Parametric Evaluation of the CFK and the MIL-STD-1472 Equations as Tools for the Estimation of Blood COHb Levels

Carbon monoxide (CO) is a colorless, odorless byproduct of incomplete combustion that binds to hemoglobin to form carboxyhemoglobin (COHb), impairing oxygen delivery and causing systemic hypoxia. Two widely used models for estimating CO toxicity are the Coburn-Forster-Kane (CFK) equation, which incorporates physiological and anthropometric parameters, and the workload-based MIL-STD-1472 model, developed in the late 1960s and 1970s. Both have been applied extensively in military armored motor vehicle (AMV) operations, firefighting, and mining. This study evaluates the predictive performance of these models during field trials involving AMV crews conducting live-fire exercises. Ambient CO concentrations were continuously monitored, and serial blood samples were obtained for COHb determination. Individual physiological and anthropometric data were used to generate CFK-based predictions, while the MIL-STD-1472 estimates were derived using the activity level equivalent (ALE) values, which were developed to allow for mathematical alignment between the two models. Measured COHb levels showed strong agreement with predictions from both the CFK and MIL-STD-1472 equations. An ALE analysis indicated that the actual physical workload during AMV operations was substantially lower than the activity level (AL = 4) originally recommended in MIL-STD-1472. In addition, algebraic rearrangement of the MIL-STD-1472 equation enabled the estimation of COHb recovery time following cessation of exposure. This study provides a field-based evaluation of two established models for predicting carboxyhemoglobin formation. Measurements obtained during live armored motor vehicle operations demonstrate that both the CFK and MIL-STD-1472 equations accurately estimate COHb under conditions of near-ambient oxygen tension and minimal CO₂ accumulation. Importantly, MIL-STD-1472 predictions using moderate ALE values were more consistent with the observed COHb values, suggesting that the commonly applied activity level (AL = 4) may overestimate CO exposure risk in comparable operational environments.