BART is dusting off an emergency plan to deal with a pandemic — and among the possible actions are reducing service or shutting down the trains.

“That would only be a last resort for BART,” said Jim Allison, an agency spokesman. “We are an essential service. We know that many people can’t work from home and that they have no other choice than to use public transportation.”

The agency has long kept contingency plans in case of an earthquake, terrorist attack, pandemic or other grave disaster. It includes staffing recommendations if the rail system is directed to run fewer trains, as well as a procedure to bring trains into the yard and secure the stations. It also includes a protocol for delivering information to riders in real time.

BART officials update it every couple of years, revising contact information or removing names of people who have left the agency, spokeswoman Alicia Trost said.

Though top transit agency staff have been discussing the plan for two weeks, it current has no intention to cut back service or stop running trains. She stressed that these last-ditch measures have nothing to do with the ridership losses BART has experienced as cities cancel events and more people work from home.

A shutdown or service reduction would kick in only if several operators get sick, or if Gov. Gavin Newsom requires transit agencies to stop operating, Trost said. The agency has set up a task force that communicates daily with local, state and federal officials, then reports back to BART’s employees, General Manager Bob Powers said Thursday.

“This is sensitivity thinking — you know, ‘what if’ thinking,” Powers told the BART Board of Directors.

“We’re looking at all of the potential scenarios — we call them ‘triggers’ — both internally and externally, that could impact the level of service that we provide,” said Tamar Allen, the assistant general manager of operations.

An “external trigger” would be an order from the state to reduce service, she said. An “internal trigger” would be operators unable to come to work, either because of illness, quarantine or schools closing.

Allen said BART managers are meeting with the agency’s labor unions to discuss these scenarios. John Arantes, president of the union that represents mechanics and clerical workers, said he will join one of those meetings Friday.

“My members continue to come to work, to keep the system going,” he said in an interview Thursday night. “Yes, we’re concerned.”

In a separate interview with The Chronicle, Powers emphasized BART’s commitment to stay open and keep the trains running.

“We are running at full service, and there is no plan to deviate from that full service,” he said. “If we are directed (to cut service) by the governor or medical professionals, then we need to be ready for that. So we are thinking it through.”

Board President Lateefah Simon said she’s also determined to keep the trains running.

“Everyone needs to be thinking about worst-case scenarios,” she said. “But we still have a lot of people who need to catch the train to get to work. And I’m one of them. I’ll be on the 8:23 a.m. train from Richmond on Friday morning.”

BART is losing up to $600,000 a day in fares from low ridership, a major blow for an agency that relies on fare revenue to cover 60% of its operating costs.

On Wednesday, the agency carried only 268,192 riders — a 35% drop from the average Wednesday in February. In addition to the losses, the transportation agency is paying for extra cleanings, hand sanitizer dispensaries in all 48 stations, and other protections against the coronavirus.

Despite its plummeting revenue, the agency is running 10-car trains during commute periods, which gives people ample space to move around and sit by themselves if they choose. Public health officials are encouraging “social distancing” as a way to avoid spreading the coronavirus.

Just weeks ago, riders stood elbow-to-elbow in packed rush-hour trains. Now, the crowds have thinned, and even the parking lots are empty. Although Newsom’s call to cancel gatherings with 250 people or more doesn’t apply to mass transit, it wouldn’t matter anyway, General Manager Bob Powers said in a statement. Passengers can always stand at arm’s length these days.

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan