Heat always flows from warmer to colder – along four paths: through direct contact (conduction), through moving air or water (convection), as invisible infrared radiation (radiation) and through the evaporation of moisture. Almost every technique for keeping warm, cooling down or cooking affects one or more of these paths. Knowing them explains why sleeping pads, windbreaks, emergency blankets and dry clothing work.
This entry explains physics. If there are signs of hypothermia or heat illness, call the local emergency number (112 in the EU).
Four paths of heat transfer
Common mistakes
×Only covering up and forgetting the ground (conduction)
×Underestimating wind protection (convection)
×Treating an emergency blanket as the sole solution (only radiation and wind)
×Sweating heavily in the cold (evaporation)
Limits and risks
–No calculation models or material data
–No substitute for weather and health information
Sources
[1]
David Halliday, Robert Resnick, Jearl Walker – John Wiley & Sons: Fundamentals of Physics
[2]
Wilderness & Environmental Medicine (Wilderness Medical Society) (2019): Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update
Understanding weather fronts: warm front and cold front
A weather front is the boundary between two air masses of different temperature and humidity. At a warm front, warm air slides slowly over cold air – it often announces itself hours ahead with high, thin clouds and brings long-lasting rain. At a cold front, cold air pushes under warm air – the weather changes quickly, with showers, gusts and sometimes thunderstorms. Knowing the signs helps you understand forecasts better and plan more cautiously.
Your own weather observation supplements the official forecast but does not replace it. Before trips, check the forecast and severe-weather warnings from the national weather service.
In the mountains the weather can change locally and very quickly, even without a recognisable front.
Common mistakes
×Dismissing approaching high cloud as harmless
×Relying only on the previous day's forecast
×Ignoring falling air pressure
×Planning a mountain day without a turnaround time
Limits and risks
–No forecasting rules with timings
–No substitute for weather-service warnings
Sources
[1]
U.S. National Weather Service (NOAA): JetStream – An Online School for Weather
[2]
Deutscher Wetterdienst (DWD): Wetter- und Klimalexikon
Thunderstorms need three ingredients: moist air, an unstable atmosphere in which rising air keeps rising, and a trigger such as solar heating, mountains or a cold front. In the towering storm cloud, collisions between ice and graupel particles separate electrical charges – lightning equalises them. Understanding this helps you recognise typical thunderstorm situations earlier and explains why shelter must be sought in good time.
If you can hear thunder, you are within reach of lightning. Immediately seek shelter in a substantial building or a hard-topped metal vehicle and only go back out about 30 minutes after the last thunder.
Thunderstorms can trigger flash floods, even in valleys where it is not raining. Avoid stream beds, gorges and underpasses; never drive or walk through flooded roads.
In the mountains, heat thunderstorms often form in the afternoon. Start trips early and set turnaround times.
Common mistakes
×Waiting until it rains before retreating
×Concluding from the flash-to-thunder interval that you are still safe
×Sheltering under isolated trees
×Moving on immediately after the last flash
Limits and risks
–No detailed behaviour guidance – see the lightning-safety entry
–No details on regional thunderstorm frequency
Sources
[1]
U.S. National Weather Service (NOAA): JetStream – An Online School for Weather
[2]
NOAA National Weather Service (USA): Lightning Safety
[3]
Deutscher Wetterdienst (DWD): Wetter- und Klimalexikon
Wind constantly strips away the warm layer of air next to the skin, so exposed skin cools faster. The wind chill index translates air temperature and wind speed into a feels-like temperature. It describes heat loss and frostbite risk for skin – but wind does not cool objects, water or engines below the air temperature.
In strong wind and cold, cover face, ears, nose and fingers and watch for white, numb patches of skin – they can be signs of beginning frostbite.
Steps
1
Read the index
Weather services often state a feels-like temperature or wind chill in cold weather. It says more about frostbite risk than air temperature alone.
2
Use a wind layer
Even a thin windproof outer layer keeps the warm air inside the clothing and greatly reduces the effect.
3
Cover skin
Face, ears and hands are most affected – wear a hat, neck gaiter and gloves.
4
Seek the lee
Take breaks behind rocks, buildings or in forest; choose a sheltered tent site.
Common mistakes
×Thinking wind chill applies to the temperature of a water container
×Dressing by air temperature only
×Leaving the wind jacket in the pack
Limits and risks
–No table values
–No frostbite treatment
Sources
[1]
NOAA National Weather Service (USA): Wind Chill Chart / Wind Chill Temperature Index
[2]
David Halliday, Robert Resnick, Jearl Walker – John Wiley & Sons: Fundamentals of Physics
Clothing, sleeping bags and pads do not warm by themselves – they trap air. Still air conducts heat poorly and is therefore a good insulator. If the material gets wet, water replaces the air: water conducts heat roughly 20 to 25 times better than air, and as it evaporates it draws extra heat from the body. So: stay dry, adjust layers, avoid cotton in the cold.
Wet clothing in wind and cold can lead to hypothermia, even above freezing. Carry a dry spare layer in waterproof packaging.
Steps
1
Avoid sweating
Remove a layer before climbs, open zips – sweat from inside wets you just as much as rain.
2
Keep rain out
Put on the rain and wind layer in time, before the insulating layer gets wet.
3
Choose material deliberately
In cold and wet conditions use wool or synthetics rather than cotton; keep down dry.
4
Change into dry
At camp swap wet clothing for dry before you cool down.
Common mistakes
×Cotton jeans on cold, wet trips
×Sweating through the insulating jacket under the rain jacket
×Storing the sleeping bag compressed
Limits and risks
–No product values
Sources
[1]
David Halliday, Robert Resnick, Jearl Walker – John Wiley & Sons: Fundamentals of Physics
[2]
The Mountaineers Books (2017): Mountaineering: The Freedom of the Hills, 9th edition
How a compass works: Earth's magnetic field and declination
A compass needle is a small magnet that aligns with the field lines of Earth's magnetic field. It points to magnetic north, not geographic north. The angle between them – declination or variation – depends on location and changes slowly over the years. Iron, magnets and electronics nearby deflect the needle.
Phones, headlamps, knives, cars, fences or power lines can deflect the needle. Keep them away when taking a bearing.
Materials
Baseplate compass
Steps
1
Look up declination
Take the current value for the location from the map (note the year) or an official calculator.
2
Apply the correction
Account for declination when transferring between map and terrain, or use a compass with adjustable declination.
3
Keep interference away
Hold the compass level and keep metal and electronics at a distance.
4
Mind the world zone
When travelling to other continents check whether the needle is balanced for the region, otherwise it may drag.
Common mistakes
×Using declination from an old map without checking
×Taking a bearing next to the car
×Holding a phone right next to the compass
×Holding the compass tilted
Limits and risks
–No declination values
–No complete compass training
Sources
[1]
Headquarters, Department of the Army (USA) (2001): FM 3-25.26 Map Reading and Land Navigation
[2]
U.S. National Oceanic and Atmospheric Administration (NOAA), National Centers for Environmental Information (NCEI): Magnetic Field Calculators (declination calculator)
[3]
David Halliday, Robert Resnick, Jearl Walker – John Wiley & Sons: Fundamentals of Physics
Signals get weaker with distance because their energy spreads over an ever larger area. A whistle carries further than the voice because it produces a loud, high-pitched tone with little effort, in a range where hearing is particularly sensitive. Light needs a clear line of sight but is visible from far away at night and as a reflection of sunlight. Wind, terrain and vegetation shorten both.
Signals complement an emergency call but do not replace it. Where possible call the local emergency number (112 in the EU) first.
Materials
Signal whistle
Signal mirror(optional)
Headlamp / flashlight(optional)
Steps
1
Whistle instead of shouting
Shouting is exhausting and soon makes you hoarse; a whistle stays loud with little breath and stands out from natural sounds.
2
Use patterns
Rhythmic signals (groups of three, the alpine distress signal) stand out from random noise and are understood as distress signals.
3
Choose a position
Signal from open, raised spots, not from hollows or dense forest; consider wind and the noise of streams.
4
Use light deliberately
By day use a mirror with the sun, at night a lamp towards possible helpers; flashing signals attract more attention than steady light.
Common mistakes
×Shouting yourself hoarse
×Signalling from a hollow
×Shouting into a strong wind
×Waving a mirror without aiming
Limits and risks
–No range figures
–No radio or satellite technology
Sources
[1]
David Halliday, Robert Resnick, Jearl Walker – John Wiley & Sons: Fundamentals of Physics
[2]
Headquarters, Department of the Army (USA) (2002): FM 3-05.70 Survival
[3]
European Commission: 112 – the European emergency number
With every metre of height there is less air above us – air pressure falls, to roughly half the sea-level value at around 5,500 m. This has consequences: less oxygen per breath, a lower boiling point of water, and barometric altimeters react to weather changes. Falling pressure often announces worse weather.
Altitude illness can occur at high altitude. With symptoms do not go higher, and descend if things get worse.
Steps
1
Body
Lower oxygen pressure means ascending more slowly so the body can adapt – see high altitude.
2
Cooking
At altitude cooking takes longer and needs more fuel. For water disinfection by boiling, longer boiling times apply at high altitude.
3
Calibrate the altimeter
Reset barometric altimeters at known elevations (summit, hut, map).
4
Watch the pressure trend
If the altimeter rises although you are not climbing (for instance overnight in a hut), pressure is falling – a possible sign of deteriorating weather.
Common mistakes
×Never calibrating the altimeter
×Assuming the percentage of oxygen is lower at altitude
×Using lowland cooking times
Limits and risks
–No exact boiling tables
–No weather forecasting
Sources
[1]
David Halliday, Robert Resnick, Jearl Walker – John Wiley & Sons: Fundamentals of Physics
[2]
U.S. National Weather Service (NOAA): JetStream – An Online School for Weather
[3]
Wilderness Medical Society – Wilderness & Environmental Medicine (2019): Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2019 Update
Warm air can hold more water vapour than cold air. When humid air cools at a cold surface to its dew point, water condenses – as dew, fogging or frost. In a tent, breath, wet clothing and cooking supply the vapour and the cold tent wall supplies the surface. Ventilating, keeping moisture outside and choosing the site wisely reduce the problem.
Do not cook inside a closed tent to dry or warm it – carbon monoxide and fire risk.
Steps
1
Ventilate
Keep vents open even when it is cold; air exchange carries the vapour out.
2
Reduce moisture sources
Leave wet clothing and gear in the vestibule or a bag, do not dry them in the inner tent.
3
Choose the site
Valley hollows and shores collect cold, humid air; slightly raised sites with some air movement are drier. Trees above the tent reduce radiative cooling.
4
Wipe in the morning
Wipe off condensation with a cloth and dry the sleeping bag when possible.
Common mistakes
×Mistaking condensation for a leaking tent
×Closing all vents
×Hanging wet clothing in the inner tent
×Camping in the hollow by the stream
Limits and risks
–No product recommendations
Sources
[1]
Deutscher Wetterdienst (DWD): Wetter- und Klimalexikon
[2]
U.S. National Weather Service (NOAA): JetStream – An Online School for Weather
UV radiation is invisible and cannot be felt, but it causes sunburn, eye damage such as snow blindness and, in the long run, skin cancer. It is strongest around midday, in summer, at altitude and near the equator; snow, water and sand add to it by reflection, and clouds block it only partly. The UV index shows when protection is needed.
On snow, glaciers and water wear sunglasses with UV protection and side shields – snow blindness often appears only hours later.
Cool temperatures or clouds do not mean low UV. Go by the UV index, not by warmth.
Materials
Wide-brimmed sun hat
Steps
1
Check the UV index
Weather services publish the UV index. From moderate values protection is recommended; at high values avoid the midday sun.
2
Shade and clothing
Seek shade, wear a wide-brimmed hat and long sleeves – these protect more reliably than sunscreen alone.
3
Sunscreen
Apply generously to exposed skin and reapply after sweating or swimming.
4
Protect the eyes
Sunglasses with UV protection, with side shields on snow. If lost, improvised slit goggles can help.
Common mistakes
×Skipping protection on cloudy or cold days
×Taking off sunglasses on a glacier
×Forgetting chin, ears and neck
×Applying sunscreen only in the morning
Limits and risks
–No product recommendations
–No medical advice
Sources
[1]
World Health Organization (with WMO, UNEP and ICNIRP) (2002): Global Solar UV Index: A Practical Guide
Satellite navigation measures how long radio signals from several satellites take to reach the receiver and calculates the position from that. Under open sky it is accurate to within a few metres. In gorges, between tall buildings, under dense forest and with a flat battery it becomes inaccurate or fails. GPS therefore does not replace a map, compass and battery planning.
Battery, cold, reception or a fall can make the device fail at any time. Always carry a paper map and a compass and practise using them.
Altitude from satellite signals is usually less accurate than horizontal position. For height, rely more on the map and contour lines.
Materials
GPS unit(optional)
Mobile phone(optional)
Topographic map
Steps
1
Clear view of the sky
For a good fix, move to an open spot, hold the device up and wait briefly until the displayed accuracy is stable.
2
Download maps for offline use
Positioning works without mobile coverage, but the phone's map often does not. Download maps before the trip.
3
Check plausibility
If the position jumps, compare the display with the terrain and the map. In gorges and cities expect errors of many metres.
4
Plan power
Airplane mode with location still on saves battery; keep the device close to your body in the cold and carry a power bank.
5
Pass on coordinates
In an emergency, read out the coordinates in the agreed format and pass them on to rescuers.
Common mistakes
×Following the position display blindly
×Not having downloaded an offline map
×Not watching the battery level
×Thinking the altitude reading is exact
×Mixing up coordinate formats
Limits and risks
–No device or app recommendations
–No exact accuracy figures for specific devices
Sources
[1]
National Coordination Office for Space-Based Positioning, Navigation, and Timing (USA): GPS.gov – Official U.S. government information about the Global Positioning System and related topics
[2]
David Halliday, Robert Resnick, Jearl Walker – John Wiley & Sons: Fundamentals of Physics
Understanding electricity: voltage, current and why water conducts
What is dangerous is the current that flows through the body. How much flows depends on the voltage and the resistance – and wet skin, water and earth greatly lower the resistance. That is why mains voltage in the home, flooded basements and fallen power lines are deadly, while a torch battery is harmless.
Always treat fallen or damaged power lines as live. Keep well away, warn others and call the grid operator or the local emergency number (112 in the EU).
Never enter a flooded room while the power there could still be on. Only switch off the supply if the fuse box can be reached dry and safely – otherwise call professionals or the fire service.
Do not touch a person who is in contact with electricity until the power has been switched off. Otherwise you become part of the circuit yourself. Call emergency services.
Work on household wiring is for qualified electricians; what laypeople may do differs between countries – check local rules.
Steps
1
Respect mains voltage
Mains voltage is 230 volts in Europe and 120 volts in North America – both can be fatal. Do not operate appliances with wet hands or while standing in water.
2
Know your protective switches
Residual current devices (RCDs) switch off when current leaks via the wrong path. Test them regularly with the test button.
3
Keep your distance outside
Stay away from damaged lines, pylons and substations; never fly kites or use fishing rods near overhead lines.
4
Connect generators safely
Never feed a generator directly into household wiring except via a professionally installed transfer switch – otherwise back-feeding endangers line workers.
Common mistakes
×Assuming a fallen line is switched off
×Wading into a flooded basement to switch off the fuses
×Touching a person in contact with a power source
×Leaving extension leads lying in water
Limits and risks
–No instructions for electrical installation
–No medical treatment after electrical accidents
Sources
[1]
David Halliday, Robert Resnick, Jearl Walker – John Wiley & Sons: Fundamentals of Physics
[2]
U.S. Federal Emergency Management Agency (FEMA): Are You Ready? An In-Depth Guide to Citizen Preparedness
[3]
European Commission: 112 – the European emergency number
Friction in rope: why knots and friction hitches hold
A knot does not hold by magic but by friction: under load the turns press against each other, and every additional wrap multiplies the holding force. This explains why a round turn holds a load almost on its own, why friction hitches grip under tension and slide when unloaded – and why slippery rope holds knots less well.
This knowledge explains principles. Life-critical belays require training, certified equipment and proven knots.
Materials
Paracord(optional) – For the experiment
Steps
1
Experiment: wraps
Wrap a cord once, twice, three times around a smooth pole and pull on one end while holding the other loosely. With each wrap you need less holding force.
2
Dress and set the knot
A neatly dressed, firmly set knot has defined nips; a messy one can capsize or slip under load.
3
Leave long enough tails
Under varying load, rope can creep through a knot. Long tails provide a reserve.
4
Watch out for slippery material
Slippery, stiff or very thin cords have less friction. Choose knots with more turns or an extra backup for them.
Common mistakes
×Not setting knots tight
×Leaving tails too short
×Using the same knots for slippery synthetics as for natural fibre
×Tying friction hitches with cord as thick as the rope
Limits and risks
–No strength figures
–No instructions for climbing or rescue technique
Sources
[1]
David Halliday, Robert Resnick, Jearl Walker – John Wiley & Sons: Fundamentals of Physics
[2]
Clifford W. Ashley – Doubleday, Doran & Co. (1944): The Ashley Book of Knots
[3]
Geoffrey Budworth (1997): The Complete Book of Knots
The breaking strength on the label applies to a new, straight rope under slow loading. In use, a rope is almost always weaker: knots and sharp bends, edges, abrasion, sunlight, heat, chemicals and age all cost strength, and sudden loads are many times the weight. That is why people work with large safety margins.
To secure people, use only rope and equipment tested and certified for that purpose – with training. Never use paracord, washing line or unknown ropes for people.
Shock loads, such as a falling object or a snatching tow rope, can reach many times the static weight. When towing or hauling, keep away from tensioned ropes.
Materials
Rope
Paracord(optional)
Steps
1
Allow a safety margin
Never load a rope anywhere near its stated breaking strength. For many ropes, manufacturers specify a much lower working load.
2
Soften edges and bends
Do not run ropes over sharp edges; use edge protection made of cloth or hose and choose large radii.
3
Inspect regularly
Run the rope through your hands: hard, soft or thin spots, glazed areas from heat, damaged sheath, discolouration. When in doubt, retire it.
4
Store correctly
Store dry, dark and cool, away from chemicals such as battery acid and solvents; dry the rope and remove grit before storing.
Common mistakes
×Treating the label value as working strength
×Running rope over rock or metal edges
×Leaving rope in the sun for years
×Running rope over rope
×Using unknown rope for loads above people
Limits and risks
–No strength figures
–No standards for climbing or lifting gear
Sources
[1]
The Mountaineers Books (2017): Mountaineering: The Freedom of the Hills, 9th edition
[2]
Geoffrey Budworth (1997): The Complete Book of Knots
How fast and in which direction a fire spreads is determined by three factors: fuel, weather and terrain. Wind and slope tilt the flames onto unburnt material and preheat it; fine, dry fuels ignite most easily. Understanding this helps you choose fire sites better and recognise why vegetation fires escalate so suddenly.
Fires run considerably faster uphill than on the flat, especially in gullies and ravines. Never flee uphill ahead of a fire; leave early and call the local emergency number (112 in the EU).
Wind carries embers and sparks, sometimes far ahead of the flame front, starting new fires there. Even a seemingly small campfire in wind is a risk – observe fire bans.
Steps
1
Read the fuel
How fine, dry and continuous is the vegetation? Dry grass, leaves and needle litter accelerate ignition; wet soil and rock slow it down.
2
Read the weather
Pay attention to wind, humidity and temperature. Gusty and shifting wind, for example ahead of thunderstorms, is especially dangerous.
3
Read the terrain
Slopes, gullies and saddles act like chimneys. Sun-facing slopes are usually drier.
4
Apply it to your fire site
Place a fire on mineral soil, sheltered from wind, not at the foot of a vegetated slope, with distance from trees and overhanging branches.
Common mistakes
×Lighting a fire in wind
×Placing a fire at the foot of a slope under dry vegetation
×Underestimating flying embers
×Ignoring afternoon heat and dryness
Limits and risks
–No spread rates
–No firefighting
Sources
[1]
Stephen J. Pyne, Patricia L. Andrews, Richard D. Laven – John Wiley & Sons (1996): Introduction to Wildland Fire (2nd edition)
[2]
Deutscher Wetterdienst (DWD): Waldbrandgefahrenindex (WBI)
https://www.dwd.de
[3]
European Commission: 112 – the European emergency number
Reading clouds and understanding weather forecasts
Clouds show what is happening in the atmosphere: heap clouds that grow rapidly upwards announce showers and thunderstorms; thickening veil clouds often a front. An official forecast is still the better basis – watching clouds serves as an on-site check of whether the weather is arriving faster than forecast.
Towering clouds with dark bases, thunder or lightning: switch to thunderstorm safety immediately and leave exposed ridges and water. Weather rules from clouds do not replace warnings from weather services.
Steps
1
Get the forecast
Before the trip read the forecast and warnings from the national weather service, especially thunderstorm and wind warnings.
2
Understand probabilities
A chance of rain says how likely precipitation is, not how long or how heavily it will rain. In thunderstorm situations, place and time are especially uncertain.
3
Watch the sky
Look up regularly on the way: are heap clouds already growing tall in the morning? Is the veil getting thicker and the cloud base lower?
4
Decide in time
Set turnaround points and alternative routes in advance and turn back earlier than planned at signs of deterioration.
Common mistakes
×Putting folk weather rules above official forecasts
×Only checking the weather in the morning
×Ignoring towering clouds because the sun is still shining
×Reading chance of rain as rain duration
Limits and risks
–No forecast for specific places
–No identification key for all cloud species
Sources
[1]
World Meteorological Organization (WMO): International Cloud Atlas
[2]
U.S. National Weather Service (NOAA): JetStream – An Online School for Weather
[3]
Deutscher Wetterdienst (DWD): Wetter- und Klimalexikon
Whether a night is bright or pitch dark depends greatly on the moon: at full moon it is in the sky all night, at new moon not at all. Knowing the moon phase lets you judge whether anything can be seen without a lamp, when the moon will rise and why a night walk is easy one week and difficult the next.
Even bright moonlight is not enough to safely see steps, roots or drop-offs. Always carry a lamp and spare batteries.
Materials
Headlamp / flashlight
Steps
1
Look up the moon phase
Look up the moon phase and moonrise for the date in a calendar, weather app or astronomical service.
2
Plan night activity
For night walks or early starts, use the days around full moon and allow for sections in moon shadow (shaded slopes, forest).
3
Let your eyes adapt
The eyes take about half an hour to adapt largely to darkness. Bright light destroys the adaptation quickly; use a dimmed lamp.
4
Rough direction
Like the sun, the moon is roughly in the east when it rises and in the west when it sets. For finding direction this is only a rough aid.
Common mistakes
×Relying on moonlight instead of a lamp
×Assuming moonrise coincides with sunset
×Not allowing for cloud and forest
×Destroying dark adaptation with bright screens
Limits and risks
–No detailed moon navigation
–No brightness values
Sources
[1]
U.S. Naval Observatory: Astronomical Applications Department – sun and moon data, phases of the moon
[2]
David Halliday, Robert Resnick, Jearl Walker – John Wiley & Sons: Fundamentals of Physics
The moon and sun pull with different strength on different parts of the Earth. This creates two tidal bulges beneath which the Earth rotates – on many coasts two high and two low waters a day, about 50 minutes later each day. How large the difference is depends heavily on the shape of the coast. Hence the rule: read the tide table for exactly that place.
Incoming water can cut off coves, headlands and sandbanks faster than expected. Check the tide table, start back before low water, walk mudflats only with a local guide. If cut off, do not wade back through deep water – call the local emergency number (112 in the EU).
Wind and air pressure can change the water level considerably compared with the table. In storms, the authorities' warnings apply.
Steps
1
Tide table for the place
Take the high and low water times for the nearest reference port from official tide tables.
2
Note the moon phase
Around new and full moon, high waters are higher and low waters lower – more exposed flats but also faster-rising water.
3
Allow a buffer
Plan the return so you are back long before the tide comes in. Wind and air pressure can bring the water earlier.
4
Observe on site
Channels, gullies and low spots fill first. If you see water running behind you, turn back immediately.
Common mistakes
×Using the tides of another place
×Assuming high water comes at the same time every day
×Not allowing for spring tides
×Wading back through filling channels
Limits and risks
–No tide calculation for specific places
–No boat navigation
Sources
[1]
U.S. National Oceanic and Atmospheric Administration (NOAA) – National Ocean Service: Tides and Water Levels (NOAA Ocean Service Education tutorial)
[2]
David Halliday, Robert Resnick, Jearl Walker – John Wiley & Sons: Fundamentals of Physics
[3]
European Commission: 112 – the European emergency number
19 · Chemistry and biology · Expert review pending
Why boiling disinfects water
Heat damages the proteins, membranes and genetic material of microorganisms so badly that they can no longer multiply or cause disease. How quickly that happens depends on temperature and time. A rolling boil is far above what most waterborne pathogens can survive – which is why it is regarded as very reliable. Heat does not help against chemicals and salt, however.
For practical use, follow health authority guidance on boiling water, see the entry “Boiling water”. Follow instructions when a boil-water advisory is issued.
Boiling does not remove chemicals, heavy metals or salt; some substances even become more concentrated as water evaporates. If chemical contamination is suspected, use another water source.
Never operate stoves or fires in tents, vehicles or enclosed spaces without adequate ventilation (carbon monoxide).
Common mistakes
×Mistaking the first bubbles at the bottom for boiling
×Pouring boiled water into dirty containers
×Assuming boiling removes chemicals
×Confusing boiling with sterilisation
Limits and risks
–No separate practical instructions – see the entry “Boiling water”
–No details on individual pathogens
Sources
[1]
World Health Organization (2015): Boil water – Technical brief
[2]
Centers for Disease Control and Prevention: Making Water Safe in an Emergency
[3]
World Health Organization (2022): Guidelines for drinking-water quality, fourth edition incorporating the first and second addenda
20 · Chemistry and biology · Expert review pending
What happens in combustion
Wood does not burn directly: heat first breaks it down into flammable gases (pyrolysis), and these gases burn in the flame with oxygen from the air. What remains is charcoal, which glows without a flame. If oxygen is lacking or the fire is too cool, combustion is incomplete – producing smoke, soot and carbon monoxide. The fire triangle of fuel, oxygen and heat sums up what a fire needs.
Any combustion in enclosed spaces can produce carbon monoxide. No barbecues, stoves or fires in tents, living spaces or garages.
Open fires are restricted or banned in many places – check local rules and the fire danger.
Steps
1
Fire triangle
Fuel, oxygen and heat must come together. Remove one and the fire goes out – extinguishing is based on this too.
2
Pyrolysis and flame
The flame is burning gas above the wood. That is why a fire burns better when air reaches it from below and between the pieces.
3
From thin to thick
Tinder and thin kindling provide enough heat to pyrolyse thicker wood – which explains the structure of every fire lay.
4
Read the smoke
Lots of white to grey smoke often indicates damp wood or a fire that is too cool; a hot fire with good airflow smokes less.
Common mistakes
×Adding thick wood too early
×Smothering the fire by packing it too tightly
×Using accelerants
×Heating or cooking with an open flame in enclosed spaces
Limits and risks
–No fire safety consulting
Sources
[1]
Headquarters, Department of the Army (USA) (2002): FM 3-05.70 Survival
[2]
David Halliday, Robert Resnick, Jearl Walker – John Wiley & Sons: Fundamentals of Physics
[3]
World Health Organization, Regional Office for Europe (2010): WHO guidelines for indoor air quality: selected pollutants (carbon monoxide chapter)
21 · Chemistry and biology · Expert review pending
Carbon monoxide: why it is so dangerous
Carbon monoxide (CO) forms when fuel burns incompletely. It is colourless, odourless and tasteless and binds far more strongly to the blood's red pigment than oxygen does. As a result the body suffocates from within, often without the person noticing. Protection: never burn anything in enclosed spaces, use CO alarms, and if you suspect it get into fresh air immediately and call for help.
If carbon monoxide is suspected (headache, dizziness, nausea, drowsiness in several people, CO alarm sounding): get everyone into fresh air immediately, do not re-enter and call the local emergency number (112 in the EU).
Never run barbecues, charcoal, gas stoves, unflued heaters or generators in living spaces, basements, garages, tents or vehicles – not even with a window open.
Materials
Carbon monoxide alarm
Steps
1
Know the sources
Stoves, boilers, fireplaces, barbecues, camping stoves, generators, vehicle engines – every flame and every combustion engine.
2
CO alarm
Install and test CO alarms according to the manufacturer in rooms with fuel-burning appliances. A smoke alarm does not detect CO.
3
Take signs seriously
Headache, dizziness, nausea, tiredness – especially if several people or pets are affected at once and it improves outdoors.
4
Get out and call
Get into fresh air immediately, call for help and have the fire service or professionals check before returning.
Common mistakes
×Relying on smell
×Bringing a barbecue indoors for heating
×Running a generator in the garage with the door open
×Using a stove in a closed tent
Limits and risks
–No medical treatment
–No limit values
Sources
[1]
World Health Organization, Regional Office for Europe (2010): WHO guidelines for indoor air quality: selected pollutants (carbon monoxide chapter)
[2]
Centers for Disease Control and Prevention: Carbon Monoxide Poisoning – Prevention guidance
[3]
John E. Hall – Elsevier: Guyton and Hall Textbook of Medical Physiology
[4]
European Commission: 112 – the European emergency number
22 · Chemistry and biology · Expert review pending
Batteries in the cold
In a battery, chemical reactions supply the current. Cold slows these reactions and raises internal resistance – devices switch off early even though energy is still stored. Once warmed up the battery usually recovers. Lithium-ion batteries should not be charged below freezing. Carry spare batteries close to the body and take devices into the sleeping bag at night.
Never warm batteries with fire, a stove or hot air and do not use damaged or swollen batteries – fire and explosion risk.
Do not charge lithium-ion batteries below freezing; let them reach room temperature first. Manufacturer instructions take precedence.
Materials
Spare batteries
Power bank(optional)
Headlamp / flashlight
Steps
1
Carry close to the body
Carry the phone, spare batteries and power bank in an inside pocket; take them into the sleeping bag at night.
2
Swap rather than discard
Swap cold, apparently empty batteries for warm ones and rewarm the cold ones on your body – they often still deliver power.
3
Choose chemistry deliberately
Choose battery types suitable for cold according to the manufacturer; check the device manual for permitted types.
4
Avoid condensation
Bring cold devices into warm rooms in a sealed bag and let them warm up slowly there.
Common mistakes
×Throwing away cold batteries as empty
×Warming a battery at a stove
×Charging in a tent in frost
×Carrying the phone in an outer pocket
Limits and risks
–No product or run-time figures
Sources
[1]
Thomas B. Reddy (ed.) – McGraw-Hill: Linden's Handbook of Batteries
23 · Chemistry and biology · Expert review pending
Microbes in food: spoilage, fermentation and safety
Bacteria, yeasts and moulds need water, nutrients, a suitable temperature and, depending on the type, oxygen or its absence. Preserving food means taking one of these conditions away: cooling, drying, salting, acidifying, heating. Fermentation uses desirable microbes that produce acid and thereby crowd out undesirable ones – it only works reliably with tested recipes.
The bacterium Clostridium botulinum can produce a deadly toxin in airtight, low-acid foods at room temperature – often without any visible change. Use only tested recipes and methods for canning and preserving.
Bulging lids, gas in non-fermented preserves, unusual smells or mould: do not taste, throw it away. If poisoning is suspected, call the local emergency number (112 in the EU).
Materials
Fermentation jar or crock(optional)
Steps
1
Understand the cold chain
Keep perishable food cold or keep it hot – do not leave it for hours in the range in between.
2
Acid as protection
Pickled and lacto-fermented foods are safer because the acid inhibits pathogens. The necessary acidity comes from the recipe, not from taste.
3
Use tested methods
Can low-acid foods such as vegetables, meat and beans only according to tested instructions; when fermenting, stick to the salt quantity and temperature.
4
Work cleanly
Keep hands, jars and work surfaces clean – fewer unwanted microbes at the start mean a lower risk.
Common mistakes
×Changing recipes by feel
×Canning low-acid vegetables without a tested method
×Tasting suspicious preserves
×Leaving cooked food standing warm for hours
Limits and risks
–No recipes
–No identification of moulds or pathogens
Sources
[1]
World Health Organization (WHO) (2006): Five Keys to Safer Food Manual
[2]
United States Department of Agriculture (USDA) – National Institute of Food and Agriculture: Complete Guide to Home Canning
[3]
University of Georgia / National Center for Home Food Preservation (USA): National Center for Home Food Preservation – tested guidance on drying and preserving food
[4]
European Commission: 112 – the European emergency number
A large part of the body is water, and the body constantly loses water through breathing, skin, sweat and urine. Thirst and concentrated urine are the signals it uses to counteract this. In heat, exertion, cold, altitude, diarrhoea or vomiting, losses can outpace replacement. This entry explains the basics – it is not a treatment guide.
In case of confusion, reduced consciousness, fainting, no urine for many hours, or persistent vomiting and diarrhoea – especially in children, older and sick people – call the local emergency number (112 in the EU) or get medical help.
Too much water can also be harmful: drinking very large amounts of plain water during long exertion while taking in little salt can cause a dangerous sodium deficiency. Drink according to thirst and need, not “as much as possible”.
Drink only safe or treated water; diarrhoea from contaminated water makes fluid loss worse.
Common mistakes
×Ignoring thirst in the cold or at altitude
×Only drinking once very thirsty
×Counting alcohol as fluid
×Drinking only large amounts of plain water and eating nothing during long exertion
Limits and risks
–No diagnostic or treatment guidance
–No fluid quantities for heat or sport
Sources
[1]
John E. Hall – Elsevier: Guyton and Hall Textbook of Medical Physiology
[2]
World Health Organization: Heat and health (fact sheet)
Sweating only cools when the sweat evaporates. In high humidity it evaporates poorly – which is why muggy heat feels hotter and is more dangerous than dry heat at the same temperature. The heat index combines temperature and humidity into a feels-like temperature.
Confusion, reduced consciousness or a seizure in heat are an emergency: call the local emergency number (112 in the EU).
Heat index values generally apply to shade. In direct sun the strain is higher.
Steps
1
Note the feels-like temperature
Weather services often give a heat index or feels-like temperature in heat; heat warnings take humidity into account.
2
Adjust exertion
In muggy weather slow down, rest in the shade and do strenuous work in the cooler parts of the day.
3
Drink regularly
Replace lost water, even if sweat does not visibly evaporate.
4
Help evaporation
Loose, airy clothing, air movement from a fan or wind, moistening the skin.
Common mistakes
×Looking only at the temperature
×Planning muggy days like dry days
×Assuming sweating always cools
Limits and risks
–No table values
–No treatment
Sources
[1]
NOAA National Weather Service (USA): Heat Index (heat safety information)
[2]
John E. Hall – Elsevier: Guyton and Hall Textbook of Medical Physiology
[3]
Wilderness & Environmental Medicine (Wilderness Medical Society) (2019): Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Heat Illness: 2019 Update
The body keeps its core temperature within a narrow range. If it loses more heat than it produces, it first reduces blood flow to the skin and limbs and starts to shiver. When the core temperature falls below 35 °C, this is called hypothermia: thinking, coordination and eventually consciousness decline. Recognise it early, protect from further heat loss and get help.
With confusion, marked drowsiness, reduced consciousness or if shivering stops while the person is still cold: call the local emergency number (112 in the EU). Handle the person gently and protect from the cold.
Hypothermia can also develop above freezing – through wetness, wind, exhaustion or cold water.
Steps
1
Early signs
Shivering, cold hands, feeling cold, declining fine motor skills. A well-known memory aid: stumbles, mumbles, fumbles, grumbles.
2
Stop heat loss
Get out of wind and wet, swap wet clothing for dry, insulate – including from the ground – and cover the head.
3
Provide energy
If the person is awake and can swallow safely, warm sweet drinks and food help generate heat.
4
Get help
With warning signs or if the condition does not improve, call for help and protect from the cold until help arrives.
Common mistakes
×Trusting the hypothermic person's own judgement
×Carrying on in wet clothing
×Expecting hypothermia only in frost
×Giving drinks to people with reduced consciousness
Limits and risks
–No treatment of severe hypothermia
–No resuscitation instructions
Sources
[1]
Wilderness & Environmental Medicine (Wilderness Medical Society) (2019): Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update
[2]
John E. Hall – Elsevier: Guyton and Hall Textbook of Medical Physiology
[3]
European Commission: 112 – the European emergency number