Inmate advocates point out that many prisoners exposed to high temperatures are unable to cool themselves - by taking a cold shower or by sitting in an air-conditioned room - in a way people living outside prison walls regularly do.
"This is not an issue of comfort and luxury," said David Fathi, director of the American Civil Liberties Union's National Prison Project, who has litigated cases in Wisconsin and Arizona to provide appropriate cooling for inmates.
"Prisons have an obligation, which no one disputes, to provide conditions that, while they don't have to be comfortable, they can't be deadly," Fathi said. "But because of climate change, because of the changing population, heat is a deadly risk for many prisons and jails throughout the United States."
The February death of 56-year-old former Marine Jerome Murdough is a jarring lesson in what can happen when cells overheat, even though it differed from the classic inmate heat death in some significant ways: It happened in the winter and was due to malfunctioning heating equipment rather than scorching outside temperatures.
Officials haven't said exactly how Murdough died. A preliminary city Department of Correction probe found the medical examiner investigator believed he died of hyperthermia, noting that "the heat in his cell caused his body to shut down," according to court documents. One official who spoke on condition of anonymity described Murdough as having "basically baked to death."
Heatstroke causes a person's body temperature to increase rapidly - up to 106 degrees within 10 or 15 minutes - and can be fatal if not quickly treated. Other heat-related illnesses - heat exhaustion, rashes, fainting - are most likely to affect elderly and overweight people. Others particularly at risk include people with heart disease and asthma or those, like Murdough, who are taking psychotropic drugs.
Psychotropic medications can impair the body's ability to cool itself by sweating, experts say. That's a particular concern as the number of mentally ill inmates who take such drugs has risen steadily. According to Bureau of Justice Statistics from 2005, the most recent year available, more than half of all jail and state prison inmates had a mental health problem.
Nationally, the bureau doesn't track heat-related deaths in jails and prisons. But they do occur.
A report issued last month by the University of Texas School of Law's Human Rights Clinic found that at least 14 inmates have died from exposure to extreme heat since 2007 in state correctional facilities. And a federal judge ruled in April that a special monitor will be appointed to make sure the heat index doesn't top 88 degrees for death-row inmates at the Louisiana State Penitentiary at Angola.
The courts have likewise ruled that Arizona prisoners on psychotropic medication must be housed in a unit where the temperature is maintained at 85 degrees or below and Wisconsin was ordered to install air conditioning in a so-called Supermax state prison, Fathi said. Courts have also ruled on heat conditions for prisoners in cases brought in Illinois, Georgia and Delaware.
Some corrections officials have argued that upgrading decades-old facilities to be retrofitted with air-conditioning units is costly and complicated. They've also warned that air conditioning certain units, such as punitive segregation units, might encourage prisoners to act out in the hopes of landing a cooler bunk.
In New York City, a court-appointed monitor's expert has said the practice of circulating air in housing units for nearly 600 inmates under 23-hour lockdown behind solid-door cells isn't a sufficient means of cooling, according to court documents in a long-running lawsuit over heat-conditions on Rikers Island.
In court papers filed last month, inmates interviewed by The Legal Aid Society's lawyers during the summer of 2013 - when for seven straight days in July temperatures exceeded 90 degrees - said the oppressive heat made them feel dizzy and delusional and agitated their asthma and other health conditions.
"I feel like I'm dying in the cell," said inmate Freddie McGrier, according to court documents.
Nearly 800 New York City inmates are designated as heat sensitive by health staff and are supposed to be moved within hours to an air-conditioned unit when the outside temperature is above 85 degrees, the DOC says.
In a statement, a DOC spokesman said officials are improving their procedures, maintenance and staff performance to make sure jails are safe.
Alma Murdough, the mother of Jerome Murdough, announced Friday at a news conference that the family plans to file a $25 million wrongful death lawsuit.
"I know he was yelling for help and nobody ever came," she said.