Bodytrak’s Physiological Strain Index (PSI) Algorithm – An Innovative New Solution For Predicting The Onset Of Occupational Heat Stress

Occupational heat stress occurs when a worker begins to lose the ability to control their internal body temperature, through over-exertion in excessively hot industrial environments or from being exposed in hot weather over too long a period. This risk can also be a factor for individuals wearing heavy Personal Protective Equipment (PPE) and clothing which can hamper the body’s ability to thermoregulate.

Historically, thermal comfort and heat stress have been estimated using measures such as WBGT (Wet Bulb Globe Temperature), and Standard Effective Temperature (SET). WBGT uses humidity, air temperature and infrared radiation (directly from the sun) whereas SET takes into account additional factors such as air speed, metabolic heat generation, heavy clothing and the level of skin sweat. Whilst these measures can provide reasonable predictions for the likelihood of a group of individuals experiencing heat stress, they are largely dependent on environmental measurements and do not take into account the physiological differences between each individual.

Drawbacks of these methods include a tendency to overestimate measurements when in direct sunlight and also not taking into account the level of PPE being worn, as these variables will affect people in different ways. For precision monitoring and reliable protection from heat stress, measures for thermal comfort should be based on true physiological readings obtained for the specific individuals who may be at risk.

There is an increasing need for more relevant human performance and health status indicators to help protect individuals when working in climatically hot or high temperature industrial environments. The Physiological Strain Index (PSI) is a medically recognised measure where a value of between 0 and 10 is used to indicate the risk of heat stress to individuals. A PSI scale uses simultaneous readings of heart rate and core body temperature to provide a highly reliable indicator of a person’s ‘physiological strain’ and thus an indication of whether heat stress will occur. In this sense it can be used as a straightforward and immediate indicator of the level of risk. This risk is minimal when the PSI shows a low value and will obviously increase if this value begins to rise. If the value is indicated above a certain threshold then the risk is seen as imminent.

A key challenge facing the industry sectors seeking to improve their workers’ protection, stems from the complexity of measuring core body temperature of a worker in real time and on the move. The most common and reliable means of measuring core body temperature uses a standard hand-held tympanic (in-ear) thermometer or swallowing a gastrointestinal (GI) tract temperature pill for continuous measurement as the pill passes through, and exits, the individual’s body. Clearly, obtaining both a continuous and reliable measurement using these methods has its challenges for a non-stationary person, especially in industrial environments, and both have additional issues regarding practicality and cost at scale.

Bodytrak’s Cloud-based PSI Algorithm

Bodytrak’s approach has been to develop an algorithm based on PSI using accurate heart rate and core body temperature measurement as a basis for continuous, reliable monitoring for heat stress. The Bodytrak earpiece is uniquely able to simultaneously measure both tympanic temperature and heart rate values for PSI due to its non-invasive design and highly accurate embedded biometric sensors. The solution provides both the individual and a remote monitor with a clear graphical interface which displays the PSI value in real time. The PSI algorithm is derived using a combination of data processing from both the device’s onboard embedded system and the Bodytrak Cloud’s processing capability. The Bodytrak PSI feature also translates into a real time alert when it detects an individual is at high risk. This alert is both in the form of an automatic in-ear audio communication, and an emergency alert to a remote monitoring station which will have real time access to a display showing a “vitals dashboard” for each person wearing the Bodytrak earpiece.

The PSI algorithm is part of a suite of industry leading proprietary algorithms, specifically developed by Bodytrak using IoT technology to deliver connected advanced solutions to protect workers in hazardous environments. For situations where heat stress and heat related illness are a real danger for workers and where real time monitoring is needed to minimise and manage this risk, Bodytrak’s innovative solution provides workers with the highest levels of protection.