There are advantages to using volatile solvents in decorative coloring agents like dyes: They spray well and dry immediately, very controlled work can be achieved, they don't puddle and run, you can apply multiple coats very quickly, and they produce a “soft touch” effect. They are also very forgiving—you can over-apply and still get good results. But there are problems too—they are very dangerous. Over the past couple years, worker injuries, death, and destruction to property have resulted. You can also use dyes with water, but their application is more limited, so contractors tend to use solvent products. Solvents in stripping agents for removing paint and sealers can also cause safety issues.

My own experience

If you must use solvents, ensure that all points of ignition are turned off before beginning work.
If you must use solvents, ensure that all points of ignition are turned off before beginning work.

As a result of my own painful, personal experience I am writing this article to warn you about the dangers inherent in working with solvents and to make suggestions about precautions and safety.

Several years ago I volunteered to help a friend dye-color his walkout basement floor. He masked the walls for me and got things ready. I arrived late in the day, was tired, and didn't perform my normal check list. He masked the wall with paper, so I didn't notice a small door leading to a water heater. I mixed acetone solvent and dye together and sprayed the first application. When the application was about 2/3 dry I started the next coating. After a few seconds there was an explosion, and after my initial shock I saw flames everywhere —including on me. I was hit with a momentary 1800° F flash of air. I ran out the door and jumped in their swimming pool. The flames were quickly put out, and there was minimal damage to the house. But I still carry significant burn scars from the event. I was told afterwards I was lucky I didn't breathe in any of the hot air from the flames—when this happens it's usually fatal.

What you need to know about solvents

Some solvents are more dangerous than others in causing fires or explosions because they ignite at low temperatures, are heavier than air, and some evaporate much more quickly than others. The information you need to know can be found on the Material Safety Data Sheets (MSDS) for the solvent you are using, but there are a few definitions you should understand first. Here's how to determine how much risk is associated with the solvent you are working with.

Flash point. In their liquid state, flammable liquids won't burn. It's only when their vapors mix with air in certain percentages that a dangerous situation develops. Flash point is defined as the temperature at which a liquid will give off enough flammable vapors to ignite when it is exposed to a flame or spark. The lower the flash point, the easier it is for a solvent to ignite, and the more dangerous it is. A flame must be present for ignition to occur. For example, the flashpoint of acetone is -4º F, meaning that at this temperature enough evaporation of the solvent occurs to provide conditions for an explosion. (Fire point is the temperature where ignition occurs spontaneously without a flame.)

Vapor density. Vapor density is the weight of a vapor or gas compared with that of water—which is always 1.0. If a solvent has a vapor density higher than water, it means that it is heavier than air and will tend to congregate in low places. These solvents are potentially more dangerous in confined areas than are solvents that are lighter than air. The vapor density of acetone is 2.0, so it is heavier than air and concentrates near the floor in a state that can easily cause an explosion.

Explosion limits. Two numbers are reported for the explosive limits of a solvent; the lower explosive limit (LEL) and the upper explosive limit (UEL). The range between LEL and UEL is the climate in which fires and explosions occur if an ignition source is present. So the greater the range between the LEL and the UEL, the greater the chance for an explosion. Below and above these limits doesn't cause problems. Using acetone as an example, its LEL is 2.6% and its UEL is 12.8%, meaning that its explosive limit is greatest when the concentration of solvent in the air is between 2.6% and 12.8%.

Taking precautions

Read the MSDS information about the solvent you intend to use before you do anything else, and consider the jobsite conditions. Look up the flash point, vapor density, and explosion limits for the solvent to understand the risks better. Here are some other tips:

  • With any solvent except water, make it part of your routine to check your work location for any source of ignition. Turn off pilot lights, electric motors, and anything that could create a spark. Work out your own checklist and go through it for every installation.
  • Factor in the risk that ambient conditions can add. Hot, dry air, for example, increases the risk for any solvent.
  • Wear protective clothing. Cotton or natural fiber long-sleeved shirts and long pants are best—cover your body.
  • Think about temporary lighting and extension cords. Knocking over a light or tripping on an extension, pulling it out of an outlet, can cause sparks.
  • Start your work with an escape route in mind should you need it.
  • Be sure there is good ventilation, but don't use a fan that can cause a spark.
  • Adding water to acetone and alcohol solvents can work well and reduce the amount of solvent—less solvent, less risk.
  • Some solvents soften the hoses on sprayers causing leaks that can spray solvent on your clothing, on light bulbs, or other risky places. Choose sprayers that are resistant to the solvent you are using.
  • Vapors can travel beyond your work area. Consider adjoining spaces and the possibilities for ignition there.

—Mike Miller is the owner of “the concretist” (which dictionaries define as “one who practices poetry on concrete”). He installs chemical stain, overlay cement, and other artistic finishes all over the United States. His company is located in Benicia, Calif.