In response to the COVID-19 pandemic, hospitals across the United States are disinfecting N95 masks by placing them in repurposed rooms or shipping containers injected with a disinfectant known as vaporized hydrogen peroxide, or VHP. A new tool from the National Institute of Standards and Technology (NIST) can help hospitals and medical professionals determine which rooms should be used to disinfect N95 masks. The tool estimates the amount of VHP masks would receive and suggests that larger rooms containing fewer objects, with less-reactive surfaces and slower ventilation, maintain VHP concentration the best.