People go a little crazy about safety, in both directions. Some artists eschew all protection, relying on the fact that bad things only happen to other people. Other people bury them selves under protective gear, and go to work looking like they're on a Superfund cleanup crew.
Everyone does stupid things regularly, no matter how much experience they have. The amazing thing about workplace injuries is that practically everyone who gets hurt will freely admit later that they not only knew they were doing something stupid, but in fact were actually thinking about how stupid it was at the time of the accident. How much effort you want to put into safety is a personal choice, but the important thing to remember is that our intuition about how quickly slight risks add up is not good: we see that the the chance of getting hurt on any one occasion is very small, but forget that we're going to take that chance thousands of times.
Therefore, workplace safety has two parts: first, don't rely on your own good sense alone--you have to make safe practices something you do automatically without thinkng, like washing your hands in the bathroom. Second, be mindful--pay attention to that little voice telling you that you are doing something stupid.
If you are employing studio helpers, or allowing people to use your studio, safety is doubly important because of liability. Be sure you know what OSHA has to say about the equipment and processes you use if anyone other than you is involved. This goes double for young people in the studio. A lot of safety is using good sense, which mostly comes from experience, something that the young do not usually have a lot of. Don't assume people new to the studio understand basics--spell it out in detail.
A respirator is highly advisable when working with marble and limestone, and absolutely essential when working with most other varieties of stone. Carving, particularly with power tools, generates clouds fine dust that lingers in the air. Even if you wear a mask, ventilation is important too. Fine particles settle in still air at a rate of about a foot an hour in still air, so in an unventilated studio, the finest, dust can still be in the air the next day.
Disposable paper "nuisance dust" masks, the kind with the rubber band, and the metal strip that pinches over the nose, are worthless, and do almost nothing other than giving you a false sense of protection. When you take one off, you can see thick white streaks around your nose where the air pours in around the edges of the mask. The thick fiber ones are better, but still pretty poor. For marble and limestone, respirators should be rubber or metal, with a soft rubber rim so it seals to your face, and replaceable cotton filters. Do not get the ones with the screw-in canisters, which are for chemicals and fumes, not dust.
The mask should pass the pressure test: seal the filters with Saran wrap and a rubber band, and inhale. There should be a vacuum against your face when you try to suck air. If there isn't, the mask isn't doing much. Note, sealing the filter with the palm of your hand is is not as good a test, because you are squeezing it to your face more tightly than it would be in actual use. Replace the filters when it becomes noticeably harder to draw air through them.
A variety of filter types are available. For nuisance dust, like marble, you only need cotton unless you're extra sensitive. "HEPA" is the highest level of filtration. HEPA filters are more expensive, and although the higher level of filtration will not hurt, they are not considered necessary for carving marble, limestone, which are chemically more or less the same as chalk. HEPA filters usually have layers of pre-filters in front of the HEPA-rated layer, to reduce unnecessary loading of the HEPA layer. Both layers have to be changed periodically.
If you are really fastidious, there are supplied-air masks that maintain positive air pressure inside the mask, eliminating all leakage, as well as the need for a perfect seal to the face. Clean air is continuously blown into the mask though a hose, so they don't depend on you sucking air through a filter, and unlike a regular mask, the intake is not right in front of the dust source, so the filters are only filtering air that is already relatively clean. The masks that have one big plastic cover over your face are great--they don't encumber you, because they don't clamp onto your face, and the face shield obviates the need for glasses. Also, many kinds of masks direct your breath onto your face, which tends to fog your glasses, and these don't do that. The filtration unit and blower can be on a belt-pack, or in a stationary unit that can be some distance away and supply multiple masks. The masks can be either full-face or just cover the mouth and nose. The down side is that they are very expensive--the full systems are in the $200 range for one person, and $1000 range for a multi user unit.
Marble and limestone are almost pure calcium carbonate, the same substance as chalk, which is classified as non-toxic. You can eat the dust and breathe it without poisoning yourself, but it will still make your lungs ache. Granite and other hard-stone dust is not harmless--it's rich in silica and similar substances, and working it dry produces copious, finely powdered glassy dust. Sandstone, being composed mostly of silica sand, also produces silica dust. Chronic exposure to fine silica dust causes silicosis, a very serious, chronic, degenerative, and incurable lung disease. It's not a good idea to carve silica-containing stones in a residence regardless of your ventilation system. If you do carve granite, or other stone containing silica or other glassy substnces, leave your work clothes in the studio to avoid bringing the dust home. Keep them separate and wash them all at once. Silica is harmless when it's wet and harmless to wash down the drain (powered silica is produced in nature by waves or running water causing gravel and stones to rub together.)
Other stone dusts can be irritating too. Talc, from soapstone, can be also be irritating in large concentrations, similarly to lime dusts, and requires similar protective measures.
Asbestos is a different order of hazard than the other stone dusts and should be avoided absolutely, for a number of reasons. In addition to causing asbestosis, a lung-scarring condition similar to silicosis, asbestos is also carcinogenic. Moreover, the dust can be exceedingly fine, far below the one-micron level, and not even HEPA filters get it all. Some varieties of soapstone, serpentine, and other commonly carved stones contain asbestos, so use them only if they come from quarries that guarantee the stone is asbestos free, or have it analyzed if you don't know where it comes from. (Asbestos is one of the serpentine mineral group, and is chemically identical to harmless varieties of serpentine, differing only in crystal structure.) Stone you buy at a sculpture supply house is usually ok--this caution applies more to stone you collect yourself, recover from abandoned quarries, etc. The "green" in green marble is usually serpentine, and should be treated as suspect. If in doubt, grind a little dust and have it tested--asbestos analysis is easily available, due to the increasingly strict laws on asbestos abatement. Not only is stone containing asbestos impossible to carve safely in a studio environment, there are serious legal implications: by law, asbestos is a hazardous waste, so even cleaning it up requires a license, special equipment, and a certified hazardous waste landfill.
Be aware also that in some regions, there are stones that contain chemically poisonous metal ores such as lead, arsenic, cadmium, uranium, chromium, so if you intend to carve stone you have collected yourself, you should find out what it is first.
If you're a smoker, be fastidious about dust inhalation. Smoking multiplies the effect of lung irritants, because tobacco smoke temporarily suppresses the ability of the lungs to clear themselves. It's not just smoking while you are in the dusty studio--smoking at all is a problem, because the effect persists for several hours after smoking.
See the section on air cleaning.
Event the best masks aren't perfect; the workplace should be kept clean and ventilated. If you are using power tools, the dust will be beyond the level where you can just put a fan in the window. A variety of dust collectors and ventilation options are available.
Portable dust collectors are big stationary vacuum cleaners with large-diameter hoses to put the collection head right at the work. The draw large volumes of air and do a good job of sucking up most of the dust at the source. Standard filter bags for collectors get dust down to one micron. These are fantastic if you can afford it.
Ambient air cleaners hang from the ceiling, and filter the room air. A typical studio-sized model cycles a volume of air the size of an average room every five minutes, through a one-micron filter. This is pretty good, but it doesn't mean the air is clean again five minutes after you stop grinding. It's more like a fish-tank filter, because the cleaned air is continuously dumped back in with the dirty air.
The ideal situation is to use both--a dust collector at the source and an air cleaner running to scrub the room air. If you can afford only one or the other, choose the stationary vacuum, because it cleans the air to a level where you can put a fan in the window and not blow out clouds of dust.
For table-top sized work, downdraft tables are excellent. These are workbenches that suck air away from you through perforations in the tabletop, directly into an air filter.
Note that a one micron (abbreviated µ), a thousandth of a millimeter, is actually only a moderately fine filter. A micron is much larger than the particle size trapped by the HEPA filters, which are rated to collect 99.97% of airborne dust down to 0.03 microns. The difference betwee 1.0 micron and 0.03 is the size difference between a grape and a beach ball.
You often find yourself spontaneously picking up a tool to do some little thing you just noticed. It's tempting to do the little task without putting on the glasses, and 99.9% of the time nothing will happen, but the little chances add up. Take two seconds and put on the safety glasses.
Chips of stone aren't the only thing that can fly around the studio. Steel tools can throw chips or sparks occasionally, even when carving soft stone. The chips can come from either end of the tool.
Disintegrating tool tips, cutting and grinding wheels, and wire-wheels can throw metal much harder than a chisel can throw stone, and they are less predictable.
Grinding stones can break up from centrifugal force. Metal burrs can break, or slip loose. If they do come loose, they don't necessarily just drop out spinning. The side pressure can cause them to come out crookedly, in which case the shaft can act like a throwing arm, slinging it very hard. Don't run die grinding tools in a power drill--drill chucks are not designed for vibrating bits and pressure from the side, and are particularly likely to sling the departing bit because they have jaws the bit can get between. The collet on a grinder is much less likely to sling a bit than a chuck.
Gloves protect you from scuffs and blisters, and they are some protection against getting cut, but they don't protect you from crush injuries, which are the biggest danger to hands. It's not just the hammer. You can crush fingers, hands, or feet anytime you are moving stone, by being pinched between two stones, or between a stone and the bench, wall, or floor, or by getting caught by winches, lifts, etc.
You always want to wear boots around stone, preferably boots with steel-toes. Steel toed boots give a lot of protection from moderate impacts and pinches, but they have limits. They mostly protect your toes, and only up to a point, but they are definitely a good thing.
The only real protection for the hands is to be alert, think, and take care when moving stone or metal. The most important thing is not to try brute force to move stones that are too heavy or unwieldy to fully control. A good rule of thumb is, if you even have to think about whether you're strong enough to do something, then you can easily get hurt doing it, not just from strain, but because you may not be able to maintain control. If it's too heavy, get help or use mechanical equipment.
It's not just dropping a stone; anytime a stone is in motion, it's dangerous. One common way to get pinched is when moving a block into a tight place, with a hand truck. You try to hold it back when setting it down, and get your hand pinched between the stone and the wall, or another stone. Don't use your hand here--use a piece of 2x4 at an angle to control it. Or set it down a foot away, then use a crowbar to inch it into place. Another very common way to get pinched is when walking a stone by rocking and twisting at the same time. You misjudge, and your hand gets slammed between the stone and the wall.
It's easy to armor your work gloves in this critical spot. Cut several one-and-a-half inch strips from the bottom corner of a round Tupperware container as shown in Figure *. Leave half an inch of plastic on each side of the ridge. Two or three of these stacked up and duct-taped to the top of your glove over the knuckle will completely dissipate the force of a normal hammer strike. Wrap the duct tape all the way around the palm a couple of times. The tape will make the glove last longer, too. Do the wrapping with your hand almost closed in a fist, or it will be too tight.
The use of vibrating tools can lead to a nasty condition known variously as "white fingers", "Vibration-Induced White Finger" (VWF), "dead fingers", and "dead hand." All these gruesome terms are synonyms for Occupationally Induced Reynaud's Syndrome, which is characterized by cold, bloodless, blanched-looking fingers, accompanied by numbness and tingling of the digits. Medically, it's closely related to the response of your fingers to cold, and in fact, in some people, cold is enough to trigger Reynaud's syndrome. Early stages of this condition are characterized by numbness and/or tingling that persists for more than an hour or so after stopping work with the offending tool. If the condition appears, don't just tough it out--it is important to stop using vibrating tools, because the symptoms progress rapidly on continued exposure, and can lead to severe problems. The condition is strongly affected by temperature, and individual susceptibility varies widely. Vibrating tools can also cause a number of more diffuse complaints known collectively as "vibration syndrome." Muscle weakness, pain in the shoulders and arms, as well as headache and depression have been linked to chronic exposure to vibration.
Susceptibility to vibration injuries is the luck of the draw--some people get them and some don't, for no obvious reason; being tough in other ways doesn't really affect succeptibility. If any of these symptoms appear, get the advice of doctor who is knowledgeable in the field of occupational health.
The big hazards with bench grinders are flying debris, either from the workpiece or from the stone itself. This is particularly true if the rotational speed limits for the wheel are exceeded. The maximum speed for the wheel should be printed on it.
Store stones carefully, and don't let them bang into each other, or come in contact with concrete floors, etc. Anytime you change stones, check the stone visually for cracks, chips, and flaws, and do the tap-test, i.e., tap it lightly with something hard and listen for the tone. You can hear a crack in a grind stone, just as you can hear a cracked bowl or plate in the kichen. If the grind stone has a crack, not only should you not use it, you should break it up with a hammer so that it cannot be rescued from the trash. (The pieces can be useful for sharpening and other hand grinding.)
Stone wheels throw most sparks pretty predictably, so it is tempting to skip the safety glasses. Do so at your peril-they sparks don't always go straight, and they can bounce. They're glowing because they are on fire. You can often see tiny craters melted into your safety glasses after you have used the wheel for a while. They also go aound corners--regular glasses are better than nothing, but they aren't good enough--stuff still bounces in from the sides. The wires break off of wire wheels all the time, and they can get thrown hard enough to stick in your skin, let alone an eye.
Angle grinders present all the hazards that bench grinders have, but with the additional possibility of winding your clothing into it, or bouncing it off the work and into yourself.
Clothing gets wound into them in a flash, and they can pull you in more powerfully than you can stop with your arm strength. Tuck everything in--hair, sleeves, etc., and don't wear jewelery, bandanas, etc. It's important to use them only when standing in a stable, comfortable position.
As with all power tools, click the trigger before plugging it in even if you are not holding it, to be sure that the trigger lock is not on.
Carving can be hard on the skin. Marble dust is alkaline, and extremely absorbant, and leaches the oil from the skin, pruning your skin, leaving your fingertips chronically looking like you just washed the dishes. It won't kill you, but expecially when combined with cold weather, it can lead to painful cracking that is slow to heal. Rinse the dust off your hands and apply lotion frequently. Vaseline Intensive Care is particularly good, because it leaves a waxy film. If you are particularly sensitive, use a liquid-gloves barrier cream.
Air seems like a benign substance, but compressed, it is nothing to fool around with-never let kids near it, and be sure anyone working in your studio knows what they are doing. A large proportion of commpressed air injuries are caused by practical jokes, and innocent fooling around.
Putting the air squirter in, or even close to, your mouth or other body orifice, can easily cause a fatal injury. Your body is only built to deal with pressure of a pound or two of air pressure. You can perforate a lung just blowing up balloons-a compressed air line has a hundred times as much pressure.
Another common source of accidents is playing around with it by shooting things out of tubes, etc., using a blower handle.
The compressor itself can be a dangerous object, expecially if the drive belts and wheels are not fully covered, expecially because compressors turn themselves off and on automatically in response to tank pressure. Slow leaks can cause them to go on at any random moment. If you are going to work on it, unplug it--don't just turn it off.
Also, the energy of compression heats the air, making the compressor head extremely hot. The air intake (the small round hole in on the side of the air filter, on the extreme top left of the compressor shown) has high negative pressure, and will raise a bruise on your skin should you accidentally touch it when the compressor is on. It would produce a very serious injury if a more delicate part of the body, such as an eye or ear, came close to it.
A lot of air tools are extremely loud, expecially the carving handles. You get used to it quickly, but it doesn't have to be alarmingly loud to be damaging, and air hammers get used for hours at a time. Seriously, use your ear protection when using air.
The other big hearing hazard is using a blower handle to squirt air on yourself to dust off. It is a very common practice, but it is considerably more dangerous than it looks--OSHA and industrial safety people warn against it. Still, most people in shops with compressed air routinely use it for this. If you do, beware that you can blow out an ear drum very easily, and it can drive particles into the eyes even at a distance. Both of these are common industrial and shop accidents. Be particularly careful blowing near waste from metal working tools such as drills and hacksaws, because the metal particles are dense and sharp, and hit with more force than stone dust.
Many air tools have powerful exhaust streams that produce the same kinds of hazards as manual blowers. It is a common practice to turn these tools backwards, and use the waste air to dust off the workpiece. If you do this, use appropriate caution--it's still a high-speed air stream.
No power tool should be used when sitting--terrible things happen when they fall into your lap. They should never be used when you're in an awkward or uncomfortable position. Don't use anything more demanding than an electric drill on a ladder. If you have to use the heavy artillery up high, set up a proper scaffold.
A very common mishap is winding the clothes or hair into a drill, drill press, or angle grinder. It's amazingly easy to do and it's very sudden. Everything should be tucked in and secured, and never wear a necktie, bandana or necklace when operating any power tool.
Unplug the air or electric line when you change tools, and get in the habit of clicking the switch to disengage the lock-on button before plugging in any power tool. For stationary tools, unplug them before doing any work, including changing cutters. Don't use any damaged tool tip or wheel even if it seems to still work fine. If it cracked or chipped, it can easily crack further, and it's probably unbalanced as well.
That simultaneous use of beer and tools is widely recognized to be a bad idea.