chapter 5 environment and performance - us forest … 5— environment and performance 34 heat...

Chapter 5—Environment and Performance

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Anumber of environmentalfactors influence workoutput. This chapterfocuses on heat stress,altitude, and smoke, the

ways they affect performance andthreaten health, and the things you cando to minimize their impact.

Heat StressField work is often demanding. But it’seven tougher when you’re hiking asteep slope with a heavy load in theheat, under a glaring sun. Wildlandfirefighting is hot, physicallydemanding work, so it’s vital that youunderstand heat stress, how it affectsyou, and what you can do to avoid it.

Heat stress occurs when the body’stemperature rises beyond safe limits.Field workers may suffer heat stresswhen air temperature, humidity, radiantheat, and lack of air movementcombine with heavy work andprotective clothing to raise bodytemperature. Evaporation of sweat is


Figure 5.1—Heat stress . Unacclimated or unfit workers will suffer at lower levels of heat or work (chart is based on shaded air temperature, moderate radiant heat, light breeze, standard firefighter clothing, and moderate work rate).

the body’s main line of defense againstheat. As sweat evaporates, it cools thebody. When water lost by sweating isnot replaced, the body’s heat controlsbreak down and body temperatureclimbs dangerously. When the bodycan’t cope with this added heatburden, we experience heat stressdisorders including heat cramps, heatexhaustion, and heat stroke.

Heat stress can be measured in anumber of ways. Figure 5.1 provides asimple way to estimate thetemperature and humiditycombinations likely to cause problems.

Heat CrampsThese painful muscle cramps strikeworkers who sweat profusely in theheat. They seem less likely when fluidintake is adequate and the dietincludes bananas, oranges, freshsalads, and a sprinkling of table saltwith meals. Treatment involveselectrolyte drinks (tomato juice, sportdrinks, lightly salted water), andstretching to relieve the cramps.

A


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Heat ExhaustionThis disorder is characterized byweakness or extreme fatigue; unstablegait; wet, clammy skin; headache;nausea; and collapse. It is caused byinadequate fluid intake, salt losses, orboth. The fluid loss leads to a drop inblood volume that severely limits workcapacity. Salt loss reduces themuscles’ working capacity. Treatmentincludes rest in a cool place andelectrolyte drinks.

Dehydration ExhaustionThis form of heat exhaustion occursafter several days of work in the heat.If water losses are not replaced daily,progressive dehydration severelyreduces work capacity. Weight loss isthe best indicator of dehydration; aweight loss of 2% or more isaccompanied by diminished workcapacity. Exhaustion and collapse mayfollow weight loss exceeding 5%.Treatment includes fluid replacementand rest until water losses andelectrolytes are restored.

Heat StrokeHeat stroke is a medical emergency.Send for medical help at once andbegin treatment immediately. Braindamage and death may result iftreatment is delayed.

Heat stroke results from failure of thebody’s heat controlling mechanisms. Itis characterized by:

• Hot (often dry) skin

• High body temperature (106 oF orhigher)

• Mental confusion, incoherentspeech, delirium

• Loss of consciousness,convulsions, coma.

Rapidly cool the victim by soaking withcold water and ice, and by fanningvigorously to promote evaporativecooling. Continue until the victim’stemperature drops. Treat for shock if

necessary once the temperature haslowered. Transfer to a medical facilityas quickly as possible.

Preventing HeatStress

While the recognition and treatment ofheat disorders is important, the bestapproach to heat stress is prevention.Your actions in the months, weeks,and days preceding exposure are asimportant as the things you do whenyou are exposed to heat stress.

FitnessAchieving and maintaining a high levelof aerobic fitness is one of the bestways to protect yourself against heatstress.

• The fit worker has a well-developed circulatory capacity, aswell as increased blood volume,which is essential to regulatebody temperature in the heat.

• Fit people start to sweat at alower body temperature, so theywork with a lower bodytemperature and heart rate.

• Fit workers adjust or acclimatizeto work in the heat twice as fastas unfit workers (4 dayscompared to 8). They loseacclimatization more slowly andregain acclimatization faster thanunfit workers.

• Unfit, overweight workers areeven more unsuited for work inthe heat. They carry more weightand do not have a correspondingincrease in surface area forevaporative cooling.

The effect of the wildland firefighters’uniform on firefighters working in heatwas studied recently at in theUniversity of Montana HumanPerformance Laboratory. The fittestworker finished a 2-hour work test inthe heat chamber with a heart rate of

118 beats per minute, while the least fitlabored at a rate of 164 beats perminute. All subjects were working atthe same rate and grade on thetreadmill. There was a highlysignificant relationship betweenaerobic fitness and the working heartrate (r = -0.91). Differences in fitnessfar overshadowed variations in theuniform.

AcclimatizationThe worker who is acclimatized towork in the heat runs less risk of heatstress. The body adjusts to hot work in4 to 8 days by:

• Starting to sweat at a lower bodytemperature

• Increasing sweat production

• Decreasing skin and bodytemperature

• Improving blood distribution

• Decreasing heart rate.

About 11/2 hours of work a day is

enough to acclimatize workers to aspecific combination of work and heat.It provides partial acclimatization tomore severe conditions. Fitnesstraining activities also provide partialacclimatization. Adjust to hot weatheractivity gradually. Set a sensible pace,take frequent breaks, replace fluids,and don’t expect full production for thefirst several days.

Acclimatization persists for severalweeks, especially with regular physicaltraining. A tough weekend (fatigue,sleep loss, alcohol consumption) leadsto some loss of acclimatization.

On the JobYour best defense against heat stressis knowing when it is likely to strike.Temperature and humidity are yourbest clues;

• Is it hot—due to sun or nearbyflames?


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• Is the air still, with no breeze forcooling?

• Is sweat dripping off your body?

• Is your heart pounding at a rapidrate?

• Are you breathless, dizzy, chilled,nauseous?

If the answer to any of these questionsis yes, beware of heat stress. Continuehard work without taking precautionsand you will become a prime target fora heat disorder. Here are somespecific steps to take to prevent heatstress.

Replace FluidsDrink lots of fluids, before, during, andafter hot work. It is common to losemore than a liter of sweat an hour(about 1 quart or 1.5% of body weight)during work in the heat. In a hot, humidenvironment sweat rates can approach3 liters an hour for short periods.Maximum sweat loss in 8 hours is 8 to12 liters. Adequate replacement ofwater, salt, and potassium is vital tomaintain work capacity and to avoidheat disorders. For every liter of waterloss, core temperature increases morethan 0.5 oF, heart rate increases 8beats per minute, and the cardiacoutput declines, making work moredifficult. To prevent dehydration:

• Drink 1 or 2 cups of water or juicebefore work

• Take frequent drinks during eachhour of work (1 liter per hour)

• Drink as much as possible atlunch and the evening meal

• Continue replacing fluidsthroughout the evening

• Limit caffeine drinks (coffee, cola)that increase the loss of urinaryfluid

• Avoid alcoholic drinks that lead todehydration.

Thirst always underestimates fluidneeds, so start drinking before you getthirsty. It is not easy replacing 8 ormore liters of fluid a day, but it must be

done when performing hard work in theheat. Some think sport drinks are theanswer.

Carbohydrate/ElectrolyteBeverages

Commercially available sport orcarbohydrate/electrolyte drinks havebecome popular for fluid replacementduring endurance sports andrecreational activities. The beveragesprovide carbohydrate replacement(glucose, sucrose, glucose polymers)to sustain energy and blood glucoselevels, and electrolytes (sodium,potassium) to replace electrolytes lostin the sweat. Of course, water is themain ingredient in these drinks.

Water is crucial for workers in heatstress conditions, especially sinceenergy and electrolyte needs can bemet with snacks and regular meals.Blood glucose levels can bemaintained with between-meal snacks.And well-planned meals provide forelectrolyte needs. Salt in foods andample use of the salt shaker providefor sodium needs; and bananas, citrusfruits and juices, and other foodsensure potassium intake.

However, studies show that workersdrink more when lightly flavored drinksare available, thereby ensuringadequate fluid intake. Carbohydrate/electrolyte beverages can help workersmaintain energy and work outputduring long periods without food orsnacks. A review of the need for thesebeverages suggests they may beuseful when workers:

• Lose more than 8 liters of sweatdaily (1 liter = 1.0567 quart)

• Are not acclimatized to heat

• Are performing prolonged,continuous work (over 60minutes)

• Skip meals, have mealsinterrupted, or lose appetite

• Burn more than 1000 calories perday than they replace with foodand drink.

• Are ill with diarrhea.

Management options include:

• Distribute packets ofcarbohydrate/electrolyte drink mixfor use in special conditions

• Supply a portion (25 to 50%) offluid resupply with thesebeverages

• Provide access to thesebeverages at all meals.

Research does not identify onecommercially available product orclass of products as best suited forwork or firefighting needs. However,carbohydrate/electrolyte beveragesthat contain glucose polymers (clumpsof glucose) provide more energy perliter. Generally speaking, use lowercarbohydrate concentrations (2.5 to 5grams/liter) when fluid replacement iscritical (in extremely hot conditions),and use higher concentrations (5 to 10grams/liter) when energy is the primaryneed. Extremely high carbohydrateconcentrations have been shown toslow the entry of water into thecirculation during vigorous exertionsuch as running.

Studies show that urine production isreduced and fluid retention enhancedwhen fluid replacement beveragesinclude some electrolytes, ensuring abetter blood plasma volume for cardiacoutput, and more water fortemperature regulation by sweating.When sweat loss is high,carbohydrate/electrolyte beveragesensure greater fluid intake andretention, and provide an energysupplement. However, water continuesto be the primary form of fluidreplacement. Packets of powderedconcentrates provide the worker theopportunity to dilute the beverage topersonal taste, and to supplementcarbohydrate and electrolyte needs tomaintain work performance.

Replace ElectrolytesSodium lost in sweat is easily replacedduring meals, and with liberal use of


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IndividualDifferences

Individuals differ in their responseto heat. Some will always be atgreater risk for heat disorders.Reasons include inherited differ-ences in heat tolerance, such asperspiration rate, variations inbody composition, nutrition, hy-dration, or fatigue. Illness, drugs,and medications can also influ-ence your body’s response towork in a hot environment. If youare using medications, or havemedical conditions, ask your phy-sician or pharmacist if they posea threat. You should monitor yourresponse to heat and watch outfor signs of heat stress. Whenpossible, weigh yourself in themorning (after toilet but beforebreakfast) to watch for dehydra-tion. If your weight is down, rehy-drate before you return to work.Take your wake-up heart rate tosee if you are dehydrated, over-tired, or have a fever. A rate 10%above your average could indi-cate a problem. Finally, alwayswork or train with a buddy whocan provide help if you becomedisoriented or disabled with a heatdisorder.

the salt shaker. Unacclimatizedworkers lose more salt in the heat sothey should pay particular attention tosalt replacement at meals and duringwork (for instance with carbohydrate/electrolyte beverages).

But don’t overdo salt replacement. Donot use salt tablets. Too much saltimpairs temperature regulation, soheat disorders become more likely.Excessive salt can cause stomachdistress, muscle soreness, fatigue,impaired heart function, high bloodpressure, potassium loss, and mentalconfusion. Don’t continue a high saltintake when you return to less arduousworking conditions.

Potassium can become depleted overextended periods of work in the heat,so make potassium-rich foods likebananas and citrus fruits a regular partof your diet. Another approach is todrink lemonade or tomato juice andwater in quantities comparable to thefluid loss. Of course carbohydrate/electrolyte beverages also help tomake up for potassium losses.

RehydrationRehydration requires replacing bodyfluid. Drinking plain water is not aneffective way to rehydrate. Drinkinglarge volumes of water suppresses thedrive to drink and stimulates urineproduction. Rehydration fluids shouldcontain moderately high levels ofsodium and some potassium, or foodwith these electrolytes should beconsumed along with the fluids.Typical carbohydrate/electrolytebeverages do not contain enoughsodium for rehydration. To ensureadequate hydration, the volume of fluidconsumed should exceed the volumeof sweat lost.

Work HabitsPace yourself. Be aware that individ-uals may have large differences inheat tolerance. If you push too hard tokeep up with others, you may not lastthe whole work shift. When possible:

• Avoid working close to heatsources

• Do the hardest work during coolermorning or evening hours

• Change tools or tasks to minimizefatigue

• Take frequent short (30 second)rest breaks

Rest PeriodsWork/rest cycles must be adjusted toprevent progressive fatigue. Shorterwork periods and more frequent restperiods in a cool, shaded areaminimize heat buildup. Experienceshows that heat stress is unlikely whenyour heart rate is under 100 beats perminute after 3 minutes of rest.

Protective ClothingModern fire-resistant garments,designed to protect against sparks,embers, and brief exposure to directflame, do so at a price in terms of heatstress. Personal protective clothingstrikes a balance between protectionand worker comfort. The fabric thatprovides protection reduces airflowand evaporative cooling. Wear cottonT-shirts and underwear to help sweatevaporate. Wear loose-fitting garmentsto enhance air movement. And avoidextra layers of clothing that insulate,restrict air movement, and contribute toheat stress.

ColdBecause we generate heat during workand exercise, and because clothingcan be worn for protection, coldtemperatures do not pose a threatsimilar to that posed by hot, humidconditions. But exposure to lowtemperatures and high winds can leadto frostbite, hypothermia, and evendeath. The body cuts off blood flow tothe extremities during cold exposure,leading to discomfort and loss ofdexterity. Shivering is anothermechanism for maintaining bodytemperature, but large muscle physicalactivity is far more effective in restoringheat and blood flow. Because largemuscle activity takes considerableenergy, those exposed to cold weathermust maintain a reserve of energy foruse during prolonged effort and tomeet unforeseen emergencies.Excessive fatigue is the first step onthe road to hypothermia and possibledeath.

Wind ChillWind chill describes the effect of windspeed on heat loss (Figure 5.2). A 10 oFreading is equivalent to -25 oF whenthe wind speed is 20 miles per hour. Ifyou must face the wind on a cold day,be sure to cover exposed flesh and beon the lookout for frostbite.


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Figure 5.2—Wind Chill Index .

Actual thermometer reading ( oF)

50 40 30 20 10 0 -10 -20 -30 -40 -50 -60

Wind speed(mph) Equivalent temperature ( oF)

Calm 50 40 30 20 10 0 -10 -20 -30 -40 -50 -605 48 37 27 16 6 -5 -15 -26 -36 -47 -57 -68

10 40 28 16 4 -9 -21 -33 -46 -58 -70 -83 -9515 36 22 9 -5 -18 -36 -45 -58 -72 -85 -99 -11220 32 18 4 -10 -25 -39 -53 -67 -82 -96 -110 -12425 30 16 0 -15 -29 -44 -59 -74 -88 -104 -188 -13330 28 13 -2 -18 -33 -48 -63 -79 -94 -109 -125 -14035 27 11 -4 -20 -35 -49 -67 -82 -98 -113 -129 -14540 26 10 -6 -21 -37 -53 -69 -85 -100 -116 -132 -148

(Wind speeds Little danger Increasing Greatgreater than (for properly danger danger40 mph have clothed person)little additional Danger of freezing exposed flesh

effect)

Frostbite is damage to the skinresulting from cold exposure. Atemperature or wind chill of -20 oFseems necessary to produce frostbite.The skin appears pale and feels numb.Rewarm with warm (not hot) water, butdo not massage. Protect sensitiveareas (nose, ears, toes) to avoidfrostbite and the pain that occurs withrewarming.

Hypothermia begins when the bodyloses heat faster than it can beproduced. Fatigue and energydepletion compound the problem, asdoes rapid cooling from evaporation ofsweat, snow, or rain. When the coldreaches the brain, the body begins toshut down. This is a medicalemergency and the victim should betransported to a medical facility asquickly as possible. Hypothermia oftenoccurs at temperatures above 30 oF.

To avoid cold weather problems:

• Dress in layers, with wickinggarments and a weatherproofslicker

• Take layers off as you heat upand put them on as you cool off

• Wear a hat that protects your ears

• Maintain energy level and avoidexhaustion

• Acclimate to the cold to minimizediscomfort.

While cold air will not freeze thetissues of the lungs, even at subzerotemperatures, it may make vigorousexercise difficult for those prone toairway constriction. Slow down anduse a mask or scarf to minimize theeffect of cold air on airways.

Altitude

Field work and firefighting often takeplace at moderate altitude. Elevationsbelow 1500 meters (about 5000 feet)have little noticeable effect on healthyworkers. But as you ascend above1500 meters, available levels of

atmospheric oxygen decline. With lessoxygen available, altitude alwaysreduces work capacity. While highly fitworkers can do more at altitude, theytoo are affected by the diminishedoxygen supply.

Altitude AcclimatizationIt is possible to make a partialadjustment to the demands of altitude.Altitude affects our ability to take in,transport, and utilize oxygen. Work ataltitude leads to acclimatization by:

• Increased air intake (ventilation)

• Improved oxygen transport(increased red blood cells)

• Improved utilization of oxygen inmuscles (and increasedcapillaries).

These adjustments reduce—but nevereliminate—the effect of altitude onaerobic fitness. While it takes severalweeks to make a good adjustment to ahigher elevation, athletes have learnedthat they can improve with a week of


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Sickle-Cell TraitThis inherited abnormality,found mainly in blacks ofWest African descent affectsthe hemoglobin molecule ofthe red blood cells. The traitmay cause normally sphericalred blood cells to becomecurved or crescent-shapedwhen someone is at highaltitude, particularly if theyare dehydrated andexhausted. Workers with thesickle-cell trait can avoid acirculatory crisis bymaintaining hydration andavoiding fatigue whileworking at higher elevations.

Table 5.1—Permissible exposure limits for some health hazards of smoke .

Respirableparticulate Benzene CO Acrolein Formaldehyde

mg/m 3 ppm ppm ppm ppm

TWA 5 1 50 0.1 0.75

STEL — 5 — 0.3 2.0

Ceiling — — 200 — —

TWA = Time-weighted average.STEL = Short-term exposure limit.Ceiling = Level not to be exceeded.

altitude training for every 300 meters(1000 feet) above 1500 meterselevation.

If your crew works at an elevationabove 1500 meters, take it easy for thefirst few days, Take frequent breaksand avoid excessive fatigue. Planmore time to recover after hard work.Eat a high-carbohydrate diet for addedenergy. Take special care to maintainhydration since altitude hastens fluidloss. As with heat stress, individualsdiffer in altitude tolerance. Above 2400meters (about 8000 feet) a fewworkers may begin to experience mildsymptoms of acute mountain sickness(AMS), characterized by headache,fatigue, and lack of appetite. They willrequire more time to adjust, possiblyincluding recovery time at a lowerelevation.

Health Hazardsof Smoke

Concern for the health hazards ofsmoke from prescribed fires and fromwildfires is long-standing. The 1987–1988 fire seasons intensified interestand prompted comprehensive study ofthe problem.

Employee ExposureStudies of breathing zone air samplescollected on wildland firefighters andworkers involved with prescribedburning indicate some potential forhazardous exposure to respirableparticulate, carbon monoxide,formaldehyde, and acrolein. Exposuresseldom exceed permissible exposurelimits (PEL) or short term exposurelimits (STEL) mandated by OSHA (theOccupational Safety and HealthAdministration) (Table 5.1). Exposuresexceed OSHA standards less than 5%of the time on prescribed fire, and evenless on wildfires.

Respirable particulate iscomposed of particles of airborne sootsmall enough to find their way to thelungs. They irritate and burden airwaysand risk transporting carcinogens intothe lung.

Carbon monoxide is a colorless,odorless product of incompletecombustion that combines with

hemoglobin, reducing the oxygen-carrying capacity of blood.

Formaldehyde is a strong irritantand potential carcinogen found in thesmoke of forest fires.

Acrolein is a strong aldehyde thatstings and burns eyes and irritates theairways.

Vegetative smoke contains many moreproducts, including benzene, formicacid, and sulfur dioxide. Workers usinggasoline-powered tools, such as chainsaws or pumps, risk additional exposureto benzene. But the values seldomapproach permissible exposure limits.

Monitoring ExposureData from the Forest Service’s PacificNorthwest Research Station and theIntermountain Fire SciencesLaboratory agree that carbonmonoxide is highly correlated to othertoxins in smoke. Because of theserelationships, carbon monoxide can beused to monitor firefighter exposureand avoid excess exposure to theother hazards in smoke (respirableparticulate, formaldehyde, acrolein). Acarbon monoxide time-weightedaverage (TWA) of 25 ppm (parts permillion) ensures that exposure to othergases and particulate remains withinpermissible limits. This carbonmonoxide limit, which is below theOSHA permissible exposure limit of 50


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Figure 5.3—Effects of carbon monoxide concentration and exposure duration on blood carboxyhemoglobin (COHb) levels . The goal of monitoring its to keep % COHb below 5%.

20

10

200 ppm

100 ppm

50 ppm

% C

arb

oxy

hem

og

lob

in

Exposure Duration – Hours

5

1

5

8

ppm or the NIOSH (National Instituteof Occupational Safety and Health)standard of 35 ppm, also accounts foraltitude; long, strenuous work shifts;and the variability in particulate andformaldehyde levels (Figure 5.3).

Health EffectsExposure to smoke has the potential tocause short-term, intermediate, andlong-term problems.

Short-term exposure causes eyeirritation and coughing, and can causerespiratory effects. Studies of theeffect of smoke exposure onfirefighters have shown small butstatistically significant daily andseasonal declines in pulmonaryfunction. However, pre- to post-shiftchanges usually recover by thefollowing day, and pre- to post-seasonchanges recover after a period freefrom exposure. With adequaterecovery time the human lung isremarkably capable of cleansing itself.

Intermediate exposure (days orweeks) to the constituents of smokereduces the effectiveness of themucociliary escalator, which sweepsparticulate trapped in mucus upwardfor removal by expectoration orswallowing. When particulate is notremoved effectively, the risk ofbronchitis is increased. Prolongedcontinuous exposure may compromisethe effectiveness of the immunesystem.

Long-term exposure risks from yearsof firefighting have not beenestablished. The constituents in smokehave the potential to increase the riskof heart disease, chronic lung disease,and cancer, but there is no evidencethat the intermittent exposure offirefighters to low levels of smoke fromforest fires has increased these risks.Confounding factors for long-termstudies include cigarette smoking,secondhand smoke, residential woodburning, air pollution, radon, and otherrespiratory exposures.

Firefighting andthe ImmuneSystem

While the smoke from forest fires is notconsidered immediately dangerous tolife and health, there is no question that itcauses unpleasant symptoms (phlegm,coughing, wheezing, sore throat, burningeyes), and sometimes leads torespiratory illness. A number of factors inthe firefighting environment influenceimmune function and the body’s suscep-tibility to respiratory and other illnesses.

SmokeChronic exposure to the smoke fromcigarettes reduces immune function,influences the response to other agents,such as carcinogens, and increases therisk of heart disease, lung cancer,chronic respiratory problems, and otherailments. Prolonged exposure to thesmoke from wildfires has the potential tocause some of these effects. However,firefighting is seasonal, exposure isepisodic, exposures seldom exceedallowable limits, and the healthimplications of these exposures have notbeen determined.

StressStress is a neuroendocrine response toevents that are perceived to bephysically or psychologically threatening.The body’s endocrine system respondsby producing hormones that arenecessary for the fight or flight response.However, prolonged exposure to thesehormones can lead to immunesuppression and increased susceptibilityto infection and illness.

FatigueProlonged exertion and exhaustion leadto suppression of the immune system,slow healing of wounds, and vulnerabilityto upper respiratory infections, as well aspoor performance, muscle soreness,irritability, sleep disturbances, andpsychological problems, such asdepression.


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NutritionJust as certain nutrients (Vitamins C,E, Beta-carotene) help to maintain ahealthy immune system, poor nutritioncan weaken it. See the section onnutrition for more on this subject.

While smoke is one threat to theimmune system, stress, fatigue, andpoor nutrition also lead to poor immunefunction and increased risk of upperrespiratory and other problems. Tomaintain a healthy immune system andminimize the risk of respiratory illness,

avoid prolonged exposure to smoke;manage stress through communicationand training; improve fitness and userest and labor-saving tools to minimizefatigue; and eat a variety ofvegetables, fruits, and other immunefriendly foods.

chapter 5 environment and performance - us forest … 5— environment and performance 34 heat...

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