Farmworkers weeding crops in field

Pilot Results

Specific Aim 1

Versiòn en Español

To increase the understanding of physiological responses to environmental heat and varying physical work in agricultural laborers.  From the data gathered, we will develop hypotheses and propose strategies to reduce the risk of HRI.

Preliminary Results from the 2012 pilot study.
7 different farm locations were visited in the California Central Valley and 100 workers assessed.



Workers drank on average almost 95 fluid ounces (men) and 57 fluid ounces (women) at work, of which most was water. All were allowed to drink as much as they wanted while at work; water was ready available.  However 22% of the 100 workers lost over 1.5% of their original body weight. The American Conference of Industrial Hygienists (ACGIH)  indicate workers are at increased risk of dehydration if they lose more than 1.5% of body weight in a work shift. 80% exhibited increased serum osmolality, a measure of concentration of the blood, with 21% experiencing at least a 3% increase in blood 'thickness'

Line graphs showing heart rate and smoothed heartrate as well core temperature


Along with many experiencing mild hydration, the 'heat pill' indicated that the baseline core body temperature was on average 37.1 0C, while the baseline heart rate was on average 75 beats per minute.  Eight workers had a core temperature elevated above 38.50C  but none above 400C . A measure of risk of heat illness, the PSI or Physiological Strain Index which includes measures of core body temperature raised above baseline and heart rate,(see below for formula), is considered significant if the PSI ≥ 7.5.  Only 5% (4 out of 86 with both core temperature and heart rate profiles) of the group were classed as 'at risk' on this scale.

PSI = 5(peak core temperature – base core temperature)/ (39.5 – base core temperature) + 5(peak heart rate – base heart rate)/ (180 – Base hear rate).

Line graph showing weather conditions on the same day

Specific Aim 2

To interview a wide variety of field workers in focus groups, and employers using a structured questionnaire; so obtain information about social and cultural expectations that may prevent field workers protecting themselves when at risk for HRI. We will use focus groups and key interviews to evaluate the feasibility and acceptability of solutions suggested by the information developed from Specific Aim 1.

The California Institute for Rural Studies (CIRS)  conducted five focus groups and 15 key informant interviews in the summer of 2013. Three focus groups were in Spanish and two in Mixteco, and one group was entirely female, three others only had male participants. The information is still being abstracted, but general trends indicate that education or advice concerning protection against heat related illness is preferred orally rather than in writing, or even picture formats. The frequency of drinking water while at work varied enormously, as well as the actual quantity of water or other beverage.
Workers in general preferred to be paid by the piece rate system as it both gave them an opportunity to be paid more, and gave them more control over their work rate and work day. None participating in the focus groups felt intimidated or unable to stop work if they were feeling ill.


Farmworkers carry red buckets full of green chili peppers on their shoulders through the field