There are a lot of horror stories about HF. Take them seriously. (Click <here> for First Aid procedures for HF exposure to skin). In brief:

1. Concentrated HF is considered "extremely" toxic (4, on the health hazard scale of 0-4). However, any solution containing a source of free fluorine ions is also hazardous. A plain, concentrated ammonium fluoride solution is considered "very" toxic (3, on the health hazard scale), yet becomes "extremely" toxic when made more acidic, such as in the BOE mixtures we use at SNF. So, even though 20:1 BOE has much less HF (about 7% of volume) than 49% HF, because it also has about 38% NH4F and it is acidic, it presents the toxic hazards as 49% HF.

2. On contact, very HF easily passes through skin and tissue. Because its action can be delayed for many hours, it can distribute throughout the body.

3. Negatively charged fluorine ions bind very easily to positively charged calcium and magnesium ions to form insoluble salts (CaF2 and MgF2 salts form some natural gemstones.) In the body, Ca and Mg ions are used to mediate a variety of physiological processes, such as muscle movement. Calcium is also a chief component in bone.

• Local tissue damage (and the point of contact) results from free hydrogen ions which causes corrosive chemical burns and free fluorine ions which cause deep tissue damage including erosion of bone.
• Systemic damage can occur when fluorine becomes distributed throughout the body. These conditions include hypocalcemia (loss of calcium) and hyperkalemia (too much potassium). Since calcium and potassium regulate the heart, irregular beating and cardiac arrest are manifestations. "Deaths have been reported from concentrated acid burns to as little as 2.5% BSA [body surface area exposed to skin contact]."

4. Calcium gluconate is used as an antidote. This provide extra calcium ions which can scavenge free fluorine ions before they penetrate and damage tissue. In cases of skin contact, calcium gluconate gel must be applied immediately to the area of contact. In cases where systemic damage is a risk, calcium gluconate is administered by a healthcare professional in an IV.

5. Pure hydrogen fluoride is an extremely toxic gas which very easily dissolves in water. "Hydrofluoric acid" describes this solution form. HF easily passes between gas and liquid phases; so HF- (and NH4F-) containing solutions will emit toxic fumes. Although SNF lab safety precautions tend to emphasize protection against skin contact with fluoride-containing solutions, remember to avoid inhalation of the fumes by always working under fully exhausted areas of the wet benches.

6. Concentrated HF solutions are used in many household items, such as rust removers.

For more detailed medical info about HF, check the following links:

e-Medicine website on HF burns