ABC of Safety in the Biological Sciences

 

 

Handling Hazardous Chemicals

ALL chemicals are hazardous to some degree. Protect yourself from accidental skin, eye, and respiratory contact by wearing appropriate protection which should always include a long sleeved laboratory coat or gown with elasticised wrist bands, rubber gloves and safety goggles. Contact lenses should not be worn when handling chemicals.

Know the hazards of the materials you are working with. Always source appropriate safety information from a Material Safety Data Sheets, (MSDSs), before handling an unknown chemical or before attempting disposal or clean-up procedures.

General Guidelines

  • Whenever possible, perform hazardous reactions in a properly functioning hood using appropriate shielding.
  • Never taste a laboratory chemical.
  • Take special precautions when scaling up a reaction. A reaction that is safe under published conditions may be violent when multiplied in scale.
  • Read labels carefully, and keep labels clean so that they are legible. Replace deteriorating labels before a chemical becomes unidentifiable
  • Clearly labels ampoules, product vials, reaction vessels, and all other containers. Labels should include chemical names, structures when appropriate, date and name of owner. If you know of special risk, include appropriate warnings. Unidentified materials cannot be disposed of and can cause serious accidents.
  • If it is necessary to smell a chemical, do so by wafting the vapors toward your nose with your hand so that the minimum amount is inhaled.
  • Never pour a chemical back into its original bottle after measuring out too much. This can contaminate the original contents.
  • Never combine the contents of two or more bottles of the same reagent. If one of the bottles is contaminated, the resulting combination is now contaminated.
  • Be aware of chemical incompatibilities before mixing to avoid explosive or uncontrollable reactions, generation of toxic gases, etc.
Handling of Organic Peroxides
Peroxides are a group of compounds that contain an oxygen-oxygen bond. As a class, organic peroxides are the most explosive substances normally found in a laboratory. Peroxides are sensitive to light, heat, and friction, as well as to strong oxidizing and reducing agents. Explosions involving peroxides are unpredictable and usually violent.
  • Store peroxides away from sources of light, heat, friction, and mechanical disturbance.
  • A solid peroxide can often be stored more safely if it is dissolved in a nonperoxidizable inert solvent such as an aliphatic hydrocarbon.
  • Do not allow solutions of peroxides to evaporate, because the concentration of peroxide may reach a dangerous level.
  • Store solutions of peroxides at a cool temperature, but do not refrigerate peroxides at a temperature below which precipitation or freezing out of solid material may occur; in this form, peroxides are extremely sensitive to shock and heat.
  • Do not store peroxides or solutions of peroxides in glass bottles with ground glass or screw caps. The friction caused by opening the bottle can initiate an explosion. Polyethylene bottles with screw caps are more suitable.
  • Use ceramic spatulas for handling peroxides; metal spatulas can catalyze an explosive reaction.
  • Never use a naked flame in areas where peroxides are being handled.
  • Purchase, store, and use the minimum quantity of peroxide necessary. Use special caution when scaling up reactions that use peroxides.
  • Perform experiments involving peroxides in a hood and behind a safety shield.
  • Clean up all spills immediately by absorption on vermiculite or other suitable absorbent.

Peroxide-forming Chemicals -- Some chemicals can easily form peroxide when exposed to atmospheric oxygen. These peroxidizable chemicals are especially dangerous because the presence of peroxides may not be known. Check this list of peroxidisable compounds before using an organic solvent in a distallion or reaction.

Handling of Peroxide-forming Chemicals

  • Buy and use the minimum quantities of Peroxidizable substances necessary.
  • Store peroxide-forming chemicals for the shortest possible time. Date the container when it is opened. Test for peroxide formation when first opened and every 3 months. If peroxide levels are acceptable, date the container when the test was performed. If the material contains hazardous concentrations, either treat to remove peroxides or discard.
  • Peroxide formation in ethers and hydrocarbons can be prevented if they are stored under an inert atmosphere, for example, argon or nitrogen. The container should be well sealed.
  • Store peroxidizable chemicals away from source of heat, light, sparks, other ignition sources, and mechanical shock.
  • Peroxide-forming compounds should be kept at a cool temperature. Do not refrigerate peroxides if solid peroxide may precipitate or freeze out. Solid material is especially sensitive to shock.
  • Do not store peroxide-forming compounds in glass bottles having ground glass or screw caps, or metal cans with metal screw caps. Serious explosions can occur by merely unscrewing the top of a glass bottle that contains peroxides. Metal cans with plastic caps and polyethylene bottles are safer containers for ethers and other peroxidizable compounds. The safest container is the one supplied by the manufacturer.
  • Test peroxidizable substances before using, and periodically in storage
  • Peroxides may be removed from solvents by passing the solvent through a column of alumina or Dowex-1 resin. The column MUST NOT be allowed to run dry and the packing should be handled as other peroxide waste. It is less dangerous, however, to use a new bottle of peroxide-free solvent than to purify solvent containing peroxides.
  • Serous accidents can occur when substances capable of forming peroxides are distilled. Consider other methods of purification. If distillation is necessary, the following precautions should be observed where peroxide formation is suspected.
    • Test for peroxides before distilling. The peroxide test strips can indicate the concentration of peroxide in ppm. allowing you to know just how much peroxides are present.
    • Do the distillation under an inert atmosphere. Do not allow air to come in contact with hot solvent.
    • Add a suitable reducing agent to the distillation flask, such as sodium/benzophenone for ethers. Make sure that no compounds that react vigorously with the reducing agent are present in the distillation flask.
    • Do not carry the distillation to dryness; leave at least 10% liquid in the flask.
    • Wear goggles, face shield and use a free standing safety shield when distilling peroxidizable chemicals. Conduct the distillation in a hood with the sash closed.
    • Be aware that freshly distilled peroxidizable material may reform peroxide with two weeks of distillation.
  • Spills should be cleaned up immediately by absorption on solusorb or other suitable absorbents. These are located in the issue rooms or main stockroom.
Handling of Common Chemicals that are Particularly Hazardous
Many compounds found in older literature have been found in recent years to be more hazardous than once thought. When the research was preformed, these compounds were readily available and the chronic effects were not known. Therefore, if you use a procedure not recently published, you must check the MSDSs of the reagents to get the most recent information on hazardous health affects. For the compounds listed below, consider finding a substitute solvent or reactant to avoid possible risk. If you cannot find a substitute, then take special precaustions to avoid exposure.
  • Benzene is considered a Category I Carcinogen by OSHA. Chronic poisoning can occur by inhalation of relatively small amounts over a long period of time. The toxic action is primarily on the blood-forming organs. Benzene has been documented to cause leukenia. Benzene is readily absorbed through the skin. Toluene should be substituted whenever possible. OSHA permissible exposure limit is 1 ppm.
  • Carbon Tetrachloride is another dangerous solvent found in many literature references. At one time, carbon tetrachloride was used in fire extinguishers (if you ever find an old extinguisher with CCL4, contact the Chemical Hygiene Officer immediately). Keep exposure to the liquid and its vapors to an absolute minimum. High concentration in the air can lead to death from respiratory failure. Less severe exposure can lead to kidney and liver damage. In addition to inhalation hazard, it can be readily absorbed through the skin. Methylene chloride, (dichloromethane), is a much safer chlorinated hydrocarbon. However, almost all chlorinated hydorcarbons have been found to be toxic to some degree. The current threshold limit value for carbon tetrachloride is 5 ppm.
  • Chloroform is a compound similar to carbon tetrachloride with one less chlorine atom (CHCL3). Therefore, it has many of the adverse health affects as carbon tetrachloride. Repeated exposure can cause kidney, liver and heart damage. In laboratory animals it has been shown to be a carcinogen and mutagen. Use methylene chloride as a substitute. The PEL for chloroform is 2 ppm.
  • Formaldehyde use as preservative of biological tissue has been found to be a a human carcinagen. Repeated inhalation can cause cancer of the lungs, nasopharynx, and/or nasal passages. It can cause respiratory tract irritation and edema. It can also cause eye and skin irritation. Formaldehyde is a colorless, pungent, ittitant gas that is water soluble and most frequently found in 37% aqueous solution commonly known as formalin. Alway use formalin in a hood and wear gloves and splash-proof goggles. The threshold limit value for formaldehyde is 0.75 ppm.
  • Ethyl ether is an extremely flammable solvent use in Grinard reactions and extractions. The greatest danger of ethyl ether is its very low flash point (-30 C). The vapors of ether are heavier than air and can "crawl" along the benchtop to a source of ignition. Tends to form peroxides especially anhydrous. It is a depressant to the central nervous system and can cause unconciousness or even death on severe exposure. Carry out reactions using ethyl ether in the hood.
  • Perchloric Acid usually found as 72% aqueous solution is a very strong non-oxidizing acid. Contact with combustible materials at elevated temperatures may cause fire or explosion. Handle with extreme care as severe burns can result from skin contact. Wear heavy rubber gloves and apron in addition to splash-proof goggles.

 

 

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