Carbon Monoxide Exposure in Workplaces, Including Coffee Processing Facilities

To the Editor:

We read the recent review of carbon monoxide (CO) poisoning by Rose and colleagues (1) with great interest. To their excellent summary, we would add mention of the burden of occupational CO exposure: 13% of nonfatal carbon monoxide poisoning cases seen in U.S. emergency departments during a 3-year period were exposed at work (2), and CO exposure is the leading cause of fatality resulting from acute chemical inhalation among US workers (3). Because CO is odorless and tasteless, patients may not be aware of workplace CO exposures. Thus, it is important for clinicians to be familiar with occupational sources of CO.

Occupations that are known to have greater risk for CO poisoning include jobs that require working around combustion sources such as engines and fires and include mechanics, firefighters, longshore workers, diesel engine and forklift operators, and tunnel or toll booth attendants (3). Other occupations that have been largely overlooked but also carry risk for CO exposure include those as varied as warehouse workers, who use propane or diesel forklifts, and restaurant workers, such as charcoal meat grillers and indoor barbeque workers (4).

People who work at coffee processing facilities that make coffee extract are also at risk for CO poisoning (5, 6). Six workers at a coffee extract facility in Japan become symptomatic after they entered or approached a tank that stored coffee extract. One of these workers died and at autopsy was found to have a carboxyhemoglobin level of 26% (5). Subsequent measurement of CO inside the storage tank showed concentrations of 10,000–100,000 ppm, levels at which lethal carboxyhemoglobin saturation could be achieved in as little as a few minutes (5). At a coffee extract facility in the United States, a worker who entered a storage tank collapsed and was initially resuscitated with oxygen on site; his carboxyhemoglobin level was 27% at the hospital. CO concentration inside the tank was found to be 7,500 ppm (6).

We recently evaluated the potential for CO exposure at a coffee processing facility that makes whole bean and ground coffee, rather than coffee extract. Interestingly, the biggest source of CO was not from the roaster, a combustion source, but rather from the roasted beans themselves. High CO levels were observed where coffee beans were stored or ground. Notably, grinding provides a greater surface area for the off-gassing of CO that occurs after roasting (6). We found workers with personal CO exposure levels that ranged from 7 to 30 ppm when averaged over a shift, with a peak CO level of 584 ppm when a worker was standing next to an open hopper of ground coffee. Although not as high as the concentrations inside coffee extract storage tanks, as noted earlier, these exposures approach or exceed the levels recommended by the National Institute for Occupational Safety and Health (7) and, as Rose and colleagues point out, have potential health effects (1).

Recognizing an occupational source of CO has diagnostic and therapeutic implications for a patient with CO poisoning and provides an opportunity for prevention in coworkers. We encourage clinicians to consider workplace CO exposure when evaluating patients with symptoms and signs compatible with CO poisoning. Our data indicate that coffee processors should be added to the list of occupations at risk.