Research finds prototype generators emit less CO

Portable electric generators retrofitted with off-the-shelf hardware by the University of Alabama (UA) emitted significantly lower levels of carbon monoxide (CO) exhaust, according to the results of tests conducted by the National Institute of Standards and Technology (NIST) for the US Consumer Product Safety Commission (CPSC).

Compared with standard portable generators, CO emissions from the prototype machines were reduced by 90% or more, depending on the specific hardware used and operating conditions.

Unintentional CO poisoning claims a number of lives and also leads to many hospitalisations each year due to exposure to toxic levels of the colourless, odourless gas. Many of these deaths and illnesses stem from unsafe use of portable generators.

The tests performed by NIST compared two commercially available gasoline-powered generators against two similar machines that UA retrofitted with closed-loop electronic fuel injection and a small catalyst. Tests were conducted at NIST’s manufactured test home, with the generator operating in the attached garage so as to simulate some common scenarios that often result in deaths or injuries.

In one series of comparisons, generators operated three or more hours in the garage with the garage bay door open and the entry to the house closed. For the stock generator tested, CO levels in the garage peaked at 1500 parts per million (ppm, which are equivalent to microlitres per litre) and inside the house ranged between 150 and 200 ppm.

Clinical symptoms of CO poisoning, including headaches, nausea and disordered thinking, begin appearing at exposure levels of 100 ppm after at least 90 minutes of exposure. During the NIST tests, emissions from the prototype generators ranged from 20 to 30 ppm in the open garage and from 5 to 10 ppm in the house.

CPSC staff conducted health effects modelling using NIST’s test results, as part of CPSC’s technology demonstration program of the prototype generator, to show that its engine’s reduced CO emission rate is expected to result in fewer deaths by significantly delaying the onset and rate of progression of CO poisoning symptoms compared to the stock generator.

On the basis of results of findings from NIST’s two earlier studies, the Centers for Disease Control (CDC) advises to never run a generator less than 6 metres from an open window, door or vent where exhaust can vent into an enclosed area. Steven Emmerich, the lead NIST researcher, reminds that generators should always be operated outdoors, far from open windows.

In their study, NIST researchers also validated the use of their CONTAM computer model for studying the performance of prototype generators under a wider range of conditions than those tested. Results of simulations carried out with this publicly available software for studying building airflow and indoor air quality were checked against measurements of CO levels in actual tests. The predicted results were in good agreement with the CO measurements.