White Paper: Orthogonal Detection Can Help Save Firefighters Lives in the Overhaul Stage of Operations

What Is the Overhaul Stage of Firefighting

Overhaul is the stage of firefighting when firefighters check for the presence of fire in both precontrol and postcontrol phases. Because of the lack of visible fire and smoke during this stage, firefighters are likely to remove Self Contained Breathing Apparatus (SCBA) and work “barefaced.” The overhaul stage formerly was considered less toxic than suppression activities.  However, the increased use of plastics as a construction material has increased the likelihood of complex inorganics toxic gases not detected by Carbon Monoxide (CO) and Hydrogen Cyanide (HCN) detectors.

Orthogonal Detection Can Provide More Complete Protection From Toxic Gases and Vapors

Building materials, furnishings, paints, plastics and the electronics used in today’s buildings have the potential to burn or decompose into acutely and chronically acting toxic gases and vapors.  Studies have validated that toxic gases and vapors are not just present during suppression activities but also during the overhaul and investigation stages.  Many potentially toxic and carcinogenic gas and vapors can or will be present during the overhaul process.  They include but are definitively not limited: Carbon Monoxide (CO), Hydrogen Cyanide (HCN), oxides of Nitrogen (NO and NO2), Sulfur Dioxide (SO2), Polycyclic Aromatic Hydrocarbons (PAHs), Aldehydes (like Formaldehyde), acids (like HCl), aromatics (like benzene) and Phosgene (from the thermal decomposition of refrigerants).  Even a small kitchen fire can off-gas many toxic vapors from pots and pans when Teflon thermally decomposes including PFIB (perfluoroisobutane, similar to a chemical warfare agent) and HF (hydrofluoric acid).

CO and HCN Cannot Work as “Canaries”

Standard CO detectors have been used to indicate the presence of toxic gases.   However, there is no significant correlation between CO levels and levels of other chemicals that may be present during overhaul. Electrochemical cells used to measure CO are also prone to give inaccurate readings in the presence of interferants or high humidity.

The Value of an “Orthogonal” Solution

 “Orthogonal” is used to characterize vapor detectors that use multiple, non-redundant sensors to solve a detection problem. The Environics ChemPro100i is an orthogonal detector. The primary sensor is an open-loop Ion Mobility Spectroscopy (IMS) sensor. It uses data from the IMS sensor with additional sensors and computer “fuzzy logic” to classify chemicals. The ChemPro100i orthogonal system has the proven ability to give a warning for more threatening chemicals in the overhaul environment than any other handheld detection technology. The ChemPro100i also does not have the calibration and sensor replacement costs that are associated with CO, HCN or similar sensors. The ChemPro100i also comes with a 5-year Guaranteed Cost of Ownership (GCO) program.  Normal maintenance costs are completely covered for the first 5 years of ownership. The ChemPro100i represents a more systematic approach to monitoring the overhaul process for toxic gases and vapors. If a toxic gas or vapor is present, it alerts to “mask up” and defeats the desire to remove SCBA.

The ChemPro100i...

Overhaul Library

The Overhaul library in the ChemPro 100i has two “baskets” of data.  “Mask Up” measures 19 of the most common Overhaul chemicals such as Acrolein, Benzene, Formaldehyde, CO, HCN etc. at TWA levels. The other “basket” is a generic “Chemical Detected” alarm for when the detector’s orthogonal sensors record a potentially dangerous chemical that is not in the “Mask Up” group.  “Chemical Detected” covers hundreds of toxic chemicals, thus providing an extensive, additional, level of safety for the user.

What the ChemPro100i Tells You, What the ChemPro100i is Detecting

The Overhaul library provides a “Mask Up” (above Table) prompt for personnel to put on their self-contained breathing apparatus (SCBA).  It is not meant for chemical classification.   Advanced users my obtain additional information about the atmosphere by using the “TIC-Classifier” or “TIC Confirm” libraries.

The “Trend” screen...

Radiation Detector (RAD) Module and Other Accessories

The RAD module brings additional capability to the ChemPro 100i– it permits measuring hazardous gamma radiation at the same time as vapor monitoring. The ChemPro100i also can use a handy ”Sampling Cap” that allows for collecting an air sample. The Sample Cap fills a Tedlar bag using the ChemPro air inlet. 


About Us & ChemPro100i

ChemPro 100i is a product of Environics, fielded in more than 50 countries and widely used among Hazmat teams in the US and Canada. Environics has been present in the US since 1988 and now is represented by Gases101 LLC, Round Rock Texas. Please contact us for further information.

Master Distributor in the US
Gases 101 LLC
1107 Wonder Dr, Round Rock
TX 78681
+1 512 436 8923

Environics Oy
Timo Jaakkola
Sammonkatu 12
50100 Mikkeli – Finland
US Cell +1 443 703 8008


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  • Michael Donahue, “Occupational Safety and Health Programs for Fire Investigators,” Fire Engineering, 2/2001 

  • F.D.J.R. Feunekes, F.J. Jongeneelen, H. v.d. Laan, F.H.G Schoonhof, “Uptake of Polycyclic Aromatic Hydrocarbons Amount Trainers in a Fire-Fighting Training Facility,” AIHA Journal, 1/1997 pp. 23-27 

  • John R. Hall, “Whatever Happened to Combustion Toxicity,” NFPA Journal, 11- 12/1996, pp. 90-101 

  • Gregory Kinnes, Greg Hine, “Health Hazard Evaluation Report 96-0171 Bureau of Alcohol, Tobacco, and Firearms”, 11/1997 

  • Dennis L. Rogers, “Characterization of Fire Investigator’s Exposure During Fire Scene Examination,” DuPage County Arson Task Force, DuPage County, IL, March 18, 2005
  • Adapted from Chris Wrenn, Application Note 103, Environics USA Inc 2012.