Carbon monoxide accumulation and oxygen depletion during butane heater operation in an enclosed tent

Abstract Carbon monoxide (CO) concentrations within a tent may vary with height and duration of heater operation, complicating the interpretation of incident reconstructions. We measured CO and oxygen (O₂) at 0–10 cm and 140–150 cm above the floor during three full-scale trials with a liquefied-butane heater. Paired readings were analyzed at 3-min intervals from 3 to 39 min. Mean CO increased from 40.33 to 93.33 ppm at the upper position and from 8.67 to 101.67 ppm near the floor; descriptive linear slopes were 1.509 and 2.684 ppm/min, respectively. At 30 min, upper-minus-lower differences were − 2, −2 and + 4 ppm. All three differences were negative from 33 min onward. The 3–39 min time-weighted mean nevertheless remained higher at the upper position (62.99 versus 51.10 ppm). Mean O₂ declined from 20.03 to 16.80 vol% above and from 20.90 to 17.97 vol% below. Thus, the early upper CO excess was followed by higher near-floor readings in each trial, with variation in transition timing. These findings show why both measurement height and elapsed time matter when interpreting a tent reconstruction; they do not establish an individual inhaled dose.