Safe Handling: Flammables, Corrosives, and Toxics

Safe handling of hazardous chemicals means using the smallest necessary amount, appropriate protection and the right equipment for the type of hazard: flammables are kept away from ignition sources, corrosives are handled with splash protection, and toxic substances are used in a fume hood. In brief: never heat flammable liquids over an open flame, always add acid to water and never water to acid, and never smell or taste an unknown chemical.

Flammable, corrosive and toxic chemicals are common in school and university laboratories, and each type of hazard needs its own precautions. This article explains how to work with each type, includes the key figures such as flash points, compares the hazards in a table, works through a dilution problem with the correct procedure and gives examples of lessons learned from the history of laboratory accidents.

How do you handle flammable chemicals?

A flammable liquid gives off vapor that can ignite. The flash point is the lowest temperature at which a liquid gives off enough vapor to form an ignitable mixture with air. The lower the flash point, the greater the danger: diethyl ether has a flash point of about −45 °C and acetone about −20 °C, so both can ignite at room temperature, while ethanol has a flash point of about 13 °C. Vapors are usually heavier than air, so they can travel along a bench or the floor to a distant source of ignition.

• Keep flammables away from flames, hot plates, sparks and electrical equipment that may spark.
• Use the smallest quantity needed. Keep bottles closed when not in use.
• Heat with an electric heating mantle, hot plate or a water bath, not with a flame, and never heat a closed container.
• Work in a ventilated area or fume hood, and do not pour flammable liquids down the drain.
• Keep a fire extinguisher and fire blanket within reach.

How do you handle corrosive chemicals?

Corrosives, which include strong acids (hydrochloric, sulfuric, nitric) and strong bases (sodium hydroxide, potassium hydroxide), destroy living tissue and some materials. Bases are especially insidious, since they may not hurt at first and can cause deep damage.

• Wear chemical splash goggles, gloves and a lab coat. A face shield is added when working with larger volumes or concentrated solutions.
• Pour slowly, and hold the container low so that splashes are minimal.
• When diluting, always add acid to water, never the reverse. Adding water to concentrated sulfuric acid can release so much heat locally that the water boils and splatters acid.
• Use carriers when transporting bottles, and do not hold a bottle by its neck.
• If skin contact occurs, rinse immediately with water for at least 15 minutes.
• Neutralize small spills as directed by the instructor, using the appropriate neutralizer such as sodium bicarbonate for acids.

How do you handle toxic chemicals?

Toxic chemicals can harm the body through inhalation, skin absorption, ingestion or injection. Some effects appear immediately, and others, such as cancer, develop after repeated exposure over years. Safety is based on the principle of keeping exposure as low as reasonably achievable.

• Use a fume hood for volatile or powdered toxic substances, and keep the sash at the marked height.
• Choose gloves that are resistant to the specific chemical. Check the glove chart.
• Never pipette by mouth. Use a pipette filler.
• Avoid creating dust or aerosols. Weigh powders in an enclosure where possible.
• Handle mercury, heavy metals and organic solvents according to institutional rules, and clean spills with the proper kit. Never sweep mercury with a broom.
• Wash your hands after handling any chemicals.

Hazard comparison

What general rules apply to all hazardous chemicals?

• Read the label and safety data sheet before use.
• Do not transfer chemicals into unlabeled containers.
• Never return unused chemicals to the stock bottle, as this may contaminate it.
• Keep incompatible chemicals apart: oxidizers away from flammables, acids away from bases and cyanides.
• Know the emergency procedures before you begin.

Worked example: diluting concentrated acid

A student must prepare 500 mL of 1.0 mol/L sulfuric acid from a concentrated stock that is 18 mol/L.

1. Volume of stock needed. Use C₁V₁ = C₂V₂. V₁ = (1.0 × 500) ÷ 18 = 27.8 mL.
2. Prepare water. Place about 300 mL of distilled water in a 500 mL volumetric flask or a beaker, which is more than half full, with the flask in a tray.
3. Add acid slowly. Using a pipette or a measuring cylinder, add 27.8 mL of the stock acid slowly to the water with gentle swirling. The mixture will become hot.
4. Cool and fill. Allow the solution to cool to room temperature, then add distilled water to the 500 mL mark and mix well.
5. Label. Write the name, concentration, date and your initials on the bottle.

The acid is added to the water, since the larger amount of water absorbs the heat released and keeps the temperature rise safe.

What has history taught us?

Accidents have shaped modern laboratory practice. Fires from flammable solvents led to the standard use of flammable storage cabinets and the rule against open flames near solvents. Serious injuries from pipetting by mouth made pipette fillers standard equipment. Investigations by safety organizations, such as the U.S. Chemical Safety Board, publish lessons from accidents in laboratories and industry, which are used for teaching and for improving regulations.

Which mistakes are common?

Mistake 1: Adding water to concentrated acid

Always add acid to water. Remember: “Do as you oughta, add acid to water.”

Mistake 2: Heating a flammable solvent with a Bunsen burner

Use a water bath or electric heater, and no flames in the area.

Mistake 3: Smelling chemicals directly

Waft the vapor gently toward your nose only if the procedure allows it.

Mistake 4: Ignoring the incompatibility of waste or storage

Mixing incompatible chemicals can create toxic gases or fires. Keep them separate.