ECE invention may benefit firefighters

After sustaining a certain amount of exposure, carbon filters need to be replaced — the question is how often.

One Carnegie Mellon student has found an answer, and it’s part of work being done at the Carnegie Institute of Technology.

Sarah Bednair’s team is just one of many groups of students working on projects in CIT’s electrical and computer engineering department. One team has been working with accelerometers, devices that can be used to monitor deceleration in cars. Other groups are focused on projects involving micromirrors, which are used in some types of high-definition televisions.

But Bednair’s team has decided to focus on improving the safety firefighters and other emergency workers who use gas masks.

Bednair, a Ph.D. candidate, recently designed a vapor-sensing device that could potentially benefit firefighters.

Her work is part of a four-year project funded by the National Institute for Occupational Safety and Health (NIOSH), the Dowd Fellowship, and the Multidisciplinary University Research Initiative (MURI), which is backed by the Air Force. Bednair has been working with a team of about a dozen other students.

Their objective is to create a sensor for the carbon filters in masks worn by firefighters. Rescue workers are frequently exposed to toxic gases such as carbon monoxide, and they rely on the filters in their breathing respirators for protection. But these filters eventually wear out.

“The problem is right now it’s very arbitrary how often they throw away cartridges,” said Bednair. “There’s no way of determining when the lives of these filters are over.”

Scientists have created models to help predict an answer to this question, but their data does not take into account the fact that different firefighters encounter different levels of toxic gases. It is impossible to determine the life of a carbon filter at an invariant amount of time.

“It’s an accumulation level of exposure,” said Bednair. “The problem is that they don’t know what they’re being exposed to and what are the concentrations.”

This flaw that was present in the original filter system first caught the attention of NIOSH after the September 2001 attacks on the World Trade Center.

“They ran out of cartridges,” Bednair said. “They didn’t have the means to know when the service life was over, so they just picked an arbitrary time, a few hours or something.”

Bednair created a mass-sensitive device that monitors the service life of the cartridges. “We want to integrate all different types of sensors onto a single chip,” she said.

The device begins at a set mass. When on, the device oscillates at a regulated frequency as surrounding air passes through the carbon filter.

The device also consists of a sensitive outer layer that is set to absorb certain gases. As it absorbs the gases, the device becomes heavier.

The mask detects the mass of the oscillating device. When it becomes heavy enough to indicate that the cartridge is spent, a signal indicates to the firefighter that it needs to be replaced.
But the process of developing the device has not been without setbacks. For one thing, the team has had some trouble with temperature rejection.

In any given climate, the temperature is never a constant value.

Everyday fluctuations in weather and humidity can affect the accuracy of the device.
Even the humidity in a firefighter’s breath is a factor that has to be considered.

“It’s a challenge,” Bednair said. “How do you reject these changes that you see every day?”
Bednair has also been struggling to integrate the outer layer to the mass-sensitive device.

“You can’t stick a mass sensor out in the air without putting a sensitive layer on top of the mass sensor,” she said. Bednair had to make the sensor smaller in order for it to function inside the outer layer.

As soon as Bednair finds solutions to the current problems, her device will be ready for use nationwide. Each sensor will cost only about a dollar.