While working on a construction site years ago, I heard a shout and walked over to learn that one of the carpenters had put a nail through his hand from an air-powered nail gun.
We drove him to the emergency room, and before long, he was back on the job. The projectile had missed all the critical parts. As the expression goes, “Hands are the moneymakers,” so he was pretty lucky.
Anybody with common sense can recognize and seek treatment for a nail-gun injury. But something that everyday smarts can't handle is injury from a leak of high-pressure fluid injected deep into flesh.
I've written about big leaks from chemical plants and refineries that cause burns and fireballs, but this is about leaks from the other end of the size spectrum: nearly microscopic pinholes less than half a millimeter – a few thousandths of an inch – across.
A leak from such a tiny hole doesn't sound like much to worry about, and it isn't when little pressure is behind it, like a leak in a garden hose. But at common hydraulic-system pressures, everything changes. High-pressure fluid from a pinhole emerges at hundreds of miles per hour. While that speed drops rapidly with distance, at close range, such a jet can be devastating. Permanent injury is very possible without rapid and expert treatment. It's another hazard from what I call the Machine Frontier.
The first machines that relied on hydraulic actuators date back to English engineer Joseph Bramah, who recognized and exploited the enormous potential of Pascal's Law. That principle says that since fluids like water can't be compressed, pushing on fluid at one end of a closed circuit will make a ram move at the other end. More pressure means more force.
While Bramah patented his hydraulic metal-forming press in 1795, broader adoption of this breakthrough was slow because it required greater precision and higher-quality materials. Maybe that's a good thing, since this boon had a bane. German doctors first read about a high-pressure injury in 1925, followed in 1937 by an American Medical Association report about a mechanic injured by a 4,000-psi jet of fuel from a diesel engine injector.
Thanks to wartime advances in materials science, high-pressure applications grew rapidly in the 1950s, such as the substitution of hydraulic cylinders to replace cable-drawn bulldozer blades.
Hydraulic systems are so compact, robust, and powerful that I predict their shiny cylinders will be widely used 100 years from now.
Hydraulic pressures today range upward from what's common in farm and construction equipment, around 2,500 pounds per square inch. New airliners and the V-22 Osprey rely on 5,000 psi hydraulics because shifting to a higher pressure allows designers to save weight on hoses and fittings. Some industrial systems go far beyond that, hitting 30,000 psi and even five times that.
High-pressure injection (HPI) wounds happen in all kinds of places, not just in factories and repair shops. They can happen at home, at a construction site, or on a farm.
HPI injuries are rare (less than 1% of hand accidents), but that rarity means the first line of doctors and nurses may not know that they're facing a real emergency and time is critical.
Here's an illustration of how important timing is for HPI diagnosis and treatment. A sugar-beet farmer working at night sees a mist coming from near the bundle of hoses emerging from the hydraulic pump on his idling tractor. He picks up a flashlight to investigate, and seconds later, feels a sting on the back of his hand. It's like a poke from a sharp wire. Glove off, he sees only a slightly reddened and tender patch of skin. He's suffered many cuts and bruises over the years, so this doesn't seem like a priority, not when the family beet fields are finally dry enough for harvesters and trucks.
What the farmer doesn't know is that what felt like a sting came from a pinhole leak in a 2,500-psi hydraulic hose. That seemingly innocuous whisp started as a 400-mph jet. At touching distance, his glove couldn't stop the jet from injecting his hand with toxic fluid.
By dawn, his hand is stiff as a board, and his forearm feels like it's on fire. It's off to the hospital. Now the injury's reached the six-hour point, and the question is whether the medical team recognizes the seriousness and knows what to do, or fails to act in time. As each hour passes without treatment, the odds of amputation go up.
What happened to Pennsylvania dentist Ralph Ginter is a reminder that hobby farmers and garage-scale hobbyists are at risk, too. Ginter accidentally injected his index finger with hydraulic fluid from his tractor. He consulted a surgeon but ended up waiting 24 hours for a referral to the appropriate surgical treatment. Ginter sued the first doctor on the grounds that the delay caused so much trauma to his index finger that he lost use of it, along with his medical practice.
Ginter's case is a warning to anyone using high-pressure gear that treatment of a severe HPI injury needs more than common sense. Massaging the wound site to “push out the foreign liquid” just spreads it further. Antibiotics alone won't solve the problem because an HPI with a toxic fluid – especially a solvent or oilbased paint – requires complete removal. So treatment is likely to need medical imaging followed by expert invasive surgery to lay open and clean out the part of the hand or arm that is affected, called debridement. This may require multiple surgeries to remove dying or infected tissue, even amputation. The photographs are scary … take my word for it.
Why is HPI so damaging? The fluid jet penetrates the skin at near-bullet-like speed, then dissipates that energy in tissue and deflects when it hits an obstruction such as a bone or sheath. The fluid spreads out to cause more damage, following lines of least resistance. While every case is unique – highly dependent on the exact circumstances of the accident – HPI can cut off blood circulation to confined areas, causing a serious complication called “compartment syndrome.” Untreated infections lead to gangrene.
Because full recovery from HPI is not guaranteed, the best approaches are to avoid the injury entirely, and to be prepared when it happens.
Prevention: When a hydraulic system is energized, it's tempting to reach out and check a leak that looks like a misty cloud. Instead, use a piece of cardboard or wood at the end of a stick. Unfortunately, it's not easy to find pinhole leaks when hydraulics are safely depressurized. A pinhole will look more like a speck of dirt than the looming hazard it is. Oily spots or aging hose sheaths may provide the only clues.
Preparation: Given the large number of people who may come into contact with hydraulic systems, I've focused on hydraulic-fluid injections in particular. But the same cautions apply to anyone at risk of high-pressure fluid leaks: get the patient and situational info to a hospital right away. Hospitals need to know what they're dealing with: patients have arrived with injections of wax, grease, power-washer water, plastic, fuel, petroleum jelly, air, paint, solvents, and even cement.
Some forward-thinking companies like Parker Hannifin provide wallet cards for at-risk workers, so that emergency rooms will be clear on the equipment, fluids, and pressures involved.
Tiny leaks can signal bigger problems out of sight. In 1999, staff at the Tosco Avon refinery in Martinez, California, didn't take a pinhole leak in a naphtha line seriously enough to stop work and deal with serious corrosion in pipes and valves feeding a “fractionator” unit that processed crude oil. The corrosive material – water and ammonium chloride – had been spilling from an overloaded desalter upstream.
Because of the balky valves, maintainers who started working on the system two weeks later weren't able to drain all the naphtha before cutting into pipes. The hot fractionator ignited the flammable cloud, killing four men trapped on high scaffolding.
Over several years, a tiny drip of borated water from a cracked nozzle at the Davis-Besse Nuclear Power Station in Oak Harbor, Ohio, caused an accumulation of boric acid that ate all the way through the unit's six-inch-thick pressure vessel dome. By the time of discovery, the reactor was protected by only a membrane of stainless steel.
In 1973, economist E.F. Schumacher published a book called “Small is Beautiful.” Now imagine a book that won't ever be a bestseller but features a topic that's worth remembering: when it comes to pressurized pinhole leaks, “Small Can be Sneaky and Dangerous.”