Abstract: At 1:37 p.m. on May 25, 2021, an employee was working as an airplane mechanic at a hangar at Montgomery Field Municipal Airport. He was using a compressed oxygen cylinder connected to a Hydraulics International Inc. air-driven booster pump to refill an oxygen tank on a small aircraft. The employer had borrowed the booster pump from an acquaintance, as the shop's usual pump was out of service. This replacement pump was of a different model and rated for up to 25,000 psi. After adjusting the oxygen flow, the employee heard an unusual sound from the pump or pressure gauge and approached to investigate. A flash fire ignited near the gauge area, destroying the gauge and connectors. The fire burned the employee's hands, face, and abdomen. The employee was hospitalized for treatment. Investigators noted the presence of oils and other flammable substances in the area at the time of the incident.