Laboratory safety rules exist because every prohibition on the list traces back to a real accident. Whether you’re filling out a lab safety worksheet for a class or reviewing protocols before working in a research facility, the “don’ts” of laboratory work fall into clear categories: what you can’t eat, touch, mix, store, wear, or dispose of improperly. Here’s a thorough breakdown of each.
No Eating, Drinking, or Personal Care in the Lab
This is the most universal rule in any laboratory. Eating, drinking, smoking, chewing gum, applying cosmetics, and taking medicine are all strictly prohibited in any space where hazardous chemicals are used or stored. The NIH extends this to include handling contact lenses, since touching your eyes with potentially contaminated fingers creates a direct route for chemicals or biological agents into your body.
The reason goes beyond “you might spill something in your coffee.” Contamination happens through multiple invisible pathways: residue on gloves transfers to food when you reach for a snack, airborne chemical particles settle onto open containers and utensils, and placing a water bottle on a bench surface that was wiped down with a solvent means you’re now drinking from a contaminated container. You can’t see, smell, or taste many of the substances used in labs, so the only safe policy is a complete ban.
This also means food, beverages, cups, and eating utensils cannot be stored anywhere in the lab. Laboratory refrigerators, freezers, ice chests, cold rooms, and ovens are off-limits for food storage or preparation, even if they look clean.
No Mouth Pipetting
Pipetting by mouth is banned in every modern laboratory. Mechanical pipetting devices exist for exactly this reason. Mouth pipetting risks direct ingestion of chemicals, biological cultures, or radioactive materials. It also introduces saliva into samples, contaminating the work. This one appears on nearly every lab safety worksheet because it’s one of the oldest and most dangerous habits in science, and it took decades of regulation to fully eliminate it.
No Unauthorized Experiments or Working Alone
Running experiments that aren’t part of an approved protocol is prohibited. This includes modifying procedures without approval, skipping steps to save time, or “just trying something” outside of your assignment. Every experiment in a properly run lab has been reviewed for hazards, and deviating from standard operating procedures removes that safety net.
Working alone in a laboratory is also explicitly prohibited by OSHA guidelines. If you’re exposed to a chemical, cut by broken glass, or lose consciousness from fume inhalation, there’s no one to help you or call for emergency response. Labs require a buddy system or, at minimum, someone who knows you’re there and can check on you.
Never Add Water to Acid
When diluting acids, you always add acid to water, never the reverse. The memory aid is “do as you oughta, add acid to water.” When water is poured into concentrated acid, it floats on top of the denser acid layer. The extreme heat generated by the reaction causes the solution to boil violently, projecting hot acid out of the container and onto you. Adding acid slowly to a larger volume of water disperses that heat safely.
Chemical Storage and Mixing Mistakes
Incompatible chemicals stored or mixed together can produce toxic gases, fires, or explosions. A few examples that commonly appear on safety worksheets:
- Acids and bases together (like hydrochloric acid and ammonium hydroxide) generate extreme heat, enough to boil over a container.
- Acids and bleach, cyanides, or sulfides release toxic fumes. Mixing acid with cyanide produces hydrogen cyanide gas, which is lethal.
- Nitric acid and any organic material (ethanol, acetic acid, oil) can ignite or generate dangerous heat, even when the acid is dilute.
- Perchloric acid and wood or paper can form a compound that spontaneously catches fire.
- Silver nitrate and ethanol has caused serious lab fires.
- Potassium permanganate and sulfur has resulted in flash fires.
Chemicals should never be stored inside a fume hood, on the floor, on benchtops, in walkways or exit paths, near heat sources, or in direct sunlight. And one rule students commonly forget: never return unused chemicals to their original stock containers. Even if the chemical looks untouched, it may have been contaminated by contact with other substances or dirty glassware, and putting it back risks ruining the entire supply.
Fume Hood Misuse
A fume hood protects you from inhaling dangerous vapors, but only when used correctly. Common mistakes include raising the sash (the glass shield) too high while working, which reduces the hood’s ability to contain fumes. Storing bottles and equipment inside the hood disrupts airflow and reduces containment. Placing anything on the hood’s sill can prevent you from slamming the sash shut in an emergency. A fume hood also isn’t designed to contain high-velocity releases of particles unless the sash is fully closed, so reactions that could splatter or produce projectiles need the sash down.
PPE Worn in the Wrong Places
Personal protective equipment protects you in the lab, but wearing it outside the lab spreads contamination. Gloves and lab coats must not be worn in cafeterias, lunchrooms, conference rooms, offices, libraries, or any common area. For labs working with human pathogens or sterile products, lab coats cannot leave the laboratory at all. This means you remove your gloves before touching door handles, elevator buttons, or your phone. If you walk to the break room in your gloves, you’ve just transferred whatever was on that bench to every surface you touched along the way.
Inside the lab, loose-fitting clothing, dangling jewelry, and unrestrained long hair are prohibited around any equipment with moving parts. These can get caught in centrifuges, drills, or other machinery and pull you in.
Improper Waste Disposal
Laboratory waste is not regular trash, and treating it that way creates serious hazards. Sharps like needles, broken glass, pipettes, slides, and Petri dishes go into designated puncture-resistant sharps containers, never into regular trash bins. Used needles should never be recapped, especially after contact with chemicals, because the recapping motion is one of the most common causes of accidental needle sticks.
Chemical waste, including solvents like xylene, toluene, methanol, and formaldehyde, cannot be poured down the drain. Neither can biological waste such as microbiological cultures, blood, body fluids, or contaminated animal tissue. These require specific disposal routes: chemical waste goes into labeled collection containers sorted by compatibility, and biological waste is typically autoclaved (heat-sterilized) before disposal. Pouring incompatible chemical wastes into the same container creates the same explosion and toxic gas risks as mixing incompatible chemicals on the bench.
Common Student Errors Worth Noting
If you’re filling out a worksheet for a class, a few additional “don’ts” come up repeatedly in educational settings. Not taring (zeroing) the balance before weighing a sample throws off every measurement that follows. Failing to record data immediately, thinking you’ll remember the number later, is one of the most common sources of error in student labs. Rushing through steps or skipping parts of the procedure leads to contaminated results or unsafe conditions. Starting with dirty glassware introduces unknown contaminants that make your results unreliable in unpredictable ways.
Unauthorized people should never be in the lab. If you’re a student, that means don’t bring friends to watch, and don’t let anyone handle materials they haven’t been trained on. Every person in a laboratory should know the hazards present and the emergency procedures for that specific space.