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Identifying and Preventing a Cause of Operator Fatigue/Drowsiness

Updated: Mar 15, 2023

I have been on a world learning tour since February of 2023, meeting with industrial hygienists who are tirelessly working to protect miners from occupational hazards. During my travels, I came across a program that caught my attention - one that used technologies to detect operator drowsiness. However, as I delved deeper into this program, I began to realize that while the camera technology could detect closing/shut eyes, it could not prevent or identify the cause of the operator drowsiness.

There are several obvious reasons for operator drowsiness, including lack of sleep, poor diet, caffeine intake, alcohol use, illness, or medications. However, the most surprising discovery made, was that even fully-rested, healthy, non-medicated operators could suffer from drowsiness caused by the CO2 they produce while operating their machines.[NASA-STD-3001 Technical Brief Carbon Dioxide (CO2)] It wasn't until recently that CO2 was recognized as a cause of operator fatigue.

During my travels, I consulted on three accidents involving operators falling asleep at the wheel. One accident involved an articulated haul truck, another a 30-passenger bus, and the last, an ultra class haul truck. We were able to test the articulated haul truck after the accident. We collected data using the ISEEE 1002 In-field-testing- method, which uses direct measurement devices (CO2, temperature, humidity, pressure) that stream data to the cloud in real-time, providing continuous data on cab parameters while the machine is in operation.

The CO2 (black line) showed no sign of stabilizing during the 27 minutes of the test, starting at 1100 PPM and rising to 3800 PPM . The last verticle grey line indicates the test instruments were taken from the cab.

The graph displays the CO2 level as a black line that rose during the duration of the test. It was apparent that the CO2 levels were high enough for the operator to experience a micro-sleep, which is what the operator said was the cause of the accident. The test shows high CO2 levels after just ten minutes of operation. The operator worked a twelve-hour shift in the cab.

Identifying and preventing a root cause of operator fatigue/drowsiness

Many of us recall traveling in the back seat of an old station wagon and feeling sleepy shortly after getting on the highway. This was not by accident; car cabs and machine cabs were not designed to provide continuous intake airflow. Until recently, automotive cabs did not include CO2 sensors or automatic fresh air intake systems that would activate when the CO2 levels went beyond a safe level.

While things have improved over time, many modern operator cabs still have deficiencies. In many designs, operators can put the machine into full recirculation mode, which has been considered the best way to keep dust out of the cab, however, it endangers the operator whose breathing is continually increasing CO2 levels.

Monitoring open/shut eyes through cameras may be an effective means of identifying drowsiness, but it fails to identify the causes of operator drowsiness. ISO 23875 focuses on engineering controls to maintain a constant airflow and the means to test the system's effectiveness, along with a robust CO2 monitor to give real-time indications of CO2 levels to the operator.

It's time to wake up to the fact that when CO2 is allowed to concentrate, operator sleep events will occur. ISO 23875 addresses an in-cab air environment cause of operator drowsiness and reduces operational risks for the operator and the mine site.

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