Academic Research · Plain-language review
Heat-Related Mortality in U.S. State and Private Prisons
This nationwide study moves beyond the presence of hazardous heat and examines its association with recorded deaths. It asks whether hotter summer days and heatwaves are followed by increased mortality—including suicide—among people held in U.S. prisons.
What the researchers studied
The researchers linked federal mortality records with daily maximum-temperature estimates for state and private prisons during June, July, and August from 2001 through 2019. The analysis included 12,836 deaths at 962 facilities.
Using a time-stratified case-crossover design, each deceased person served as their own comparison. Temperatures immediately preceding the death were compared with temperatures on reference days within the same month and year. This design helps control for individual characteristics that do not change over time and for seasonal patterns.
What they found
Two-day heatwaves were associated with a 5.5% increase in total mortality, while three-day heatwaves were associated with a 7.4% increase. Across the following one to three days, an extreme-heat day was associated with a 22.8% increase in suicides.
The largest increases in mortality appeared among people aged 65 or older, people incarcerated for less than one year, and people in certain geographic settings. The paper reports confidence intervals for every estimate; not every heart-disease or suicide comparison reached statistical significance.
Why this matters to IWP
People in prison generally cannot leave an overheated environment, select different housing, or independently obtain cooling protections. Older adults, people with chronic illness, and people taking medications that affect temperature regulation may be particularly vulnerable.
What the study does not prove
This is an observational study. It identifies associations between temperature and mortality but cannot establish that heat caused every individual death. Temperature was estimated outdoors at each prison location rather than measured inside every housing unit.
The researchers did not have comprehensive information about air conditioning, ventilation, personal access to water or fans, individual medications, or every underlying health condition. Those missing details matter and make transparent facility-level monitoring an important next step.
Access, funding, and data
The full article is freely available under a Creative Commons Attribution licence. The research was supported by grants from the National Institute on Minority Health and Health Disparities and the National Institute of Environmental Health Sciences; the funders had no role in the study’s design, analysis, publication decision, or preparation.
The underlying Bureau of Justice Statistics mortality data are restricted to protect confidentiality, although qualified researchers may apply for controlled access. The article’s methods, reported results, figures, and supporting information are publicly accessible.
Suggested citation:
Skarha, J., Spangler, K., Dosa, D., Rich, J. D., Savitz, D. A., and Zanobetti, A. “Heat-related mortality in U.S. state and private prisons: A case-crossover analysis.” PLOS ONE 18(3): e0281389 (2023). https://doi.org/10.1371/journal.pone.0281389
Continue exploring
Read this paper alongside the nationwide Nature exposure analysis and the JAMA study of extreme heat and suicide-watch incidents. Each answers a different question; together they form a stronger, more careful picture than any one paper could provide alone.