Of all the faults of dangerous acids, they can usually be counted on to be obvious. Sometimes that’s not the case. Certain acids can travel freely through the body, leaving no burns on the skin but causing massive internal damage.
We’ve talked about hydrofluoric acid before, mostly because it’s very, very scary. It’s used to etch designs into glass and clean steel. It’s also sometimes used in labs to make fluorine compounds. Wherever it’s used, it’s treated with great respect. Hydrofluoric acid, in vapor, can cause terrible damage to the lungs. As a liquid it can eat through flesh, and many other things as well. According to a users guide, exposure to anything over a 50% concentration causes immediate and terrible danger.
In 1996, one sanitation worker died and another was hospitalized after a barrel of 70% solution burst and they inhaled the vapor. In 1980, a lab tech died when the acid, at a similar concentration, burned only 2.5% of his body. Later, another lab technician died when he was burned over 9% of his body—he had to be rescued from a swimming pool, which he jumped into as a way to wash the acid off.
Lower concentrations of the acid have their own terrors. Among them is the fact that exposure to the acid can cause no initial problem. It can sink into the skin, leaving it seemingly unharmed, but move through the body. In some cases, it can get into a person’s body through their nail beds, but leave the nails in perfect shape. Once inside the body, unnoticed for hours, it wreaks havoc on a person’s system.
Recently, I wrote about weak acids, and how the word “weak” doesn’t mean to a chemist what it means to a layperson. To us, saying an acid is weak indicates that it can’t do much damage. To a chemist, a “weak” acid is any acid that doesn’t shed absolutely all of its hydrogen nuclei (otherwise known as single protons) when it’s put in water. Strong acids, like hydrochloric acid, differentiate completely into a hydrogen ion and a chlorine ion. Hydrofluoric acid, meanwhile, keeps its single hydrogen and single fluorine atom together much of the time.
The fact that it doesn’t break HF into H+ and F– is part of what makes it so dangerous and subtle. According to the Encyclopedia of Occupational Health and Safety, “weak acids and bases may readily pass membranes in their non-ionized fat-soluble form while ionized forms are too polar to pass.” Weak acids can hang together, and diffuse through the membranes of human cells. This means the acid can go anywhere in the body, including the bloodstream.
This wouldn’t be ideal under any circumstances, but once inside the body, the hydrogen and fluoride don’t stay together. Calcium and magnesium atoms cause the fluorine to detach, leaving hydrogen ions. Hydrogen ions are the aspect of acid that break apart the proteins in the skin—they’re what “burn” people. Fluorine is also a highly reactive ion and can tear into cells across the body.
Once a cell has been destroyed, it’s dead tissue inside the body, which is always dangerous if it can’t be cleared away quickly. But the acid can cause life-threatening problems even if it doesn’t participate in the wholesale destruction of cells. Fluorine’s affinity for calcium means that bones dissolve and calcium levels around the body drop. Calcium blocks channels in the nerves that otherwise would be clear for sodium, which plays a role in triggering the nerves. At best, this causes numbness. It’s more likely to cause first spasms, then convulsions, and finally heart arrhythmia.
A lack of calcium, if all available calcium is bound to fluorine, causes in influx of potassium—and excessive potassium in the blood. This can disable muscles, starting with the heart. Hyperkalemia causes the heartbeat to become arrhythmic, or the heart to go into fibrillation and stop pumping blood altogether.
Finally, fluorine binds to magnesium. Magnesium also controls heartrate, and a lack of magnesium can cause the heartrate to increase out of control. Basically, hydrofluoric acid in the system not only burns people internally, it cause three different processes that compete with each other to stop a person’s heart.
It would be nice if applying water to dilute the acid would be all it took to make it less dangerous. That’s not the case. Adding water to acid creates a hot explosion of liquid and steam that can spread the acid around further. Most labs keep special neutralizing agents on hand. If people are exposed, there are other agents that are so attractive to fluorine that they will, with luck, convince the acid to attack the agent, not the body. Mostly, though, you just want to stay out of hydrofluoric acid’s way.