Minimizing the risks of hazards requires an evaluation of an entire experiment and a review of the chemicals used and produced, as well as the equipment, procedures, and PPE.
This step-by-step procedure enables you to discover and collect this information for your particular situation while reviewing an experiment.
- Identify methods and safe practices to minimize the risks from exposures to chemicals and from physical hazards.
- Understand the nature and limitations of personal protective equipment, chemical hoods, and other safety equipment.
- Locate online and printed materials to identify safe practices, and consult with more experienced chemists.
- Wear personal protective equipment such as splash goggles, lab coats or aprons, and appropriate gloves. The dress code in a lab should be such that there should be no exposed skin below chest level.
- Use appropriate waste containers when discarding chemicals.
Before an Experiment
Pre-experiment analysis may be the most important step you can take to minimize the risks in any laboratory setting.
Incidents can happen even in the best-prepared scenario, however, careful attention to detail can minimize the risks.
- Carefully develop a list of all of the chemicals used and the quantities needed in an experiment:
- Review the SDS for each chemical and evaluate any risk, keeping in mind the inexperience of your students
- Determine the minimum quantity of each chemical or solution that will be required for completion of an experiment. Build in a small excess, but avoid having large excesses that will require disposal
- Review the warnings given in the printed material that will be given to your students to make sure that all hazard information is clear and correct. If necessary, add additional information
- Identify those warnings that must be reinforced in the pre-laboratory instruction
- Be certain to fully explain and demonstrate any new procedures or techniques that will be introduced in the experiment
- Use appropriate containers for chemical distribution in the laboratory:
- Ensure that all containers used for distribution are clearly and completely labeled with the name, formula, and concentration of the chemical. Safety information, such as signal words and GHS symbols, should also be included. Chemical formulas may be confused by inexperienced students, or even by experienced students who are rushing to complete an assignment
- Use dispensing bottles for solutions, if possible. Students will then take only the amount needed and will not be left with excess reagent. This procedure also minimizes the risk of contamination of an entire bottle of reagent
- Use several small bottles rather than one large bottle for solutions, if dispensing bottles are not available. This will minimize the risk of spillage, and the small bottles are also easier to handle and pour. In addition, if a student pours excess reagent back into a small bottle—which, of course, is poor technique because of the risk of pouring into the wrong bottle or adding adulterated chemicals—there is less risk of contaminating the entire stock
- Use bottles with droppers or attach a test tube with a dropper, if using solutions that require drops rather than larger volumes, such as pH indicators. Disposable droppers may be used but must be carefully discarded after use to prevent cross-contamination
- Provide a scoop or spoon to remove the contents of solid materials, again taking care to avoid cross-contamination
- Stress the importance of closing or capping all containers after chemicals are removed
- Review procedures for student disposal of excess reagent
- Consider the physical arrangement and the facilities available in your laboratory:
- If an experiment involves the production of volatile materials, or if you are using flammable solvents, ensure that there are adequate fume hoods and ventilation to provide a safe environment.
- Determine whether stock reagent requires the use of a fume hood or can be placed in a central location.
- The source of heat for an experiment is an important consideration, particularly if any flammable solvents are used. Common laboratory hot plates are NOT designed for the heating of flammable or combustible chemicals. In no case should a burner be used to heat a flammable or combustible chemical. If flammable materials need to be heated, this should be done in small quantities in a hot water bath and in a fume hood. Never use a burner near a flammable substance. If no flammable materials are present and burners are used, they should be checked to ensure that the hoses and mechanical parts are in good condition.
- If glass apparatus must be assembled (e.g., as in a filtration or distillation), it must be securely held to avoid breakage. Any apparatus assembled by the students must be checked for safety by the teacher before use.
- Check that fire extinguishers, eyewash stations, and safety showers are working and unblocked.
- Remove stools or other equipment that may block aisles.
- It is possible that one or more of your students have been identified as requiring accommodation because of special needs, either physical or developmental. In planning the experiment, take particular note of these requests for reasonable accommodation and the best and safest way to address any special needs of your students.
During an Experiment
Students should be closely and carefully supervised in the laboratory at all times. The teacher must be physically present during the entire experiment, concentrating on the students the entire time. Even a momentary lack of attention or absence could result in the escalation of an incident or emergency situation. Teachers need to have their full attention on all aspects of the laboratory work at all times.
- During the pre-laboratory instruction, be sure to point out:
- Potential hazards of the chemicals used;
- Safety considerations in the use of chemicals;
- Proper use of PPE;
- Steps in the procedure that are new to the students or that require particular attention;
- Methods of disposal of excess reagent or the products of a reaction; and
- Emergency procedures specific to the experiment and materials.
- Students and teachers must wear the appropriate personal protective equipment (PPE) and clothing. The basic requirements are listed here:
- Chemical splash goggles are an absolute requirement in all chemistry laboratories and should be worn at all times
- Laboratory aprons, coats, and gloves should be used to protect clothing and skin
- Gloves must be changed as soon as they are contaminated.
Contaminated gloves as well as aprons and coats must be disposed of properly
- Long hair must be pulled back, and clothing must be tucked in
- Jewelry should be removed
- Open-toed shoes or sandals are not allowed in the laboratory
- Be aware of student handling of chemicals, use of equipment, and good housekeeping procedures:
- At the dispensing center of a reagent, monitor spillage and contamination. Clean up any spillage immediately, using correct procedures and materials.
- Students should take only the amount required of each reagent. If there is excess, it must be disposed of properly and not returned to the reagent container.
- Dry chemicals should never be placed directly on balance pans. Weighing paper, weighing dishes, or small beakers may be used to hold dry chemicals.
- Make sure that all apparatus is properly set up before students are allowed to proceed with an experiment.
- No mixing of chemicals should be allowed, other than that specified in an experimental procedure.
- Chemical products should be turned in or disposed of properly.
After an Experiment
The work is, of course, not completed when the students have finished the experimental procedure.
- Before the students leave the laboratory, they should:
- Return any chemicals (excess reagent, product, or waste) to the appropriate location, or dispose of them as instructed;
- Clean any used glassware and return the items to the appropriate location; and
- Wipe down the work surfaces
- The teacher should also ensure the following:
- Returned glassware and equipment are clean and in usable, undamaged condition;
- Reagent containers are clean, closed, and properly stored;
- Chemicals requiring disposal are correctly handled;
- Unforeseen events are completely documented to prevent repetition;
- Work surfaces are left clean and dry; and
- All gas outlets are closed, especially (but not only) if burners were used during the experiment.