Oil painting is regaining popularity as a medium at both the secondary school and college level. Large numbers of students painting with oils at the same time, however, can be very hazardous unless careful precautions are followed.
Oil painting can involve hazards from accidental ingestion of pigments, and from inhalation or skin contact with solvents such as turpentine, turpenoid, or mineral spirits.
Basic Oil Painting
In basic oil painting, students work with tube oil paints and use solvents for thinning the paints, in mediums, and in cleanup. Many pigments are toxic, including those based on lead, cadmium, mercury, chromates, manganese, and cobalt. The main risk is from accidental ingestion of the pigments due to eating while working, nail-biting, pointing your brush with your lips, and similar means of hand-to-mouth contact. Simple precautions and common sense can eliminate the risk. The use of solvents is a more serious hazard. Commonly, a student might have a half cup of solvent in a container, which is normally left uncovered. Over a three-hour class period, about one quarter to half of this might evaporate from the container or by use.
All solvents can cause defatting of the skin and dermatitis from prolonged or repeated exposure. Turpentine can also cause skin allergies and can be absorbed through the skin.
Acute inhalation of high concentrations of turpentine or mineral spirits can cause narcosis (dizziness, nausea, fatigue, loss of coordination, coma, etc.) and respiratory irritation. Chronic inhalation of turpentine can cause kidney damage and possible respiratory allergies. Chronic inhalation of large amounts of mineral spirits could cause brain damage. Odorless mineral spirits or turpenoid, which have had the aromatic hydrocarbons removed, are less hazardous.
Ingestion of either turpentine or mineral spirits can be fatal. In the case of mineral spirits, this is usually due to chemical pneumonia caused by aspiration of the mineral spirits into the lungs after vomiting.
Advanced Oil Painting
In advanced classes, students sometimes mix their own oil paints from powdered pigments. This activity creates the additional hazard of inhaling the powdered pigment. In many colleges, traditional underpainting techniques using turpentine washes are taught. This is very hazardous since it involves brushing onto the canvas as much as a cup or more of turpentine in a short period. Although this is hazardous enough when one individual does a turpentine wash, it become extremely hazardous when a whole class does it due to the enormous amounts of solvent evaporation.
1. Accidental ingestion of pigments can be prevented by not eating, drinking, smoking, or applying makeup while working. In addition, do not point your brushes with your lips. 2. In general, we recommend against mixing your own powdered pigments. If you do mix the powdered pigment, do so inside a glove box or wear a NIOSH-approved toxic dust respirator. A glove box can be made by coating the inside of a normal cardboard box with shellac, covering the top with glass or clear plexiglass, and cutting two armholes in the sides. The pigments can be ground and mixed with oil inside this box.
3. We recommend against the use of the most toxic pigments: lead white or flake white, the arsenic variety of cobalt violet, true vermillion (mercuric sulfide), and chrome yellow (lead chromate). 4. For solvents, we recommend using odorless paint thinner or turpenoid rather than the more toxic turpentine. 5. The amount of ventilation needed depends on the amount of solvent that evaporates. Assuming that a class is doing basic oil painting (and not turpentine washes), teachers estimate that each student has a container with about half a cup (4 ounces) of solvent. Assuming that only one quarter evaporates during a three-hour period, the amount of dilution ventilation needed per student is about 100 cubic feet per minute (cfm). For a class of 20 students doing oil painting, the amount of dilution ventilation needed would be 2000 cfm. This ventilation rate is based on the formula: (DV) x (# pints evap'd) x (K) / (# minutes) where DV means the dilution volume for that solvent per pint of solvent evaporated, and K is the safety factor. In the above example, the dilution volume for mineral spirits is 30,000 cubic feet/pint, and a safety factor of 10 is used. (The calculation method is found in Chapter 6 of CSA's book, Ventilation.)
6. For an advanced class doing turpentine washes, the amount of ventilation needed is much greater. Assuming each student uses half a cup (4 ounces) of turpentine for a wash - all of which evaporates, and assuming that this wash is done in the first hour of the class, then the amount of additional dilution ventilation needed is 1,050 cfm extra per student. This amounts to a total of 1150 cfm per student, and 23,000 cfm for a class of 20 students. (This uses a dilution volume of 25,500 cf/pt. for turpentine.) This amount of ventilation is impractical and we recommend against doing underpainting using turpentine washes. Acrylic underpainting is suggested instead. 7. Makeup air to replace the air exhausted should enter the room in several locations along the ceiling, and be exhausted at floor level to maximize the distribution of air since the vertical paintings restrict flow of air.
8. Evaporation of solvent can be further reduced by: • covering all open containers of solvent with aluminum foil wrapped around the brushes and top of container. • placing waste solvent in approved solvent waste cans and closing all containers of waste solvents when not being used. • reducing class size or the number of students painting with oils. 9. Note that once a dilution ventilation rate is fixed for these painting classrooms, that fixes the total amount of solvent that can be evaporated in a class. Work rules would have to be established to ensure this is followed. 10. Oil painting classrooms should have an eyewash fountain in case of solvent splashes in the eye.