Preparing to use chemicals in the lab starts well before you touch a single bottle. The core of good preparation is knowing what you’re working with, what protective gear you need, and what to do if something goes wrong. Most lab accidents happen because someone skipped one of these steps, not because the chemistry itself was unpredictable.
Read the Safety Data Sheet First
Every chemical in your lab has a Safety Data Sheet, commonly called an SDS. This is a standardized 16-section document that tells you everything you need to know about a substance’s hazards, protective requirements, and emergency procedures. Before you handle any chemical for the first time, you should review at least three key sections of its SDS.
Section 8 covers exposure controls and personal protection. This is where you’ll find exactly what kind of gloves, eye protection, and ventilation the chemical requires. It gets specific: for example, it will tell you whether you need nitrile gloves versus PVC gloves, and how long those gloves can resist the chemical before it breaks through. Section 4 covers first-aid measures, organized by how you might be exposed (inhaling it, getting it on your skin, splashing it in your eyes, or swallowing it). It also lists the symptoms you’d experience, from mild to severe. Section 11 provides toxicological information, including whether the chemical is a known carcinogen, whether it causes organ damage over time, and whether its effects are immediate or delayed.
Your instructor may point you to these sections, but don’t wait to be told. Pull up the SDS yourself. They’re freely available online from chemical manufacturers and through your institution’s safety office.
Learn the Hazard Pictograms on Labels
Chemical labels use a set of standardized diamond-shaped pictograms from the Globally Harmonized System (GHS). Recognizing these at a glance helps you identify dangers before you even open a container. There are nine pictograms, and each one flags a different category of risk:
- Flame: The chemical is flammable, self-heating, or emits flammable gas.
- Flame over circle: It’s an oxidizer, meaning it can intensify a fire by supplying oxygen.
- Skull and crossbones: Acutely toxic. Exposure can be fatal or cause serious poisoning.
- Corrosion: Causes skin burns, serious eye damage, or corrodes metals.
- Exclamation mark: An irritant to skin or eyes, or harmful at lower toxicity levels than the skull symbol.
- Health hazard: Long-term dangers like cancer risk, reproductive toxicity, or organ damage.
- Gas cylinder: Contents are under pressure and may explode if heated.
- Exploding bomb: Explosive or self-reactive under certain conditions.
- Environment: Toxic to aquatic life (this one is non-mandatory in some settings).
A single chemical can carry more than one pictogram. Concentrated sulfuric acid, for instance, is both corrosive and a health hazard. Knowing this before you start working shapes every decision you make about gear, ventilation, and handling.
Wear the Right Protective Equipment
The baseline for nearly any chemistry lab is safety goggles (not just glasses), a lab coat, closed-toe shoes, and chemical-resistant gloves. But “chemical-resistant” doesn’t mean one glove fits all situations. Nitrile gloves resist many organic solvents, while latex gloves do not. The SDS for your specific chemical will tell you which glove material to use and how long it provides protection before the chemical starts to seep through.
Eye protection matters more than students often realize. Standard safety glasses block impacts but leave gaps around the edges where splashes can reach your eyes. Chemical splash goggles form a seal against your face and are the correct choice whenever you’re pouring, mixing, or heating liquids. If you get a chemical in your eyes despite wearing protection, lab eyewash stations are designed to flush for at least 15 minutes continuously.
Long hair should be tied back, and loose clothing or dangling jewelry should be secured. These aren’t minor rules. A sleeve that dips into a beaker or hair that catches a flame creates an emergency in seconds.
Know Your Ventilation Setup
Many chemicals release fumes that are toxic, irritating, or flammable. A chemical fume hood pulls air away from you and vents it safely out of the building. When your procedure calls for a fume hood, keep the glass sash lowered to between 12 and 18 inches while you work. At that height, the hood maintains an air capture velocity of about 100 feet per minute across the opening, which is fast enough to keep vapors from escaping toward you.
Don’t store extra chemicals or equipment inside the hood. Clutter disrupts airflow and reduces its effectiveness. Keep your materials at least six inches behind the face of the hood, and never stick your head inside while a reaction is running. If the fume hood has an alarm or airflow indicator, check it before you begin. A hood that isn’t pulling air properly offers no protection at all.
Understand Chemical Incompatibilities
Certain chemicals react violently when they come into contact with each other, and some of these combinations are surprisingly common in student labs. Concentrated sulfuric acid and concentrated sodium hydroxide react with extreme heat. Chlorine and ammonia produce toxic gas. Oxidizers like potassium permanganate should never be stored or mixed with carbon-based powders. Calcium hypochlorite (bleach powder) reacts dangerously with moisture and oils.
The general storage rules are straightforward: keep liquids and dry chemicals in separate areas regardless of their other properties, store chemicals from different compatibility groups apart from each other, and give chlorine and ammonia their own isolated storage away from everything else. In practice, this means checking that the chemicals you’re bringing to your bench for a procedure won’t cause a problem if they accidentally mix from a spill.
Follow the Right Order When Mixing
One of the most important safety rules in chemistry is deceptively simple: always add acid to water, never water to acid. The classic memory aid is “Do as you oughta, add acid to water.”
The reason is physics. Concentrated acid is denser than water, so if you pour water into acid, the water floats on top. The enormous heat released when the two mix (called dissociative energy release) can boil that thin water layer instantly, launching hot acid out of the container. When you add acid slowly to a larger volume of water instead, the heat disperses safely through the water. This same principle applies to strong bases. Always add the concentrated substance into the larger volume of dilute liquid, slowly and with stirring.
Label Everything Correctly
Any time you transfer a chemical from its original container into a secondary one, like a beaker, wash bottle, or smaller flask, that new container needs a label. OSHA requires that secondary containers display the product name and enough hazard information (words, symbols, or pictures) for anyone in the lab to identify what’s inside and what dangers it poses. You don’t need to replicate the full manufacturer label, but at minimum, someone walking up to your container should be able to tell what the chemical is and what risks it carries.
Unlabeled containers are one of the most common and most preventable hazards in student labs. If you can’t identify a liquid in a beaker, you can’t respond correctly to a spill, you can’t dispose of it properly, and you can’t avoid mixing it with something incompatible.
Handle Waste Properly
Chemical waste doesn’t go down the drain unless your instructor explicitly says it does. Most lab chemicals are collected in designated waste containers, often in a satellite accumulation area near your workstation. These containers must be labeled with the words “Hazardous Waste” along with a description of what’s inside and its hazards. According to EPA regulations, waste containers must stay closed at all times except when you’re actively adding or removing waste. For liquid waste, that means all lids and caps are securely fastened. For solid waste, the lid must make complete contact with the rim all the way around.
Never mix different types of waste in the same container unless instructed to. Combining incompatible chemicals in a waste bottle can cause the same violent reactions you’d see on the bench. If you’re unsure which waste container to use, ask before you pour.
Locate Emergency Equipment Before You Start
Before your first day of working with chemicals, walk the lab and identify the locations of the eyewash station, the emergency shower, the fire extinguisher, the fire blanket, and the nearest exit. In an emergency, you won’t have time to search. Eyewash stations require a full 15 minutes of flushing after a chemical splash to the eyes, so knowing exactly where yours is saves critical seconds. Emergency showers serve the same purpose for larger skin exposures.
Know your lab’s spill kit location and what it contains. Small spills of non-volatile, non-toxic chemicals can often be cleaned up with absorbent materials from the kit. Larger spills or anything involving highly toxic, flammable, or reactive chemicals should be left for trained personnel. Your job in that situation is to alert others, evacuate the immediate area, and notify your instructor.