A federal judge is ordering the state to disclose the number of heat-related deaths that have occurred since 1990 in Texas prisons, where less than a third have air conditioning in all housing areas.

U.S. District Judge Keith Ellison at a hearing Wednesday in Houston gave the state 30 days to comply, but not before questioning why its lawyers had not provided the information sooner, the Houston Chronicle reported.

The order comes as part of a federal civil rights lawsuit filed in 2013 that contends at least 13 inmates being held by the Texas Department of Criminal Justice have died of heat-related deaths since 2007, including 11 in 2011 when a heat wave brought some of the hottest temperatures on record.

"We are not talking about how many widgets were sold out of a given factory," Ellison said during the hearing. "We are talking about human lives, and I would be very distressed if the answer is the TDCJ does not even keep count of how many people died of heat-related illness."

The lawsuit argues more than 1,400 prison inmates, most of them elderly and disabled, are suffering "cruel and unusual punishment" by enduring extreme summer heat without air-conditioning.

"The well-being of staff and offenders is a top priority for the agency and we remain committed to making sure that both are safe during the extreme heat," according to a statement by prison spokesman Jason Clark.

There are 109 state prison facilities in Texas, with 30 that are air-conditioned in all housing areas. Clark said all prison units now have at least some areas that are air-conditioned.

But Austin lawyer Jeff Edwards, representing prisoners on whose behalf the lawsuit was filed, said conditions in the prisons have "turned fraud into a death sentence, drunk driving into a death sentence."

If the number of people escaping from prison were as high as the number of people suffering heat-related deaths, Edwards said, "heads would roll and things would change."

Ellison also ordered Texas officials to provide figures on the number of heat-related injuries to staff and inmates at the Hodge Unit, a prison south of Tyler in East Texas that opened in 1995 without any air-conditioning.

Edwards said a key part of the case is to find out what prison officials knew about people being injured or killed by the heat and how they responded.

"It has always been a huge problem in the Texas prison system, and they ought to be able to tell us who died of heat-related illness in the Texas prison system," Edwards said during the hearing, "and if they can’t, they ought to say it under oath."

Department of Criminal Justice officials say a study has determined that just to outfit four prisons with air-conditioning would cost approximately $350 million.