[COVID] damages the lungs, and the crush of patients in hot spots such as Los Angeles; the Navajo Nation; El Paso, Texas; and in New York last spring have needed high concentrations of it. That has stressed the infrastructure for delivering the gas to hospitals and their patients. The strain in those areas is caused by multiple weak links in the pandemic supply chain. In some hospitals that pipe oxygen to patients’ rooms, the massive volume of cold liquid oxygen is freezing the equipment needed to deliver it, which can block the system.