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Planning and Carrying Out Experiments

Planning Experiments

It is expected that time and care will be taken by all occupants of French Family Science Center in PLANNING EXPERIMENTS. [The following material is taken from a safety booklet prepared by the Mallinckrodt Laboratory Safety Committee. This booklet is no longer available.] In order to foresee and avoid some of the booby-traps in a laboratory experiment:

  • List all possible reactions, including side-reactions, before beginning.
  • Think through all reactants, intermediates, and products in terms of flammability, toxicity, and reactivity hazards.
  • Follow recognized safe practice procedures concerning protective equipment, housekeeping, the handling of hazardous chemicals and of equipment, as outlined earlier.
  • In an unknown reaction, always start with small quantities of material and carefully observe reaction characteristics, such as temperature, color, viscosity, and physical state.
  • Obtain safety information about reactants and possible products from Material Safety Data Sheets (MSDS). If the safety information is not available elsewhere, it may by obtained from some outside laboratories that offer a testing service for the evaluation of explosion hazards, etc.
  • If possible, determine from thermodynamic and kinetic considerations, the total quantity of, and the rate of evolution of heat and gases to be released during the reaction.
  • Provide adequate cooling, ventilation, pressure relief, and gas purging. Isolate the reaction vessel, if possible, and make frequent inspections of equipment during reaction.
  • Do not leave a hazardous system unattended.

For each reactant, intermediate, or product, ask:

  • What is its flash point, flammability range, auto-ignition point, vapor pressure and vapor density?
  • Does it decompose and if so, how rapidly and to what products? What is its stability on storage to heat, light, water, metals, etc.?
  • Is it impact sensitive?
  • Is it toxic? If so, what is the type of hazard (inhalation, ingestion, skin contact)? What protective measures are required?
  • What is the recommended first aid treatment in case of an accidental exposure?

About the reaction itself, ask:

  • How violent will it be?
  • What is the effect of catalysts or inhibitors?
  • Will water or air affect the reaction?

What would happen and what should be done if:

  • Electric power fails?
  • Cooling system fails?
  • Pressure gets out of hand?
  • Water leaks into system?
  • Reaction container falls and breaks or spills contents?

Remember that many explosions, fires, and asphyxiations are caused by the accidental combination of potentially dangerous substances.

Carrying Out Experiments

  1. Avoid working alone, especially when carrying out a new or unfamiliar reaction or operation.
    • Make arrangements with other persons in the building to check with each other periodically.
    • Never perform hazardous operations while alone.
  2. Use a towel to protect the hands when glass rods, tubing, or thermometers are being inserted or removed from rubber stoppers or when trying to loosen ground glass joints that are stuck.
  3. Do not use flawed glassware. Chipped or cracked glassware can produce serious cuts, explosions, or bad spills.
  4. All electrical equipment should be properly grounded. Use of extension cords should be avoided.
  5. In working with fume hoods the following facts should be kept in mind.
  6. Lowering the sash will increase air velocity and offer greater protection from toxic fumes and will provide supplemental eye and face protection. Normally the sash opening should be less than 18". If the sash is opened to a height greater than 18", an alarm is activated. It is important to keep the sash below the 18" mark. The OESO periodically measures the airflow in the fume hoods. They have labeled the hoods the maximum recommend sash height. If the sash is raised above the indicated height, then the airflow will fall below the minimum acceptable level of 75 feet per minute. If you have questions about the airflow in your fume hood, contact the OESO at 684-2794.
  7. Placing equipment deep in the hood will also reduce the possibility of fumes escaping into the laboratory.

Personal Safety Considerations

  • Gloves should be worn when handling:
    • Most kinds of organic chemicals. If in doubt, assume they are carcinogenic, toxic or allergenic.
    • Corrosive materials.
    • Radioactive materials.
    • Pathological microorganisms.
    • Large quantities of volatile solvents.
    • Any highly poisonous substance.
  • A lab coat or apron should be worn when working with hazardous materials.
  • Use a protective shield for unfamiliar or potentially hazardous reactions.
  • Wash hands often — always before eating, smoking, or leaving the laboratory. Washing should be an instinctive reaction to spillage of any chemical on the skin.

Reactions involving solutions

  • No solutions should be pipetted by mouth. An aspirator bulb or vacuum line should be used.
  • Add the more concentrated solution to the less concentrated — e.g. concentrated acid to water, not water to acid.
  • Never mix concentrated solutions of highly reactive materials together without careful planning.
  • Avoid accidentally mixing incompatible chemicals. Since both HNO3 and alcohol are often used for cleaning, it is easy to inadvertently make an explosive mixture approaching nitroglycerine in sensitivity and destructive power!
  • Do not add a solid to a liquid near its boiling point. Bubble nucleation can produce a vigorous eruption.
  • Avoid overheating oil baths — these can spatter and flash into a flame. Never use an oil bath for heating highly oxidizing substances. (perchlorates, nitrates, peroxides).
  • Do not overfill reaction vessels — leave at least 20% free volume.
  • Place a container under a reaction vessel to contain the spillage should the vessel break.
  • Do not leave syringes with needles in positions where the needle is exposed to a working area. Needle tips on loaded syringes should be covered with a small cork or rubber septum when not actually in use. Accidental injection of most chemicals into a person will probably cause death.

Distillations

  • When possible, the heat source should be elevated on a jack or removable blocks.
  • Do not open a system to the air until the residue has cooled to avoid exothermic decomposition.

Vacuum Operations

  • Vacuum desiccators and Dewar flask should be enclosed or wrapped with tape to prevent flying glass in case of an implosion. Never carry an evacuated desiccator!
  • Do not apply a vacuum to a flat-bottomed flask.
  • Maintain a cold trap between a vacuum pump and the apparatus — do not use liquid N2 as trap coolant when pumping organic compounds (liquid O2 may condense in the trap, leading to explosive oxidation).
  • All workers utilizing the house vacuum line must be sure to use a trap to prevent volatile materials from going into the vacuum line. If the trap is not used, a dangerous amount of the volatile materials will collect along the vacuum line and in the mechanical area of the basement causing a serious fire hazard as well as a hazard to those who work in the basement.

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