Lab safety rules and the reasons behind them

TL;DR:

• Every lab rule exists because of a specific way people get hurt. Knowing the reason makes the rule easy to remember.

• Wear splash goggles, keep food and drink out, label everything and add acid to water, never the reverse.

• Know where the eyewash, shower, exits and fire blanket are before you start, and tell your teacher about any spill or injury.

On the first day in a chemistry lab you get a list of rules. It is tempting to treat them as fussy. They are not. Each one traces back to a way someone has been hurt, and once you see the reason, the rule is much easier to follow when you are rushed or tired.

Follow your own lab first: This article explains general reasons. Your teacher's instructions, your school's rules and the safety data sheet for each chemical come first. Do chemistry experiments only in a supervised lab, not at home.

Protect your eyes, skin and lungs

Wear splash goggles all the time. Eyes are the most easily damaged and the hardest to repair. A drop of acid or base that would be a minor burn on your arm can cause serious harm in an eye. Ordinary glasses do not seal against splashes, so wear goggles over them.

Tie back long hair, wear closed shoes, long trousers and a lab coat. Hair catches fire in a flame. Open shoes leave skin exposed to spilled liquid and broken glass. Sleeves and loose clothing can drag through a flame or knock over glassware.

Never smell or taste chemicals directly. Some fumes damage your airways. If you are told to check a smell, hold the container a safe distance away and gently waft the air toward you with your hand, and only if your teacher says so.

No food or drink, and wash up

Food and drink are banned because chemicals can get into them without you noticing. Lab glassware, benches and your hands can carry traces of substances that should never be swallowed. Beakers must never be used as cups, and nothing from a lab is ever tasted.

Wash your hands at the end, even if you wore gloves. Gloves can tear, and chemicals can transfer from gloves to your face when you touch it.

Label everything

An unlabelled bottle is a hazard because no one knows what it contains or how to deal with it. Label every container with the substance, concentration, date and your name. Read a label twice before you pour: once when you pick it up and once before you use it, because many bottles look alike.

Worked example: diluting acid the safe way

Your teacher asks you to prepare 100 mL of 1.0 M acid from a 6.0 M stock, under supervision, with goggles and gloves on. Use M₁V₁ = M₂V₂ from molarity and dilution.

1. Calculate: V₁ = (1.0 × 100) / 6.0 = 16.7 mL of stock.

2. Check by moles: stock gives 6.0 × 0.0167 = 0.100 mol. The final solution has 1.0 × 0.100 = 0.100 mol. They match.

3. Put about 70 mL of water in a 100 mL volumetric flask or a beaker with a stirring rod.

4. Pour in the 16.7 mL of acid slowly, stirring gently.

5. Add water up to the 100 mL mark, mix and label.

The order matters. Mixing concentrated acid and water releases heat. If you add a little water to a large amount of concentrated acid, that heat is released in a small volume of liquid and can make it boil and spit. If you add the acid slowly to a large amount of water, the water absorbs the heat. The rhyme is: add acid to water.

Know your exits and equipment

• Eyewash and shower. Know where they are before you need them. If chemicals reach your eyes or skin, you rinse with a lot of water, and standard guidance is at least 15 minutes. Follow your lab's posted procedure, and tell the teacher at once.

• Exits and alarm. Learn two ways out. In an emergency, leave the room calmly, as instructed.

• Fire blanket and extinguisher. Learn where they are. Do not try to fight a fire you are not trained for.

• Spills and broken glass. Tell your teacher before cleaning up. Do not pick up broken glass with bare hands.

• Hot glass. Hot glassware looks the same as cool glass. Handle it with tongs or holders.

How to check yourself before you start

• Are goggles on, hair tied back and shoes closed?

• Have you read the instructions and the hazards, and do you know what to do if something goes wrong?

• Is everything labelled, and is your bench clear?

• Do you know where the eyewash, exits and the teacher are?

Mistakes that cause accidents

• Pouring water into concentrated acid.

• Pointing a heated test tube toward a person, including yourself.

• Working alone or leaving a heat source unattended.

• Returning unused chemical to the stock bottle, which can contaminate it.

• Pouring waste down the sink without checking the disposal instructions.

• Being embarrassed to report a spill or injury. Report it immediately.

Where you will use it next

Good habits apply in every lab course. The ideas about acids and bases you handle appear in three ways to define acids and bases, and the first lab skill to practise is the sort of titration described elsewhere.

Frequently asked questions

Why can't I wear contact lenses in some labs?

Policies vary. Concerns include fumes getting trapped under the lens. Follow your school's rule and always wear goggles.

What should I do if I am unsure about a step?

Stop and ask your teacher. A question costs a few seconds, and a guess can cost much more.