CO Sensor System Project: Special Operations

CO Sensor System Project

As firefighters, we know that we are often exposed to hazardous toxins during everyday operations such as when operating at structure fires, car fires, or even when near the exhaust of a fire truck. Of course, we have our personal protective equipment such as turnout gear and self-contained breathing apparatus (SCBA) to help us, backed up by education, training, and guidelines for operating practice.1,2 But we also know there is a lot of judgment involved in applying our guidelines and lots of uncertainty; after all, in many cases we are dealing with an invisible but deadly enemy.3-7

For more than a year, I had a unique opportunity to work on a project that allowed me to get new insights and hard information about the threat that is carbon monoxide (CO). In this article, I will describe the project, which involved developing and testing a “real time” and “around-the-clock” CO monitor prototype and some of the insights that the outcomes of even the first few tests have already produced. If these outcomes hit you as they did me, you will further increase your vigilance and caution when it comes to CO.

Background and Challenge

CO is an asphyxiant gas that inhibits the transport of oxygen from the lungs to the rest of the body by attaching to the blood’s hemoglobin, creating carboxyhemoglobin. Because CO has a much higher affinity for hemoglobin than oxygen, exposure to even low levels of CO can begin to deprive the body of adequate levels of oxygen.

As previously mentioned, we have our SCBA to protect us from CO during rescue and fire attack operations, but it is not always clear as to when the danger is present and thus when to don our masks. For example, what is the hazard during initial size-up? Is there a hazard just outside or on entry to a building in which the fire is deeply seated? How soon after a successful knockdown can masks be doffed?

Many standard operating practices call for spot checking of the environment by a safety officer to determine the need for SCBA use. But we all know that there just isn’t enough time or staffing on the fireground to allow for being followed around with a meter for minute-by-minute CO status readouts.

A prime example of an environment where CO is commonly present is overhaul, where firefighters have already knocked down the fire but are still working to expose hot spots for extinguishment. Tasks during overhaul are typically very physically demanding, such as pulling ceilings down and breaking open walls. Firefighters will often remove their SCBA face pieces to enable greater maneuverability and improved communications, thus potentially exposing themselves to CO among other toxins. For this reason, many departments require use of a multigas meter to determine if the air is safe to breathe. But again, these spot checks are just that, spotty. During overhaul, when materials are being pulled apart and new hot spots are exposed, conditions can change rapidly.

It would be best if each of us could wear a monitor that was always on, always providing an alarm if our masks are off and should be donned. However, because of the extreme temperatures, humidity, and a mixture of gas components on the fireground, especially near the seat of the fire, the sensors used in these devices are often incapable of properly measuring the target gases both in the fire environment and then later. That’s because the electrochemical sensors that are at the heart of common monitors are incapable of rapid recovery from, and more often just survival of, the conditions near the fire.

As no device currently exists to accurately and reliably measure CO during all phases of fireground activities, the research project was undertaken to develop a monitor that could survive and continuously measure CO levels during all firefighting activities and capture enough information that we get the clearest picture we have ever had about the CO threat to firefighters, around the clock.

CO Sensor System Project

Supported by an Assistance to Firefighters Grant from the Federal Emergency Management Agency (FEMA), faculty in the Center for First Responder Technology at Worcester Polytechnic Institute (WPI) undertook the construction of CO and hydrogen cyanide (HCN) monitors with some very special capabilities. At the time, I was enrolled as a graduate student in WPI’s Department of Fire Protection Engineering and became a member of the research team that would develop this device.

The goal of the research project was to capture real-time toxic gas concentrations in the direct vicinity of a firefighter throughout all phases and operations on the fireground using a purpose-built, proof-of-concept, prototype wearable monitor. While the project did work with HCN as well, I will focus on the CO monitor. A prototype carbon monoxide sensor system (CMSS) device was designed and tested that provides reliable and uninterrupted CO data when operating anywhere on the fireground. In addition to measurements of CO, the monitor was designed to capture SCBA mask status to determine an approximate measure of the cumulative unprotected exposure of the firefighter to CO. Evaluation of the sensor was conducted by instructors at the Massachusetts Firefighting Academy (MFA) and by more than 50 on-duty firefighters in the city of Worcester (MA).

The custom-built CO monitor that resulted from the research effort used several innovative engineering solutions to provide continuous monitoring capability under extreme conditions. These included a heat exchanger; a thermoelectric cooler; and a microprocessor controlled pump system, which monitored the temperature of the gas and regulated the rate of gas flow to protect the core sensor. The device can operate continuously without damage in an atmosphere at 260°C (500°F).

The monitor was developed and tested in several phases, with each monitor more rugged and smaller than the ones before. The final size of the unit measured 190 millimeters × 75 millimeters × 55 millimeters (7.48 inches × 2.95 inches × 2.17 inches) and weighed 1,238 grams (2.73 pounds).

The monitor has several features beyond simply measuring the CO and providing a visual and audible alarm when CO levels exceeded a preset value. The device records the measured data once every two seconds and stores that information to an internal memory. Sufficient memory and a battery of sufficient capacity were used so that the devices only needed recharging and data downloading every 36 hours after continuous use. So the devices could and were operated continuously, no events and no parts of the firefighter’s duties were missed. Additionally, a tiny wireless transmitter was inserted into the headband of the firefighter’s helmet. This allowed the monitor to capture and record the presence or absence of the SCBA mask.

Initial proof of concept laboratory testing ranged from controlled gas exposures to live fire testing in the WPI Fire Protection Engineering Department’s fire performance lab. Initial laboratory experiments exposed the CMSS to known concentrations of CO to ensure sensor accuracy. Later testing in the fire lab verified the sensor’s ability to measure CO in harsh environments. During these tests, the CMSS was attached to a crane and inserted into two fire compartments, as seen in Image 2. One compartment was used to expose the CMSS to high temperatures and the other compartment was used to expose the CMSS to high levels of humidity, varying levels of CO, and large amounts of soot and particulates.

Evaluation During Training Exercises

Following controlled laboratory testing, the devices were brought to the MFA and the Worcester Fire Department for field testing and firefighter evaluation.

During the training program at the MFA, recruits must complete a final live fire evaluation that simulates a response to a multistory residential structure. The recruits are broken into several companies, each supervised by an MFA instructor. Throughout the day, a total of three evolutions take place, allowing the recruits to cycle through each of the three company types, engine, truck, and rapid intervention, with tasks covering fire suppression, search and rescue, and ventilation. Because of the controlled nature of these evolutions, it proved to be a prime opportunity to evaluate the CMSS and receive firefighter feedback on the use of the device.

At the beginning of the training day, five instructors, varied across the types of companies, were equipped with a device. Image 3 shows values recorded by one CMSS being worn by an MFA instructor leading recruits in engine company tasks. It is at this location that the firefighters have an exposure to CO as they prepare to mask up near the entrance, which is a common practice in the fire service. An example of results found at this exposure is shown in Image 4, where the device measured CO levels exceeding 1,500 parts per million (ppm) before the firefighter put his SCBA mask on; in fact, it measured more than 1,000 ppm for nearly three minutes. Consider these values in light of the fact that the National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit as an eight-hour time-weighted average for CO is 35 ppm and a ceiling value of 200 ppm and that 1,200 ppm is considered immediately dangerous to life or health (IDLH).9 This shows that firefighters can be exposed to significant levels of CO in situations deemed as ordinary and nonlife-threatening.

On-Duty Firefighter Evaluation

Following evaluation at MFA, 14 devices were deployed to the Worcester Fire Department to be worn at all times to real emergency responses. A total of four companies across the city wore the devices to every response for a two-month period. In total, more than 50 firefighters participated in the deployment, collecting crucial data. During the two-month period, 17 exposures to elevated levels of CO were documented. These exposures occurred across a very wide range of calls including first responder calls and structure fires.

Image 4 shows levels of CO measured by one device during a structure fire. This took place in a four-story residential building with heavy fire on the fourth floor. The CMSS was worn by a firefighter conducting search and rescue operations on the floor beneath the fire, floor three. As shown by the vertical line around 450 seconds, the firefighter was wearing his SBCA while operating within the structure. However, when interviewed later, this firefighter said that smoke conditions were very light. This is another demonstration that smoke conditions are not an indicator of the presence of toxins and that measurements should play a role in determining when to remove SCBA protection.

Image 5 shows an example where elevated levels of CO were recorded while the CMSS device was attached to an SCBA stored in a truck at the station. The CMSS recorded levels of CO for a short time (approximately one hour) nearing 100 ppm. While we are not aware of the specific cause for the elevation at that time, and while it is not above NIOSH or Occupational Safety and Health Administration thresholds for short-term or eight-hour, time-weighted average exposures limits, this demonstrates that firefighters are at risk of low-level exposures even in nonemergency situations. This serves as a reminder of the need for persistent vigilance by the firefighter and the need to apply care in all operations conducted on and off the fireground.

Implications for Policy and Practice

While SCBA use is often a hot topic when it comes to its use in situations without heavy smoke, even the limited data presented within this article show that a firefighter can be exposed to elevated levels of CO during training exercises, structure fires, or even within a fire station. It is also clear that levels of CO during structure fires greatly exceed IDLH conditions, even when there is high visibility in low-smoke conditions, reinforcing the need for respiratory protection even when smoke conditions are low or not present. These data further reinforce the idea that we often read but rarely can see demonstrated: The use of SCBA should never be based on the presence of smoke but rather should be informed by the use of CO measuring devices.

Be careful out there; I know I will be more so than ever before.


Funding was provided through DHS/FEMAs Grant Program Directorate for Assistance to Firefighters Grant Program-Fire Prevention and Safety Grants, grant number EMW-2011-FP-00991. Thanks to the project’s principal investigators at WPI, Professors David Cyganski, R. James Duckworth, and Kathy Notarianni. Additional thanks to the Massachusetts Firefighting Academy, the Worcester Fire Department, and the Fire Protection Research Foundation for their valuable assistance.


1. Shoebridge, Todd, “Carbon Monoxide & Hydrogen Cyanide Make Today’s Fires More Dangerous,” Firefighternation, February 14, 2012,

2. Bledsoe, Bryan, “The Perils of CO,” FireRescue, September 2007.

3. Tippett, John B, “Near-Miss Reports Highlight Prevalence of CO Dangers,” FireRescue, August 2011.

4. Staff, “LODD Report: Deputy Fire Chief Dies When Floor Fails,” Firefighternation, May 31, 2009,

5. Staff, “LODD Report: Career firefighter died while exiting residential basement fire,” Firefighternation, March 20, 2009,

6. Staff, “NIOSH Report: Maryland Row House Fire: Career firefighter dies in residential row house structure fire in Maryland,” FireRescue, November 2008.

7. Staff, “NIOSH Line-of-Duty Death Report: A career firefighter was killed & a career captain was severely injured during a wildland/urban interface operation in California,” FireRescue, November 2006.

8. Madrzykowski, Daniel, and Steve Kerber, “Go with the Flow: NIST study proves PPV can save lives & improve safety” FireRescue, November 2009.