Understanding Physiological Strain in Industrial Environments

Understanding Physiological Strain in Industrial Environments

In our two part blog, Keeping Your Finger On The Pulse Of Your Team we took a look at heart rate and why it is an important measure when considering the physiological strain of your team. While heart rate is something we are all familiar with, physiological strain index (PSI) may be a metric many of us are less aware of and how it can be used when reviewing our health and preventing workplace incidents.

Here we take a deep dive into understanding PSI and how it is relevant to workplace health and safety.

What is the physiological strain index?

What insights can monitoring PSI provide?

How can monitoring PSI help when inducting new employees? 

How can monitoring PSI help with existing employees? 


What is the physiological strain index?

Developed by a number of researchers in the late 1990s, PSI is a simple and effective measure of heat strain that relies on heart rate and core body temperature (CBT) data of an individual. The calculation compares the individual’s heart rate and CBT at any given time with their normal values when they are resting. The results help determine how their body is responding to the physical stress from the workload and if the person is experiencing any signs of heat stress. 

PSI operates on a universal scale of 0 to 10 to help classify individuals into relevant risk categories. On the scale 0 indicates no physiological strain while 10 represents the highest physiological strain, indicating extremely strenuous conditions.

Previously PSI may have been challenging to calculate in real-world work environments and industrial settings as the measurement is only as effective as the quality of the heart rate and CBT data inputs. ECG devices provide the most accurate readings for heart rate, however, these are cumbersome and not portable. When measuring CBT, rectal probes are known to be an accurate and cost effective measure to capture an individual’s CBT, however, this is an extremely invasive method and not at all practical in the workplace. The gastro-intestinal pill is the gold standard measure for CBT, but this is very costly at scale and can be affected by food and fluid consumption so is not a suitable option. With the evolution of wearable technology, measuring PSI accurately is much more accessible. Solutions like Bodytrak are able to provide a non-invasive and cost-effective scalable solution. Due to the position of the Bodytrak in-ear device it is possible to obtain accurate heart rate and CBT readings to ensure the reliability of the overall PSI value. Validation of Heart rate data from Bodytrak shows a mean absolute error of 2.87% compared to a control ECG device (industry standard acceptable error rate is considered to be 5%), and CBT data from Bodytrak shows a mean absolute error of 0.18°C compared to a gastro-intestinal pill. This is a strong indication of the effectiveness of the solution to provide a viable PSI.


What insights can monitoring PSI provide?

As global temperatures continue to rise, there’s an increasing number of employees across various sectors who are being exposed to higher temperatures. In such environments, the body is not only working to complete the tasks they’re responsible for – such as heavy lifting and other high levels of physical activity – but it is also working on thermoregulating to ensure it remains cool.

Monitoring PSI continuously will highlight the strain any individual is under. An individual reaching a higher PSI can indicate that the employee should remove themselves from the environment. This could be moving to a cooler environment, drinking water to increase hydration or rest to allow the body to recover in order to return to a safe level. When the index reaches 10 this is vital as they are at a high risk of a heat-related illness as they are not able to adequately control their core body temperature.


How can monitoring PSI help when inducting new employees? 

The physiological responses to different workplace stressors, such as environmental temperatures, will differ for each individual, depending on numerous factors including age, activity level, personal protective equipment (PPE) worn, ambient conditions, and acclimatization level. Industry figures show 50% to 70% of fatalities often occur in the first few days of exposure to hot environments as the body needs time to build a tolerance to the new environment gradually. 

A lack of acclimatization represents a major risk, especially for new recruits. If you consider a new employee who has just started working in a hot environment, such as an aluminum smelter or a courier who is making deliveries in the height of summer, their heart rate would increase due to workload but also so that that more blood flow and heat is transferred to the skin for thermoregulation. If this employee is wearing a smartwatch or other consumer wearable they will likely see their heart rate increasing. More advanced monitoring solutions like Bodytrak takes into account core body temperature as well as heart rate to provide a more accurate picture and predict how the body may respond over time. The rate at which heart rate alone can fluctuate is not enough of an indicator in industrial occupational settings when you want to prevent incidents before they happen.  As the new recruit acclimates, their PSI score will become lower and it will take a longer time or more physical exertion to raise the score. 

The ability to understand how long it may take for an individual to acclimate or recover and respond to stressors can provide extremely useful data for organizations when developing and improving their induction and training programmes. 


How can monitoring PSI help with existing employees? 

For existing employees monitoring PSI can be a strong indicator during recovery periods and help determine when it is safe for a person to return to the environment or continue with their tasks. Regardless of the individual it will continue to reveal the general strain an employee is under and can act as a reminder when they may need to remove themselves from an environment in order to recover. Bodytrak is an individualized machine learning solution that accounts for each person’s individual physiological response, rather than a one-size-fits-all indirect measurement approach (i.e. ambient environment monitoring).

There is an increasing need for reliable methods to prevent incidents in the workplace. Ensuring physical workloads are maintained at the right levels to ensure success and over exertion is avoided is effective for the organization to ensure retention and reduce absenteeism. The physiological strain index was developed as a measure to identify heat strain. While it is an effective indicator, it is not well known as historically it has not been possible to measure it in industrial environments. Bodytrak has developed an accurate and non-invasive solution to capture PSI so that it can be implemented to prevent heat illness and associated injury costs. Learn more about monitoring PSI by speaking to the team today.

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