How much HF Acid is needed to cause a fatality by contact

Employee #1 was mixing an automobile cleaning solution, which required that several chemicals to be added to a mixing tank. He would first weigh out the appropriate amount of a chemical and then use a chemical transfer pump to move it into an empty drum until the desired amount (by weight) was obtained. This task was repeated for each of the chemicals involved. At the time of the accident, Employee #1 was using an old chemical transfer pump to move hydrofluoric acid solution when the hose joint failed. The hose appeared to break away, and hydrofluoric acid, sprayed out onto Employee #1.

He ran to the emergency shower, where the solution began to react with the water, the concrete floor, and his skin, creating a cloud of hydrogen fluoride gas that immediately obscured the area.

Employee #1 inhaled the vapors, and over 20 percent of his body had been contaminated by the hydrofluoric acid spray.

A coworker made Employee #1 remove his clothes while he and another coworker tried to wash him down. Apparently Employee #1 then went back into the gas cloud to turn off the chemical pump.

Emergency Services arrived on the scene and treated Employee #1. While he was being transported to the hospital, Employee #1 began to have problems breathing and wanted to sit up. The moment he did, he vomited sputum several times and then went into respiratory arrest. All efforts to resuscitate him were ineffective, and he died before arriving at the hospital.

At the time of the accident, Employee #1 was not wearing any personal protective equipment. Three days before the incident, the company had received a new chemical transfer pump, which was scheduled to replace the one that failed.

Approximately 20 gallons of hydrofluoric acid were released from the drum onto the concrete floor.

Source: https://www.osha.gov/ords/imis/establishment.inspection_detail?id=109145631