Yet according to SFDPH spokesperson Imelda Rayes, there are now approximately 300 (registered) mobile food facilities in San Francisco. That means the number has nearly tripled since the mere 120 registered MFFs that were scouring the streets in 2009. What they lack in horse power, the generators may make up for in sheer multitude.
"In a period of three years, the number has increased almost 250 percent and [we're] still getting more applications," she said.
In addition to cumulative impacts, there are also questions about the health impacts on food truck employees.
Studies like such as the 2009 "Modeling the Effects of Outdoor Gasoline Powered Generator Use on Indoor Carbon Monoxide Exposures" by academics Liangzhu Wang and Steven Emmerich brings up a different concern: gasoline generators create emissions of poisonous carbon monoxide.
"The generators are always positioned outside of the vehicle. The workers are inside," Lee said. "We would not expect that there is significant employee exposure to the generator exhaust to the employees."
Yet the U.S. Centers for Disease Control and Prevention (CDC) reported that half of non-fatal carbon monoxide poisoning incidents in the 2004 and 2005 hurricane seasons were due to the gas-powered generators used to heat homes, even when placed outside the homes themselves.
Food truck generators, given their smaller size, are often placed much closer to the trucks and their workers than in the case of houses and their inhabitants. Furthermore, the trucks often idle for long periods to keep the food warm and utilities working.
"At this point, it's enough of a new thing...We're interested in finding out more about them, but at this point we are not receiving many complaints," Richardson said. "A lot of variables are involved. It's something I think we will be doing more research on."
After the game of verbal hot potato that was research for this article — it seems every agency deferred to another in terms of exactly who is monitoring these things — Swanton assured us that the danger doesn't seem imminent.
"In general, small engines [portable generators] are dirtier than an engine providing motor power to a vehicle," he said. "But the sheer number of these cleaner engines dwarfs everything."
True, but the food trucks that run for more than a few hours at one location are increasing in numbers at a rapid pace. With the high number of mobile food trucks in operation, most of which utilize some form of generator or another, it may be time to nail down those pesky variables involved and draw some conclusive evidence on the potential environmental and health effects of our city's seemingly innocent snack time.