How do you test whether PPE creates employee susceptibility to heat stress? Get a Sweating Thermal Manikin (STM).
The National Personal Protective Technology Laboratory (NPPTL) at the National Institute for Occupational Safety and Health (NIOSH) has added a manikin to its stable of PPE testing programs.
The STM measures heat transfer through various fabric combinations worn by firefighters, miners and healthcare workers.
NPPTL’s objective: to help create less burdensome materials for protective clothing used by workers who face the risk of heat stress.
The lab calculates a Total Heat Loss number: an indicator of how much heat a garment’s fabric will trap.
While that’s been helpful to create better PPE materials over the years, experts say it’s also been necessary to test two other variables:
- how various features such as pockets, padded knees or elbows, and zippers affect heat retention, and
- ensembles — several pieces of protective clothing used together.
To test those two variables, NPPTL traditionally used volunteer human subjects. But human sweating, of course, varies from person to person.
That’s where the manikin comes in.
“If we want to compare one specific ensemble to another, we don’t want to use human beings, because of individual variations,” according to Dr. Jon Williams, a researcher at NIOSH. “So if we want to look at a standardized response, we test all of the different kinds of ensemble types on a sweating thermal manikin.”
In testing, the manikin is set to sweat once a certain skin temperature is reached. The sweat rate can be controlled by the researcher. A collection of pores over the exterior of the manikin is spaced to uniformly deliver water to the skin surface.
A YouTube video shows the manikin in action. Researchers put various PPE on it, including a respirator and gloves. A thermal projection on a computer screen shows various “hot spots” after the manikin has been “walking” for a while.