A 27-year-old inmate received burns to 3 percent of his body, and was treated and released from an outside hospital, according to Waters. A 30-year-old inmate sustained minor injuries and was also released from the hospital.
Waters said both inmates were released to the state prison system and are in good condition.
California's Division of Occupational Safety and Health launched investigations into the incident on Wednesday, according to agency spokesman Frank Polizzi.
State corrections officials say inmate firefighters are paid an average of $2 a day when they're in fire camps and an additional $1 an hour when they're assigned to an active fire.
Inmate firefighters are often called to help Cal Fire battle big blazes annually.
CDCR has said the inmate firefighting program can save the state up to $100 million a year. Prison officials note that inmates who volunteer as firefighters can get time off their sentences, and they emphasize that injuries to prison firefighters are rare.
But in the last 18 months, three California prison firefighters were killed on the job.
Those deaths, and in general the use of inmates to help the state battle big blazes, have renewed criticism from criminal justice advocates.
"If these prisoners can be trusted to be running around outside with axes and chainsaws, maybe they didn't need to be in prison in the first place," said David Fathi, director of the ACLU's National Prison Project.
Most prisoners want to work, and jobs for inmates can be a very positive thing, Fathi said.
"But given the vast power disparity between prisoners and their employers, there is also a real risk of exploitation and abuse," he said.
Fathi said inmates are a uniquely vulnerable workforce.
"There's very little in prison that is truly voluntary. So when prisoners 'volunteer' for dangerous work like fighting wildfires, it's critical to ensure that they're making a free and uncoerced choice, a choice that is fully informed about the risks and dangers of the work they're agreeing to do."
Some critics claim that inmate firefighters are not allowed to work for Cal Fire after they're released from prison.
Prison officials say that's not true. They say having a felony conviction does not disqualify a person from employment with Cal Fire.
"It's very unfortunate that there is so much misinformation out there," Waters said in an email, pointing to a press release the agency put out over the summer, highlighting that two former inmates got jobs at Cal Fire.
State officials have yet to respond to questions about their rules associated with employing inmate firefighters after they're released from state prison.
KQED has profiled inmate firefighting crews in the past, and produced the following video detailing their work.