Answer:
If you mean hydrogen fluoride, that depends on how much you're exposed to at once. The first rule of toxicology is that the dose makes the poison. That being said, the lethal dose at which 50% of test animals die of HF exposure is about 1.3 grams per kilogram of body weight in rats when consumed orally. HF is generally classified as "very toxic" and "corrosive", and is considered an extreme occupational hazard for anyone who works with it.