Four (4) workers were injured at a worksite on April 30, 2024, while offloading flammable solvents from a vacuum truck into a storage tanker. At the same time, other workers positioned a hydrovac truck in an adjacent bay to offload a wastewater-and-slurry mixture. During this process, flammable vapors were released and drawn into the idling hydrovac truck’s air intake. This created an ignition source, causing a flash fire between the trucks and injuring the four workers.