Chemical Hazards

NFPA Notation for Rating Chemical Hazards

Information concerning the hazards associated with a chemical can be obtained quickly from a notation developed by the National Fire Protection Association (NFPA). OESO has documented this classification system at the following link: https://www.safety.duke.edu/sites/default/files/Section_6_FireSafety.pdf. This notation uses a diamond shaped symbol which is subdivided into four square segments. The left segment indicates health hazard which includes both contact with the chemical and inhaling the fumes from the chemical, the top segment indicates flammability, the right segment indicates instability, and the bottom segment is reserved for special warnings. A number is used in the first three segments to indicate the degree of hazard with 4 implying severe hazard, 3 for serious hazard, 2 for moderate hazard, 1 for slight hazard, and 0 for minimal hazard. If one of these first three segments is left blank or contains a dash; it does not mean that it is safe, but rather means that it has not yet been included in the NFPA listing. In the fourth segment; the notation, W with a line drawn through it is used to warn of a possible violent reaction with water, and the notation, OXY, is used to warn of a strong oxidizing agent which may react explosively with combustible materials. See the sample given below.

Image result for national fire protection association system for classification of hazards 4 = Severe Hazard 3 = Serious Hazard 2 = Moderate Hazard 1 = Slight Hazard 0 = Minimal Hazard

It should be remembered that the ratings given in the NFPA system apply to the pure chemical and generally represent the "worst case scenario". Aqueous solutions of the chemical are usually less hazardous than the pure chemical. In general, the more dilute the solution, the less hazardous it becomes. Even so, as a general policy you should avoid contact with and inhaling the vapors of all pure chemicals and their solutions.


There are few greater potential hazards around the laboratory than that of unmarked or improperly labeled chemicals. All chemicals must have complete identification securely fastened to the container. Chemicals of unknown stability and those which deteriorate with age shall have a preparation date clearly indicated on the label. Disposal of unlabeled bottles is dangerous and therefore very expensive and tightly regulated by law. Research Directors will be required to pay the costs for removal of unlabeled bottles in their areas if their students have been responsible for producing them. The purpose of proper labels is multifold:

  • They are required.
  • They indicate the source, supplier, or manufacturer of the chemicals.
  • They indicate the age of the chemical.
  • They warn about the possible hazards.

Each research group should have some type of actively updated inventory of the chemicals in their laboratories.  Most chemistry laboratories use an excel spreadsheet to maintain an active chemical inventory.  

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Laboratory Cleanliness

  1. The laboratory should be kept clean and free from clutter, by regular maintenance. Do not let unused equipment or chemicals accumulate in the lab.
  2. Reagent bottles must be properly labeled - when pouring hold the bottle with its label to your palm to protect the label. Notify your safety officer of bottles whose contents are in doubt.
  3. Never eat or drink in the lab - never use lab equipment as a food or drink container.

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Transport of Chemicals

  • Never transport open containers of chemicals through the hallways, stairs or in the elevator. All chemicals, with the exception of those contained in sealed metal cans, are to be transported in rubber buckets or chemical transport carts (with special dividers to hold glass bottles). Stockroom personnel have been instructed not to allow any chemicals, except those in sealed metal can, to be removed from the stockroom unless they are transported in a rubber bucket or a chemical transport cart. Research groups which must transport large amounts of chemicals have purchased one or more rubber buckets and keep these available in their labs. Persons who transport chemicals less frequently may borrow a rubber bucket to transport chemicals from the stockroom to their labs. Borrowed buckets must be returned to the stockroom or left in the corridor for someone else to use.
  • Do not use a cart without side rails for transporting reagents in glass bottles even when the bottles are in rubber buckets since the buckets may fall from the cart and the bottles may break.
  • Gas cylinders must be transported in approved carts with the cylinders secured by straps and capped.

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Rules for Chemical Storage

  1. Avoid overhead storage of hazardous liquids and dangerous solids.
  2. Use flammable or corrosive cabinets for most storage.
  3. Refrigerate flammables only in approved flammable storage refrigerators.
  4. Maximum separation of reactive chemicals minimizes risk. Therefore, don't store chemicals in alphabetical order--store by category. Do not store mutually-reactive chemicals near each other - e.g. sodium near the sink or in a sprinkled storage area, acids near bases, organometallics near alcohols. See this manual and "Prudent Practices in the Laboratory: Handling and Disposal of Chemicals" p. 54 for tables of chemical incompatibilities. Contact OESO or the Departmental Safety Coordinator for a suggested shelf pattern for storage of chemicals.
  5. Date ethers and other peroxide-forming compounds upon arrival and follow directions for storage, testing and disposal given in this manual.
  6. Respiratory assailants and "stench" compounds should be stored in a properly vented storage cabinet.
  7. Store cleanup kits close to storage areas.

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General Chemical Hazards

All chemicals should be regarded as potentially dangerous. Before working with chemicals with which you are unfamiliar, consult the Particularly Hazardous Substances List (Table IV of this manual) and the other tables at the end of this manual or another book (see Bibliography). You should become aware of the following possible hazards: toxicity (often quoted in terms of the threshold limit value, TLV, given as PPM of air by volume, which should not be exceeded); PEL (OSHA Permissible Exposure Limit); flammability; ignition temperature; and carcinogenic properties; and you should also know the recommended method of disposal for the chemical.

  1. Gases. Other than sudden release of pressure risks, toxicity, due to buildup of high concentrations in the air, is the most general hazard. Toxicity and recommended maximum cylinder size for some common gases are listed in Table I.
  2. Other gases and volatile liquids. Explosive and toxic properties of common chemicals are listed in Table II.
  3. The Duke Particularly Hazardous Substance (PHS) List can be accessed through the following link: https://www.safety.duke.edu/laboratory-safety/chemical-hygiene/particularly-hazardous-substances.

Selected Types of Hazardous Substances

  • Organic peroxides. These are among the most hazardous chemicals normally handled in the laboratory, being explosive and extremely sensitive to shock and other forms of accidental ignition. Take advice or consult the bibliography before using peroxides.

    Although some types of peroxides can be handled with relative safety, an insidious and treacherous hazard concerning peroxides is their formation from certain classes of compounds after exposure to the air. Specific examples are: 1,4-dioxane, ethyl ether, isopropyl ether, THF, tetralin, cyclohexene, decalin. See Dr. Woerner in room 220 for a complete list of peroxide forming chemicals.

  • Ethyl ether and isopropyl ether. Containers should be labeled with the date they are purchased and should be tested for peroxides or disposed of within three months after opening. Ethers should be stored in dark bottles (to reduce photolytic oxidation), refrigerated, with the date of purchase on the label. If the ether has stood for over three months it should be tested for peroxides by shaking several ml. with an equal volume of 2% aqueous KI solution and a few drops of dilute aqueous HCl or H2SO4. Development of a brown color, or purple-black in the presence of starch, indicates the presence of peroxides. Alternatively, peroxide test strips can be obtained from the OESO. To remove peroxides, shake with a concentrated solution of ferrous sulfate, or sodium sulfite. Chromatography through a column of alumina is also effective. For additional information, see the section titled "A Guide to the Safe Use of Peroxide-Forming Compounds", in the University Chemical Hygiene Plan, or contact the OESO (9-684-2794). More detailed information and procedures can be found in ""Prudent Practices in the Laboratory: Handling and Disposal of Chemicals" p. 162. Each research group should have a copy of this valuable book. In checking for peroxides and destroying them, the major responsibility for keeping track of the age of ether samples, detecting peroxides and destroying them is yours. Only particularly old and dangerous looking ether cans and bottles should be made the concern of the OESO. Never move an old bottle of the above ethers which has developed white crystals at the bottom. These may be peroxide crystals. Call the OESO and warn others to stay away from the bottle until it can be removed safely. It may detonate when touched! Never use ether for an extraction until it has been tested for peroxides. It may explode during subsequent distillation. Although lithium aluminum hydride destroys peroxides and removes excess water from ethers, it is a dangerous drying agent. NEVER USE LiAlH4 TO DRY ETHERS. Use benzophenone and sodium as recommended below. A superior alternative to the use of LiAlH4 for drying ethers and other solvents is a mixture of sodium and benzophenone. This may be prepared by adding about 5 g of chunk sodium to 10 g of benzophenone in 2 l. of the solvent to be dried. This should be done under nitrogen since the mixture reacts with oxygen. A purple solution results, from which the dry solvent is distilled. Appearance of a brown or greenish yellow color indicates the depletion of the drying agent. This is a safe way of removing water, oxygen and peroxides, while leaving no dangerous residue for disposal. For a useful reference to articles about drying agents and their abilities see D. R. Burfield and R. H. Smithers, J. Org. Chem., 43, 3966 (1978).
  • Cyanides and nitriles Store away from acids. Because of the extreme toxicity of cyanides and nitriles, ampoules of amyl nitrite should be kept in laboratories where these chemicals are used. In an emergency, amyl nitrite should be held under the affected person's nose for about 15 seconds and then at intervals until help arrives.
  • Organic solvents Among the more common solvents, benzene (TLV 10 PPM; PEL 1 PPM) and carbon tetrachloride) (TLV 5 PPM; PEL 2 PPM) are particularly hazardous; the latter is readily absorbed through intact skin to produce chronic damage to the liver and kidneys.
  • Perchloric acid and perchlorates All perchlorates should be considered as very explosive, especially on contact with organic materials. Many, particularly all metal amine complexes, and perchlorates, are extremely shock sensitive, powerful explosives. Periodates and chlorates are similar hazards.
  • Mercury Mercury should be stored in polyethylene containers - not in glass bottles, because of the risk of breakage. Spilled mercury should be, immediately and painstakingly, cleaned up preferably by OESO personnel, or by using a trapped vacuum line. Materials for cleaning up small mercury spills are available in the Gross Chemistry Stockroom (room 206A). Independent of who is to clean up the spill, contact the OESO, 9-684-2794. Recovered mercury should be placed in a closed container and tagged for hazardous waste pickup. Contact the OESO to clean up any mercury you cannot recover.
  • Alkylating agents All powerful methylating agents are extremely toxic. The toxicity of iodomethane, dimethyl sulfate and diazomethane are well known. When these reagents are of inadequate reactivity, methyl fluorosulfate, methyl trifluoromethanesulfonate (triflate) and trimethyloxonium salts are frequently used. Methyl triflate has almost identical volatility to methyl fluorosulfate, is slightly more reactive but more expensive. Trimethyloxonium salts are more reactive in most cases, and may offer a safety advantage because of their low-volatility. Being hygroscopic solids of low solubility, they are more difficult to handle, and this may introduce its own safety penalty.
  • We conclude that the alkylation of unreactive substance using, of necessity, powerful alkylating agents, is probably an inherently hazardous chemical operation and should be approached accordingly.

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Specific Hazards of Selected Chemicals

It would be impossible to list all of the possible chemical hazards which might be encountered in laboratories. A few of the most commonly used hazardous materials are listed below.

  • Nitric Acid In addition to its corrosive properties, and the highly toxic properties of its oxides, nitric acid is a powerful oxidizing agent and forms flammable and explosive compounds with many materials. Paper, which has been used to wipe up nitric acid spills, can ignite spontaneously when dry and should not be thrown into a waste basket until first rinsed with water and neutralized. Highly flammable materials such as ethers, exposed to nitric acid may spontaneously ignite. A mixture of nitric acid and acetone has been known to explode upon standing. Storage of nitric acid should always be away from combustible materials including organic acids such as acetic acid.
  • Perchloric Acid This acid forms highly explosive and unstable compounds with many combustible materials and even with metals. Wood or asphalt tile on which perchloric acid has been spilled may spontaneously ignite. Perchloric Acid should be used with extreme caution and only in a fume hood specifically designed for this use. Perchloric and sulfuric acid, when mixed, produce anhydrous perchloric acid which will ignite any organic matter (e.g., wood) and/or explode spontaneously. Explosive crystals may form in perchloric acid bottles stored over long periods. For this reason, bottles should not be stored for more than one year.
  • Picric Acid (2,4,6-trinitrophenol) This acid may form explosive compounds with many combustible materials. It may also lose water and become unstable after extended periods of storage. It should be stored wet, and, away from combustible materials and should not be kept for extended periods.
  • Hydrofluoric Acid This acid is extremely corrosive, even attacking glass, and unlike the other halogen acids, is also extremely toxic. It is volatile and will attack skin and eyes. Burns from hydrofluoric acid heal slowly and with great difficulty. There is a chance of nerve damage resulting from all HF exposure. It forms toxic fumes in contact with metals or ammonia. It should be handled only in an adequate fume hood while wearing appropriate personal protective equipment. Inhalation can be fatal. Call the ambulance at once if taken into the lungs.
  • Mercury The vapor pressure of mercury at room temperature is about 1 micron which is sufficient to produce a concentration which is several times the allowable concentration for continuous exposure. Although this concentration is not likely to occur with small spills in a well ventilated laboratory, every effort should be made to avoid mercury spills and to clean up spills which do occur. Care should be taken not to heat mercury in open vessels or to heat equipment contaminated with mercury. Mercury or mercury compounds should never be disposed of by sewer. Mercury vapors from thermometers which have broken in hot oil baths and ovens are a common hazard. To be safe, whenever spills occur, the OESO should be notified immediately.
  • Lead Lead may give off toxic vapors when heated. Lead compounds in the form of finely divided powders may be carried by air currents. Lead and lead compounds, like and heavy metal, should not be disposed of by sewer. People using lead and lead compounds are required by OSHA to have special training. Contact the Safety Coordinator before beginning to schedule such training.
  • Phosphorus (Yellow) Yellow phosphorus is stored under water. It may ignite spontaneously if allowed to dry. It is extremely toxic if ingested. Gloves should always be worn when handling phosphorus. Care should be taken that the water level in the storage jar not be allowed to go below the level of the phosphorus. Material contaminated with phosphorus should be handled with great care to avoid fire hazard or exposure of personnel.
  • Ether In addition to its highly flammable properties, it may form explosive and unstable peroxides if stored over long periods. The peroxides may explode from shock or even from the friction of unscrewing the bottle cap. Tetrahydrofuran and isopropyl ether as well as the more widely used diethyl ether exhibit this dangerous property. Ether should be ordered in minimum quantities and should not be stored over long periods. Containers with visible peroxide crystals should be handled and disposed of with extreme caution by the Environmental Safety Department. Do not ever disturb such a bottle. See pages 20-21 regarding detection and removal of peroxides.
  • Carbon Disulfide Is the most highly flammable and explosive of all the common solvents. Its vapor can be ignited by contact with an ordinary light bulb or steam radiator. It is toxic, and major residual injury may result from overexposure in spite of prompt treatment. Carbon Disulfide should be handled only with adequate ventilation and protective clothing to prevent contact with the skin or eyes. Because of its low ignition temperature the danger of fire or explosion is high.
  • Active Metals (Sodium and potassium being the most common) - are stored under oil. They react violently with water and may ignite spontaneously if exposed to the moisture in air. Toxic fumes are given off during combustion. Protective clothing should be worn while handling these materials. On long term standing even when stored under oil, potassium forms a superoxide. The dry superoxide is very unstable and can explode if subjected to any form of shock.
  • Oxidizing Agents and Peroxides These materials should be obtained and stored in minimum quantities. Deterioration may occur after long storage causing an explosion hazard. Explosion hazard can be minimized by treatment with ferrous sulfate. These materials should never be stored in close proximity to flammable materials. Phosphorus pentoxide if moistened with water can easily ignite paper, for instance.
  • Organic Phosphates These compounds are related to the nerve gases developed during World War II. They are generally used as pesticides. They should be used with caution. Disposal should not be made in trash receptacles or sewers.

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Chemical Spill Clean-up

Our general "rule of thumb" for dealing with spills is as follows:

  • If you spill more than one liter of any chemical, or less than one liter of a moderately or highly hazardous chemical, or you are uncomfortable cleaning up the spill, call 911 from a "land line" phone or 919-684-2444 from a cell phone and report the spill to Campus Police. They will respond to the call and will contact the OESO who will send a spill cleanup team to do the cleanup.
  • If you spill less than a liter of a chemical that is not very hazardous (refer to the MSDS for hazard information), and you feel comfortable cleaning it up, find out how to clean it up (also found in the MSDS for the chemical) and do so, see section on spill kits below.
  • Spill Kit Adjacent to the ice machine on the first level (hallway near 1112) and located in each research lab are spill kits for handling common spills involving 1) Solvents, 2) Acids (not for use with HF spills) and 3) Bases. Directions for the use of each kit are provided with each kit. If you use one of the kits at the ice machine near 1112, notify the Lab Preparator (x1517, Room 1214) so that the used kit will be replaced.  If you use a kit located in a research lab, notify the Manager of Chemistry to obtain a replacement.  The used materials from the kit are to be kept in your lab (in a hood) and are to be treated as a hazardous waste. It is necessary to fill out a form requesting that this waste be removed from your lab by the OESO. (See the section dealing with disposal of waste chemicals later in this manual.)
  • If the spill involves some chemical not covered by the three spill kits, consult OESO (684-2794).

For more information check out OESO's Laboratory Safety Manual, Section 3.  

Last updated on 7/25/2013

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