degC in which case death is likely to ensue as temperature continues to fall.

exercise if too cold

  • the risk of hypothermia significantly increases when you stop walking

digestion generates heat

  • the process of digesting food generates heat
  • eating food before going to bed (especially if warm as this adds body heat in itself) not only creates heat from digestion but provides energy for shivering

reflective emergency space blankets

  • cheap Mylar ones are crinkly and noisy and not durable, so better options are below
  • SOL 1-2 person heatsheet Emergency Blanket
    • 1.52×2.44m reflective 1mill tarp/blanket
    • 95g $AU15
  • AMK Nano Heat Travel Blanket
    • 170x147cm; 193g; quiet, soft, reflective fabric $AU66
  • SOL Heavy Duty All purpose Emergency Blanket (can be used as tarp)
    • 1.52×2.44m reflective 2.5mill tarp/blanket
    • 223g $AU31 or included in the SOL Emergency Shelter Kit with paracord and pegs for $AU53

thermally insulated sleeping mats

  • avoid thick air mattresses as they tend to drain warmth from you
  • aim for thermally rated sleeping pads

sleeping bag temperature ratings

  • assume sleeping on a sleeping mat and wearing base thermal layers
  • women's bag just use comfort level (comfortable posture and not shivering) if only one quoted
  • men's bags use the colder “lower limit” or “transition” level (curled up but not shivering) if only one quoted
  • “extreme level” is emergency survival only - you will be curled up and shivering even with layers on
  • If a bag is too small, you’ll end up compressing insulation and creating cold spots.
  • if a bag is too big, you spend some of your energy heating empty space. For very cold conditions, many prefer a mummy style bag to reduce empty space at the feet end at the expense of reduced freedom of movement.
  • it’s important not to get a bag that’s too warm; if you sweat, you’ll wake up cold.
  • avoid putting heavy layers on top of a down bag as it will compress the down and lose benefits
  • A +5 to +10 is considered a summer bag. It is roughly as warm as sleeping with a sheet or light blanket over you on your bed at home.
  • A 0 degree bag is a great all-rounder but won’t keep you warm in the snow or frosty night – it’s about the same as having a regular doona on your bed at home.
  • A -5 to -10 degree bag is considered a winter bag for typical Australian climates – it should be similar to having flannelette sheets and an extra blanket or 2 on your bed at home.

sleeping bag liners

  • thin silk or cotton liners may add a few degrees warmth
  • a thermal liner weighing 250g may add an effective 8 degrees to your sleeping bag rating

keeping your tent extra warm on very cold nights

  • use the smallest tent suitable for your needs - it is easier to keep warm
  • use a full fabric tent rather than a mesh tent, especially one with dual fabric/mesh door options
  • choose a sheltered camp site
    • if camping in snow, create a snow wall shelter from the wind
  • position your tent appropriately for the wind direction (although remember it can change overnight!)
  • close the vestibules
    • this will result in the air temperature outside your tent but inside your fly being 0.4-1.4deg warmer than outside and thus creates a better temperature gradient for your tent as well as reducing wind chill and reduce loss of warm tent air through excessive ventilation on windy nights
  • ground insulation
    • consider an extra waterproof ground sheet (eg. tarp) and thermally insulated padding under the tent (eg. foam rubber thick mats)
    • consider using corrugated cardboard as this will also absorb moisture
    • add a space blanket on the tent floor with reflective layer upwards and if possible tape it to the sides of the tent 12-15cm above the floor
  • top insulation
    • add a space blanket
      • duct tape or fasten the blanket all over the top of the inside of your tent with the aluminium of the blanket facing the inside.
    • consider extra one or two waterproof tarps over your tent in addition to the fly
  • wall insulation
    • consider lining walls with space blankets or 10mm bubble wrap (insulating rating of R1 and can also be used above bed)
  • consider a heater
    • a USB heater mat with a power bank will add some valuable warmth to your skin (better still, a 12V car heated cushion at around 2A/hr or a 12V electric blanket - assuming you have an auxiliary 12V battery)
australia/keeping_warm.txt · Last modified: 2024/04/19 09:15 by gary1

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