There seems to be more to the story of some noxious tear gas that leaked out of a building where an SF Sheriff's Department training exercise was going on last week in San Bruno.

We learned last Wednesday that, a day earlier, 20 students and one teacher at Portola Elementary School in San Bruno experienced eye irritation and were sickened by tear gas that had wafted over to the school from SF's nearby County Jail #5 facility on Moreland Drive in San Bruno.

There had to have been a significant amount of the noxious gas used, as we're now learning that the gas canisters were being emptied inside of a building, and yet enough of the stuff managed to leak out that it traveled a half mile to reach the school and cause symptoms in 20 kids. At least one child, who has asthma, experienced a severe reaction, as KTVU reported last week.

As the Chronicle reports, the Bay Area Air Quality Management District and San Mateo County Environmental Health Services are both investigating the incident now. And the Sheriff's Department may still have some more explaining to do about the substances that were in use.

The paper discovered through an anonymous source that this training exercise, which was meant to test the effectiveness of the department's gas masks and riot gear against such chemical agents, involved campus police as well from UC Berkeley and UCSF. Those officers "were invited to bring any chemical agents in the campus police forces’ inventory so they could be disposed of during the exercise," as the Chronicle reports, and some of these gas canisters had reportedly sat in storage since the 1960s.

The Sheriff's Department has said only that the two substances that were used in the exercise were CS gas (2-chlorobenzylidene malononitrile), a common riot-control agent that can cause respiratory symptoms; and OC gas (oleoresin capsicum), aka pepper spray. But it's anyone's guess what the formulations may have been in the 50+-year-old cannisters they were playing around with, or what may have happened to the gases over time.

The Chronicle spoke with Emanuel Waddell, a professor and chair of nanoengineering at North Carolina Agricultural and Technical State University in Greensboro, who suggested the chemical makeup of the substances could have changed depending on how they were stored. And, Waddell said, "They could become less toxic [over time], and there’s a chance they could become more toxic."

SF Sheriff Paul Miyamoto has expressed some mild regret about the situation, and under questioning from the Chronicle, he said of the old gas cannisters, "Obviously we are always concerned that there's something expired or out of commission, to how we dispose of that."  He added, "It's a part of what we're going to look into as part of our review, making sure that it doesn't happen again."

Previously: SF Sheriff's Exercise Involving Pepper Spray Sickens Elementary School Students

Top image:  A US-made CS gas canister used by Haitian police to disperse demonstrators in Haiti on September 14, 2023. (Photo by Giles Clarke/Getty Images)