heat injury, burns, heat rashes and heat illness

see also:

• keeping warm when camping or hiking
• risk management when camping
• hot water and showers for campers
• gas or liquid fuel stoves for camping
• wood stoves for camping
• 12V heating pads / "electric blankets" to lie on
• first aid kits for camping and hiking

• injury or illness from excessive or prolonged heat is a significant risk to campers
• PREVENTION IS FAR BETTER THAN CURE!!!!
  • don't hike or camp on extreme weather days (bushfires are an added risk to heat stroke!)
  • drink plenty of water on warm days especially if hiking
  • ensure adequate sun protection
  • wear heat protective gloves when managing wood stoves or camp fires
  • ensure flammable clothes, tents, etc are well away from flames
  • ensure trip hazards are not present around camp fires or stoves
  • don't light open wood fires on windy days as embers will go everywhere perhaps including your flammable tent
  • don't get drunk around camp fires or stoves
  • always have 10L water close at hand around camp fires or wooden stoves
  • avoid drinking very hot drinks in case they spill - add cold water or cold milk
• BRING FIRST AID JUST IN CASE!!
  • Glad Wrap is an important option for large severe burns
  • Burn Shield or similar product is useful
  • see also: first aid kits for camping and hiking

• hot ambient temperatures
  • may cause dehydration, heat rashes, heat illness, heat stroke
• sun exposure
  • may cause dehydration, sunburn, etc
• direct contact with very hot camping equipment - stoves, cookware
  • these are likely to cause 3rd degree burns and if it is a large area, may require skin grafting
  • tip: use a piece of wood to close the stove door when its dark - there is a high chance you will touch the door not the handle otherwise and that could be a 3rd degree burn!
• scald burns from boiling water
• direct prolonged contact with moderately hot camping gear - electric blanket, hot water bottle, etc
• flame burns from direct contact
  • camp fire flames
  • clothes or tent catching fire
  • gas circuit catching fire
  • gas stove falling over
  • these will cause 3rd degree burns needing skin grafting if it is a large area
• convective heat exposure:
  • trapped inside a caravan on fire
  • convective heaters being too close (not usually available whilst camping unless one has a powered site)
• radiant heat exposure from being too close to a camp fire or stove
  • a particular risk for dogs sleeping in front of a stove

• the severity of these burns depends upon contact time and the temperature of the heat source as well as the thickness of skin at the site
• thermal skin burns will not occur with heat sources below 44°C
  • however, prolonged heat below 44°C may still cause heat rashes as below
  • between 44 °C and 51 °C at the skin surface, the rate of thermal injury doubles with each degree increase in temperature
  • skin temperature above 51 °C will cause almost immediate destruction of the epidermis (1st degree burn)
• above 70 °C, full-thickness tissue destruction occurs in seconds (Arturson, 1996)
• very hot objects over 100degC such as a wood stove will cause IMMEDIATE deep full thickness 3rd degree burns
• sleeping on a hot water bottle or a folded electric blanket / throw rug may cause significant burns as these can easily be over 44degC
• the following chart from experiments by Moritz and Henriques (1947) clearly show the importance of this relationship

• heat injury due to hot air
• for unprotected human skin there appears to be a limit of about 120°C (248°F) for convected heat, above which there is, within minutes, onset of considerable pain along with the production of burns.
• convective heat below this level may cause hyperthermia, dehydration and heat illness
• if in a building on fire, excluding other factors such as radiant heat, flames, carbon monoxide poisoning and other toxins,
  • can tolerate convective heat for ~4minutes without becoming incapacitated at 75-80degC
  • can tolerate convective heat for ~8minutes without becoming incapacitated at 65degC
  • can tolerate convective heat for ~14minutes without becoming incapacitated at 55degC
• thermal burns to the respiratory tract from inhalation of air containing less than 10 percent by volume of water vapor do not occur in the absence of burns to the skin or the face;
• thermal burns to the respiratory tract can occur upon inhalation of air above 60°C (140°F) that is saturated with water vapor (ie inhalation of steam)

• fires emits high levels of invisible infrared light that travels as with visible light through the air.
  • intensity follows the inverse square law - drops by a quarter as the distance is doubled
    • hence flammable materials should generally be at least 1.5m from a stove
  • radiant heat from a bare flame:
    • open fires tend to give off 30% of their total heat output as radiant heat
    • radiant heat flux = SEP x view factor x τ
      • surface emissive power (SEP) of the flame - dependent upon clarity of the flame, which is influenced by the reactivity of the fuel, the access of oxygen, and the amount of soot produced, examples:
        • hydrocarbon pool with small flame: SEP = 100 kW/m²
        • larger hydrocarbon pool with larger flame (and more soot): SEP = 50 kW/m²
        • methane (LNG) contains four hydrogen atoms and burns as a blue flame: SEP = 150-200kW/m²
        • BLEVE fireballs SEP = 300-350kW/m²
      • view factor is dependent upon:
        • the orientation of the flame and its size
        • the orientation of the receiving surface in relation to the flame
        • the distance of receiving surface from the flame
      • τ = radiation transmissivity of the air - water content, distance
    • radiant heat for people standing around a hydrocarbon pool fire
      • heat flux = 15.4 x ( (distance from edge of fire + diameter of fire/2)/diameter of fire)^-1.59
        • where heat flux in kW/m², distances are in metres, and may need to multiply by 2 for variability
        • only applies when ( (distance from edge of fire + diameter of fire/2)/diameter of fire) > 0.7 and < 15
  • when these waves hit an object or a person, the radiant energy is absorbed and converted into heat.
  • combustion of flammable materials via radiant heat
    • when radiant heat is absorbed by a combustible material, the object catches fire when the material’s ignition temperature is reached.
    • Flaming ignition of a solid material requires chemical decomposition and the ensuing production of flammable vapors. These vapors will ignite if certain criteria are met.
      • First, the gases must be in a concentration with sufficient fuel (flammable vapors) and oxygen content, defined by the lower and upper flammability limits.
      • Second, the activation energy for combustion must be supplied either by an ignition source (piloted ignition), or by localized heating of the gases above the autoignition temperature (spontaneous ignition)
    • Heterogeneous combustion (i.e. smoldering ignition) at the solid-fluid interface is also possible for some materials such as many cellulose-based materials (paper, wood,fiberboard, etc.) and some expanded thermoset plastics
    • The critical heat flux is defined as the minimum heat flux required either for piloted or spontaneous ignition. It is equal to the heat loss from the surface at ignition because below this irradiance level the surface temperature can never reach the ignition temperature. This is also dependent upon ambient temperature and the thickness of the material.
  • exposed individuals quickly feel unbearable pain, followed by second-degree burns if the intensity is high
  • similar to thermal burns, skin injury is dependent upon intensity and exposure time
    • fire fighters are commonly exposed to levels around ~ 130 kW/m² in standard fire hazard (structural fire or bush fire) and require radiant heat protective clothing and face/hand protection
    • even prolonged exposure at levels < 20 kW/m² wearing protective clothing may cause burns
    • campers will often develop corneal eye and lip minor burns after a night sitting around the campfire (some of the eye soreness also relates to smoke and possibly ash)
• Stoll curve to predict partial thickness skin burns
  • developed by Alice Mary Stoll, an American biophysicist who developed fire-resistant clothing
  • determined the time it takes for second degree burn damage to occur on bare skin for a given heat flux exposure (corneal injury occurs in around half this time):
    • exposure time to partial thickness burn in seconds = 1.3 * H^-1.43 (for H > 0.1)
      • H = heat flux in cal/cm²/sec
      • 1 cal/cm²/sec = 42 kW/m²
      • 1 BTU/foot²/min = 0.19 kW/m²
    • exposure time to partial thickness burn in minutes = 106 * Q^{-1.35 1)}
      • where Q = radiant heat flux in kW/m²
• time to pain for exposed skin
  • = safety factor coeff x (35/Q)^{1.33 2)}
    • safety factor coeff = 0.5 for Q < 6 and 0.25 for Q > 6
    • Q = radiant heat flux in kW/m²
• pain tenability limit for bare human skin is 1.7 kW/m²
  • some use a value of 2.5 kW/m² and suggest values below this can be tolerated for 30 minutes or longer without significantly affecting the time available for escape

• these are generally due to prolonged sweating in hot, humid conditions such as:
  • tropics, especially if not acclimatised
  • hiking in hot weather
  • wearing clothing that it too warm / constrictive / non-breathable for the activity and ambient temperature
  • sleeping in excessively warm conditions such as:
    • wearing clothes in sleeping bags that are too insulating for the conditions
    • excessive high temperatures of electric blankets
  • febrile illness may also be a factor
• the main types of rashes are:
  • chaffing esp, in groin, between thighs
  • prickly heat rash
  • tinea cruris (a fungal infection of the groin)
  • Grover's disease - mainly middle aged people whose skin is sun damaged and does not perspire well