Walnut grove in Winters, California

Study Description

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The Field Study

Where we collect data:

We are visiting farms from the Imperial Valley through the San Joaquin and Sacramento Valleys to gather data and hold focus groups with field workers to get an in-depth understanding of  the laborer’s view of HRI, their perception of risk and what motivates or provides barriers to them to keep themselves hydrated and comfortable in the conditions of high heat.

CHIPS research team posing for photo in field with temperature data collection deviceIn the field:

To understand the effect of the different combinations of tasks, work-rates, weather and crop type we monitor the internal temperature of the field workers throughout the day. This is done by use of an internal temperature probe, which has been used safely for many years in athletes and firefighters.

To measure work rate we use two methods, heart rate (HR) - a HR monitor strap around the chest, and an accelerometer which measures movement and the intensity of physical activity, attached to the belt of the worker.  From the accelerometer we can get metabolic equivalent units (METs) One MET is your metabolic rate at rest, sitting quietly or lying down. [A vigorous workout, will increase your metabolic rate to 10 or 11 METs]. Combining the two gives us the best possible information about work rate and the contribution of physical work to overall body temperature.

We also measure how well hydrated the workers are at the start and end of their work day using body weight and a few drops of blood to see how concentrated (or dehydrated) they are. The workers also estimate what, how much and how frequently they drink on the day they are monitored.

A graduate student measured the effects of heat exposure and dehydration on kidney function. A urine sample was collected from male volunteers to assess kidney health. This was the first study to assess whether heat exposure puts California field workers at risk of kidney injury or chronic kidney disease. A paper has been published: Heat Exposure, Volume Depletion and Kidney Function in California Agricultural Workers.

Another factor is the choice of clothing. From our first field study in the summer of 2012 we have observed different styles of dress – from loose, light clothing to many layers and thicker materials.  Although it appears that wearing several layers of clothing would be counterproductive while working in the heat, there are also theories that more layers of clothing, some of which may not be loose, will allow sweat to evaporate over a wider body area and over a longer period of time. There is no norm in place of what type of clothing to wear in various environmental conditions and work levels in agricultural work. We will catalogue clothing and use an Infra-Red camera to determine both skin temperature and sweat evaporation from workers. Defining the appropriate clothing and layers adapted to CA summer conditions will be an innovation and major contribution to the health and safety of farmworkers laboring in excessive heat.

To measure the heat inputs from the environment, the workers wear heat ‘pens’ which are pen-sized data loggers recording ambient temperature and relative humidity throughout their work shift. None of this equipment interferes with their ability to work normally.

Each worker that volunteers for the study will be monitored for just one day. They receive compensation for the extra time and effort they give to the research, and the study has an active protocol approved by our Human Subjects Protection Committees to protect the rights of our participants.