Monday's spill is the second in less than a month. Two other workers were injured in an acid spill in mid-February.
This week's accident happened in the same processing unit and involved the same chemical as that incident last month. Tesoro says the similarities end there, but others are not so sure.
"This refinery has got to prove to the community that they're going to follow the safety procedures," Martinez City Councilman Mark Ross said.
Ross is a member of the Bay Area Air Quality Management Board and thinks Tesoro's latest accident is a sign of a larger problem within the refinery. And he says he's been told how two contractors were sprayed by sulfuric acid Monday morning.
"They were using the proper safety gear, but the proper procedures in putting them on and taking off, you have to follow it scrupulously and that probably wasn't done in this incident," Ross said.
A month ago, two other workers were burned by sulfuric acid and they reportedly were not wearing safety gear.
Ross, a former refinery operator, isn't the only one calling into question Tesoro's safety practices and training.
Congressman George Miller spoke with ABC7 News by telephone.
"We're very concerned about the safety precautions in place and very concerned about the management's attitude toward safety and I think the second accident bears out that our concern is well-founded," Miller said.
Last month, Tesoro wouldn't allow inspectors from the U.S. Chemical Safety Board inside the refinery. This time, a CSB team is onsite along with Cal/OSHA inspectors.
As for safety, a Tesoro spokesperson told ABC7 News, "We are committed to developing a culture in which personnel are committed to their own safety and, just as importantly, to each other's safety."
"I'm very disappointed in Tesoro's actions and most importantly I'm concerned that these recent incidents show that there is a safety culture issue that needs to be addressed and the county will look at that," Contra Costa Supervisor John Gioia said.
Tesoro reports that both workers treated in Monday's incident are okay and back at work.