Hard-Hat Sensor Short-Circuits Carbon Monoxide Poisoning

CO poisoning is insidious, quickly producing nausea, fatigue, headache, and disorientation, followed by unconsciousness and, too often, death. Extending the electronic measurement of our lives into the workplace, researchers at Virginia Tech combined wearable computing and prevention-through-design to develop a practical sensing and alarm system that can tell when a worker’s blood oxygen level is cratering and prevent carbon monoxide poisoning.

The result was a standard construction hard-hat modified to include a non-invasive blood-oxygen monitor. This week, the authors—Jason B. Forsyth, Thomas L. Martin, Deborah Young-Corbett, and Ed Dorsa—received the IEEETransactions in Automation Science and Engineering’s Best Paper Award for their efforts.

The design combines a pulse oximeter (the Nonin Xpod), a small radio transmitter (the Digi Xbee), a nine-volt battery and a 3.3-volt regulator, all tucked into a package that adds very little weight to a standard hard-hat. The LED/sensor package keeps watch through a small window cut in the front of the helmet’s headband. The headband turns out to be one of the trickiest parts of the design: It has to keep the sensors in position over a consistent spot on the wearer’s forehead, without being so loose that the sensor shifts with the user’s every movement, or so tight that it interferes with blood flow in the skin.

The pulse, in this case, refers to the cardiovascular pulse rather than an electromagnetic pulse. The pulse oximeter uses two LEDs—one emitting red light at 660 nm and another shining infrared at 910 nm—with a photodiode that measures the radiation reflecting back from the skull beneath the skin.  The amount of blood in the capillaries and vessels beneath the skin varies during the circulatory pulse, as does the oxygen saturation (and hence the color) of the blood. Bright red, highly oxygenated blood (HbO2) absorbs more infrared light. Dark red, deoxygenated blood absorbs more red light.

The algorithm tracks the relationship between variations in the intensities (I)of the red and infrared reflections to create a very close index of the fluctuations in the total blood oxygen saturation. Since I can’t resist, the index, R, is

R = ln (Ired minimum / Ired maximum) / ln (Iinfrared minimum / Iinfrared maximum)

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Source: spectrum.ieee.org