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heat injury, burns, heat rashes and heat illness

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  • AVOID SERIOUS CAMPFIRE BURNS - NEVER use water to put out your vegetable oil fuelled campfire!
    • reduce risk of oil igniting by:
      • use a cooking oil with higher flash point such as safflower oil (smokepoint 265degC compared with sunflower oil 225degC and extra virgin olive oil at only 165-190degC)
      • reduce heat or remove the pan if the oil starts smoking as this means it is getting close to its flashpoint
      • ensure oil does not drip onto floor of your camp oven which may be well over 300degC!
    • ensure you keep it away from flammable materials
    • have a fire blanket and extinguisher designed for oil fires on hand
  • hot days without adequate water and shade can lead to confusion and then death - even in young people
    • a 37 yr old lady died after leaving her car getting lost hiking in the Northern Territory, Australia in October 2023 when temperatures approached 50degC
    • it is usually best to stay with your car - you will be more easily found


  • injury or illness from excessive or prolonged heat is a significant risk to campers
    • 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

Sources of injury

  • 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

Thermal contact skin burns

  • 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
heated metal pipe temperature: 45°C 50°C 55°C 60°C 65°C
contact time to cause partial thickness burn: 3hrs 4 min 30sec 5sec 1 sec

Convective heat injury

  • 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)

Radiant heat injury

  • 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
heat flux kW/m2 2 4 10 30-40 80-90
bare skin exposure time to scorching pain or corneal injury 40-60secs 20secs 5secs 0.25sec
bare skin exposure time to partial thickness burn 80-120secs 35-40secs 10secs 0.5sec
combustion of wood piloted ignition at 12.5 auto ignition 5-10min at 20, 1-2min at 30 for 15-20mm chipboard or softwood
clothing protection of skin plastics melts at 13 cotton ignites in secs at 40 PPE for fires rated around 80
building materials glass fails at 120°C and 4; many furniture materials ignite at 7 after 2-3min giving 250-300°C3); wood/plastics combust at 400°C and 15 steel fails at 500°C and 100
heat source radiant heat flux kW/m2
solar sunny day 1 (< 1.7 the bare skin tolerable limit but there are also UV rays to cause delayed sunburn!)
standing 1m from edge of a 1m camp fire 1.5-4 depending upon amount of flames
standing 3m from edge of a 1m diameter hydrocarbon pool fire 2-4
standing 2m from edge of a 1m diameter hydrocarbon pool fire 3.5-7
standing 2m from edge of a 1.5m diameter hydrocarbon pool fire 6-10
standing 1m from edge of a 1m diameter hydrocarbon pool fire 8-16
woodland bushfire at 35m 10
10m or taller forest bushfire at 50m4) 10
ceiling smoke in a house fire at 200-500°C 1-20
flame from 5mx2m shrub fire at 3m 20
flame from 10mx15m tree fire at 10m 40
flame from 5mx15m tree fire at 3m 50
flame from 30mx20m tree fire at 10m 80
3 phase 600V AC power may give a 1000A arc flash lasting 1 sec at 20inches 5) 90
flame from 10mx15m tree fire at 3m 100
flame from 30mx20m tree fire at 3m 110
nuclear bomb air burst duration of 1 sec >100

Heat rashes

  • 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
australia/heat_injury.txt · Last modified: 2023/10/30 16:50 by gary1

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