Table 2 Key data, findings and critical appraisal scores (CAS) and methodological quality ratings of included articles

Cuddy et al. [1]

15 Hot Spot firefighters

(12 male, 3 female)

Wore PPE

Water turnover

Nude BW

Live wildland fire suppression over 3 days of work shifts (11.4 ± 0.7 h/day) (hiking, line dragging, laying hose, chain sawing, clearing brush, lookout, and scouting)

Ad libitum drinking

27.5 ± 3.2 °C mean ambient temperature

No significant change (p = 0.12) in morning BW across 3 days (pre 77.3 ± 8.3 kg, post 77.0 ± 8.9 kg)

Mean water turnover 9.5 ± 1.7 L/d

54

(Fair)

Raines et al. [2]

32 firefighters (31 male,1 female)

Ad libitum(AD) group (n = 17), pre-shift (PR) group (n = 15)

PPE

Plasma Osm

Urine colour

USG

PR group consumed 500 mL fluid bolus pre shift and ad libitum remainder of shift

7 days (9.9 ± 2.2 h/day AD, 9.7 ± 2.3 h/day PR) of wildfire suppression (intense but intermittent work, using chainsaws, applying water, carrying, transit time and briefings)

Mild to warm ambient temperatures (15.8–26.4 °C)

No difference between groups in total fluid intake (3.4 ± 1.6 L AD, 3.7 ± 2.9 L PR, p = 0.730)

No significant differences between groups for any hydration marker (urine colour, p = 0.44; USG, p = 0.92; plasma Osm, p = 0.41)

Significant decrease in both urine colour (p = 0.001) and USG (p = 0.01) across the shift, but still dehydrated by end, though less than at start

Plasma Osm indicates firefighters arrived on shift dehydrated and finish dehydrated (p < 0.0001)

57

(Fair)

Horn et al. [6]

35 career, volunteer and industrial firefighters (31 male, 4 female)

Wore PPE and SCBA

Nude BW

Urine colour

USG

Urine Osm

Salivary Osm

3 h live fire training exercise in specialised training building. 3–4 evolutions lasting 15–25 min, separated by 10–15 min (obtain water, advance hoses, extinguish fires, forcible entries, search and rescue and ventilation tasks)

Encouraged ad libitum drinking (water and sport drink)

Cool autumn day

Significant BW loss of 1.1 ± 0.8 kg (p < 0.001) and 1.9 ± 0.9 kg (2.2 % BW loss) adjusted for fluid intake and voiding

Significant (p < 0.001) increase in salivary Osm (pre 78.0 ± 21.5 mOsm/kg, post 49.0 ± 15 mOsm/kg), reflective of dehydration

No significant (p > 0.05) changes in Urine Osm (pre 768 ± 260 mOsm/kg, post 712 ± 251 mOsm/kg), urine colour (pre score 5.8 ± 1.5, post score 5.3 ± 1.5), or USG (pre 1.025 ± 0.009, post 1.024 ± 0.009)

61

(Good)

Holsworth et al. [7]

9 volunteer firefighters

(8 males, 1 female)

WorePPE and SCBA

HCT

2 × 30 min strenuous live structural fires

No fluid intake

Significant (p = 0.0014) change in HCT (pre 43.7 ± 3.1 %, post 46.1 ± 2.3 %), indicating significant dehydration

61

(Good)

Smith et al. [8]

11 male professional firefighters

WorePPE and SCBA (20.4 kg)

HCT

3 trials of 5 standardised firefighting drills in a training structure (carrying a hose up 4 flights, hoisting a hose, discharging a pump can, dragging a dummy, chopping a block of wood). 10 min rest between trials

No fluid intake

Unknown ambient temperature

Significant (p < 0.001) change in HCT (pre 43.2 ± 0.75 %, post 47.3 ± 0.75 %), indicating significant dehydration

57

(Fair)

Angerer et al. [9]

49 firefighter trainees

(all male)

Wore PPE and SCBA (24 kg)

Nude BW

30 min fire operation in a large simulation plant (ascending stairs, dragging hoses, fire suppression, dragging 80 kg dummy up and downstairs, crouched progression)

No fluid intake

Maximum 200 °C at 1.5 m above ground and 700 °C below the ceiling

BW significantly (p <0.001) reduced by mean 0.6 ± 0.2 kg

61

(Good)

Raines et al. [12]

34 firefighters (32 male, 2 female)

AD group (n = 17)

PR group (n = 17)

Wore PPE

Plasma Osm

Urine colour

USG

PR group consumed 600mLwater and 600 mL sport drink per hour of shift

One day (9.9 ± 2.2 h/day AD, 10.5 ± 2.2 h/day PR) of wildfire suppression (intense but intermittent work, using chainsaws, applying water, carrying, transit time and briefings)

Mild to warm ambient temperature (15.8–26.4 °C)

PR group significantly higher total water intake (7.1 ± 3.1 L PR, 3.4 ± 1.6 L AD, p < 0.001)

Both groups began work dehydrated according to USG (1.019 ± 0.007 AD, 1.016 ± 0.005 PR)

PR post shift had significantly (p = 0.001) lower USG (1.004 ± 0.002) than AD (1.016 ± 0.008)

Change from dehydrated to euhydrated for PR group only

Significant (p < 0.01) change in urine colour for both groups (pre score 2.8 ± 0.4 AD, 2.6 ± 0.5 PR,

post score 2.3 ± 0.8 AD, 1.4 ± 0.5 PR), but still dehydrated

Plasma Osm no different between groups (p = 0.371), both arrived dehydrated and post shift both significantly reduced (p < 0.0001) to achieve similar euhydration

57

(Fair)

Ruby et al. [15]

14 wildland firefighters

Wore PPE

Water turnover

USG

Urine Osm

5 day period of arduous fire suppression (hiking with load and fire line construction)

Ad libitum drinking

Unspecified ambient temperature

Water turnover 6.7 ± 4 L/day

No significant change in USG (pre 1.016 ± 0.006, post 1.108 ± 0.006)

No significant change in urine Osm (pre 562 ± 175 mOsm/L, post 629 ± 216 mOsm/L)

50

(Fair)

Raines et al. [18]

12 male wildfire firefighters

Wore PPE

Plasma Osm

2 days of 12 h live fire prescribed operation (controlled fire application, building containment lines with hoe, chasing spot fires and applying water)

Ad libitum drinking

Hot ambient temperature (30.9 ± 3.6 °C day 1, 32.8 ± 5.7 °C day 2)

No significant (p = 0.73) change in plasma osmolality (day 1 292 ± 1 mOsm/L, day 2 289 ± 0.5 mOsm/L), indicating euhydration throughout

57

(Fair)

Eglin et al. [28]

14 firefighter instructors

(all male)

Wore PPE and SCBA (20.2 kg)

USG

Nude BW (adjusted)

Fluid deficit

30 hot fire (HF) exercises (33 ± 7.9 min, 74 ± 42 °C)

6 fire behaviour (FB) exercises (26.3 ± 5.5 min, 45 ± 12 °C) and

8 fire attack (FA) exercises (7.3 ± 2.6 min, 139 ± 48 °C) performed on same day with 2 h rest in-between

Ad libitum drinking

Mean BW change 0.96 ± 0.41 kg/h, fluid deficit 0.62 ± 0.61 L HF exercises (0.79 ± 0.80 %/h)

Mean BW change 1.59 ± 0.57 kg for FB and FA exercises

Mild hypohydration at end of exercises with insufficient fluid intake to counteract body weight loss from sweating

No significant (p > 0.05) change in USG (pre 1.019 ± 0.08, post 1.021 ± 0.009)

50

(Fair)