CHAPTER 2: LITERATURE REVIEW
2.5 PREVALENCE OF DEHYDRATION IN FORESTRY WORKERS
There are a few international studies which have investigated the occurrence of dehydration in forestry workers. In SA, however, there have been no studies where the primary aim was to determine the prevalence of dehydration in forestry workers. The only information which suggested that SA forestry workers might be experiencing significant dehydration was published by Scott et al (2004). Scott et al (2004) were commissioned by the forestry industry to conduct an ergonomics investigation into the task demands of forestry workers in the humid coastal forests of Kwambonambi. As part of this investigation they inadvertently found that the chainsaw operators (n=39) and stackers (n=46) were dehydrated 2.9% and 3.7%25
25 When using percent loss of body weight as the measure of dehydration it is acceptable to refer to the loss as a dehydration of “x” percent. For example a worker who lost 3% of their body weight can be referred to as having dehydrated 3%.
respectively (Table 1). This study highlighted to the SA forestry industry that dehydration was a potential hazard that merited further investigation. The industry then commissioned this current study to explore the prevalence more comprehensively in an attempt to determine the prevalence, severity and implications.
Table 1:
Study
Summary of forestry studies reporting dehydration
Number Gender Job category
Mean % loss of body weight end shift
Scott et al (2004) 39 Males Chainsaw
operators 2.9%
46 Males Stackers 3.7%
Wigaeus et al (1985) Unknown Males, females Silviculture 3.2%
Trites et al (1993) 13 Males Silviculture 3.1%
3 Females Silviculture 3.1%
Paterson (1997) 8 Males Fellers 1.2%26
% with USG readings
>1.020g/ml end shift
Parker et al (2001) 30 Males Loggers 63%
Parker et al (2002) 24 Males Loggers “majority of the loggers”27 Similar findings were reported by studies done in other countries. In Vietnam, forestry workers (mainly women) who were involved in either harvesting or silviculture28 lost 3.2% of their body weight29 per working day as they neither ate nor drank during their shifts (Wästerlund, Chaseling
& Burström 2004 citing Wigaeus Hjelm & Frisk 1985) (Table 1).30
26The mean % loss of body weight at the end of the shift is less because these workers ate and drank during the shift unlike the workers in the other studies.
27The actual number or percent was not mentioned in the report.
28Silviculture is the planting of forests as opposed to harvesting the planted forests.
29A percent loss of body weight as little as 1 to 2% has been shown to impact negatively on both physical and mental performance (Maughan et al 2004, Gopinathan et al 1988) and according to the American College of Sports Medicine (ACSM) Roundtable on Hydration and Physical Activity Consensus Statements, a body weight loss of greater than 2% can negatively affect exercise performance (Casa et al 2005).
30Unfortunately this reference (Physical strain on Vietnamese forest workers) was unattainable as it was published in the Undersokningsrapport 1985: 5. Arbetarskyddsstyr-elsen, Forskningsavdelningen, Solna which was not available in SA.
Trites, Robinson & Banister (1993) reported a loss of body weight of 3.1% across the day in male (n=13) and female (n=3) workers involved in silviculture in British Columbia, Canada (Table 1). In both of these studies the findings regarding dehydration were incidental to the primary purposes of the investigation.
The only studies whose primary aim was to investigate the prevalence of dehydration in forestry workers were conducted in New Zealand (NZ). Paterson (1997) studied 8 fellers31 (mean age 27.8 years) who were working in standard protective clothing32
Parker, Ashby & Bates (2001) conducted a preliminary observational study in NZ to investigate the occurrence of dehydration (as measured by USG) in 30 loggers
at ambient air temperatures of 10.3°C to 21.9°C. These temperatures were similar to those expected in winter in SA. Paterson (1997) found that they voluntarily consumed an average of 2.7 litres (SD±1.2) of fluid per 7 hour shift but still dehydrated 1.2% (Table 1). No mention was made of the type of fluid consumed.
33 (mean age 34 years) wearing standard protective clothing who were working in moderate weather conditions.
Although this NZ study was done in autumn the mean ambient air temperature was 19°C which in many areas of SA is more representative of winter. These conditions posed a moderate threat for heat illness as calculated by the Wet Bulb Globe Temperature (WBGT)34 (Binkley et al 2002). Urine specific gravity was measured once at the end of a 5 hour shift. Parker et al (2001) concluded that 37% (n=11) were normally hydrated (USG≤1.020 g/ml), 60% (n=18) were dehydrated (USG>1.020 g/ml to ≤ 1.030 g/ml) and 3% (n=1) were seriously dehydrated (USG>1.030 g/ml) (Figure 5, Table 1).35
31 The nearest equivalent to fellers is chainsaw operators.
32Their protective clothing is similar to that worn locally and includes a helmet, ear muffs, high visibility shirt or vest, chainsaw resistant leggings and reinforced steel tipped rubber boots.
33 Loggers referred to anyone involved in harvesting (Parker 2007).
34The Wet Bulb Globe Temperature (WBGT) is an index calculated as WBGT = 0.7natural wet bulb temp
+ 0.3 globe temperature which is commonly used as an indication of the environmental conditions (Spioch & Nowara 1980).
35There is some confusion in the literature about the interpretation of the USG results. This study has used the guidelines of the ACSM which states that a USG≤1.020 g/ml indicates a euhydrated state and USG>1.020 indicates a dehydrated state (Sawka et al 2007, Sakwa’s comments in the Panel Discussion printed in the paper by Armstrong 2005). The category of serious dehydration (USG>0.030 g/ml) was taken from Casa et al (2000) to try and determine to some degree the extent of dehydration.
Their state of hydration on arrival at work was not
monitored. Most loggers drank 1 litre over a 5 hour shift. The fluids included water and/or tea, coffee and cola. This was substantially less than that found in the study by Paterson (1997).
Figure 5:
Parker, Ashby & Bates (2002) conducted a follow up study in NZ to determine the effect of seasonal changes on dehydration in 24 loggers (mean age 35 years) wearing standard protective clothing. USG was measured pre shift, pre break and end shift over a period of 4 consecutive days in both winter (mean ambient air temperature 10.9°C) and summer (mean ambient air temperature 18.5°C). According to the WBGT, the risk for heat stress in both seasons was low (Binkley et al 2002 Position Statement). Parker et al (2002) reported that the mean USG (1.025 g/ml) was not significantly different between the seasons and that most were dehydrated, some seriously so (Figure 6). A number arrived at work dehydrated (USG 1.025 g/ml) – the article was not clear as to what proportion this was. They found that the mean hydration had improved The end shift urine specific gravity measurement of 30 loggers (after Parker et al 2001)
by the break (USG 1.022 g/ml) and regressed again by the end of shift (USG 1.025 g/ml) (Table 1). Parker et al (2002) attributed the similar prevalence of dehydration between seasons to the fact that the loggers drank less in winter (1130 ml/shift) than in summer (1640 ml) as they perceived that dehydration was only a threat in the hotter weather. The loggers also wore more clothing to keep warm in winter, restricting the loss of heat (Ashby & Parker 2003).
Figure 6: The effects of season on dehydration in New Zealand loggers (after Parker et al 2002)
The prevalence of dehydration in forestry workers has been confirmed by a number of studies in different countries. Dehydration, with or without hyperthermia, has serious health implications for these workers.