Flammable liquids are among the most common of the hazardous materials found in laboratories. They are usually highly volatile (have high vapor pressures at room temperature) and their vapors, mixed with air at the appropriate ratio, can ignite and burn. By definition, the lowest temperature at which they can form an ignitable vapor/air mixture (the flash point) is less than 37.8°C (100°F) and for several common laboratory solvents (ether, acetone, toluene, acetaldehyde) the flash point is well below that. As with all solvents, their vapor pressure increases with temperature and, therefore, as temperatures increase they become more hazardous.
For a fire to occur, three distinct conditions must exist simultaneously:
Control strategies for preventing ignition of flammable vapors include removing all sources of ignition or maintaining the concentration of flammable vapors below the lower flammability limit by using local exhaust ventilation such as a hood. The former strategy is more difficult because of the numerous ignition sources in laboratories. Ignition sources include: open flames, hot surfaces, operation of electrical equipment, and static electricity.
The concentrated vapors of flammable liquids are denser than air and can travel away from a source a considerable distance (across laboratories, into hallways, down elevator shafts or stairways).If the vapors reach a source of ignition a flame can result that may flash back to a source of the vapor.
The danger of fire and explosion presented by flammable liquids can usually be eliminated or minimized by strict observance of safe handling, dispensing, and storing procedures.
While working with flammable liquids you should wear gloves, protective glasses, and long sleeved lab coats. Wear goggles if dispensing solvents or performing an operation which could result in a splash to the face. Large quantities of flammable liquids should be handled in a chemical fume hood or under some other type of local exhaust ventilation. Five-gallon containers must be dispensed to smaller containers in a hood or under local exhaust ventilation. When dispensing flammable solvents into small storage containers, use metal or plastic containers or safety cans (avoid glass containers).
Make sure that metal surfaces or containers through which flammable substances are flowing are properly grounded, discharging static electricity. Free flowing liquids generate static electricity which can produce a spark and ignite the solvent.
Large quantities of flammable liquids must be handled in areas free of ignition sources (including spark emitting motors and equipment) using non-sparking tools. Remember that vapors are heavier than air and can travel to a distant source of ignition.
Never heat flammable substances with an open flame. Instead use any of the following heat sources: steam baths, water baths, oil baths, heating mantles or hot air baths.
Do not distill flammable substances under reduced pressure.
Store flammable substances away from ignition sources. The preferred storage location is in flammable storage cabinets. If no flammable storage cabinet is available store these substances in a cabinet under the hood or bench. Five-gallon containers should only be stored in flammable storage cabinets. You can also keep small amounts of flammable liquids inside the hood for a short period of time. Storage in chemical fume hoods is not preferred because it reduces hood performance by obstructing airflow.
The volume of flammable liquids dispensed in small containers (not including safety cans) in the open areas of laboratories should not exceed one gallon. Never store glass containers of flammable liquids on the floor.
Oxidizing and corrosive materials should not be stored in close proximity to flammable liquids.
Flammable liquids should not be stored or chilled in domestic refrigerators and freezers but in units specifically designed for this purpose.
If flammable liquids will be placed in ovens make sure the ovens are appropriately designed for flammable liquids (no internal ignition sources and/or vented mechanically).
Highly reactive chemicals include those which are inherently unstable and susceptible to rapid decomposition as well as chemicals which, under specific conditions, can react alone, or with other substances in a violent uncontrolled manner, liberating heat, toxic gases, or leading to an explosion. Reaction rates almost always increase dramatically as the temperature increases. Therefore, if heat evolved from a reaction is not dissipated, the reaction can accelerate out of control and possibly result in injuries or costly accidents.
Air, light, heat, mechanical shock (when struck, vibrated or otherwise agitated), water, and certain catalysts can cause decomposition of some highly reactive chemicals, and initiate an explosive reaction. Hydrogen and chlorine react explosively in the presence of light. Alkali metals, such as sodium, potassium and lithium, react violently with water liberating hydrogen gas. Examples of shock sensitive materials include acetylides, azides, organic nitrates, nitro compounds, and peroxides.
Organic peroxides are a special class of compounds that have unusual stability problems, making them among the most hazardous substances normally handled in the laboratories. As a class, organic peroxides are low powered explosives. Organic peroxides are extremely sensitive to light, heat, shock, sparks, and other forms of accidental ignition; as well as to strong oxidizing and reducing materials. All organic peroxides are highly flammable.
Peroxide formers can form peroxides during storage and especially after exposure to the air (once opened).Peroxide forming substances include: aldehydes, ethers (especially cyclic ethers such as dioxane or tetrahydrofuran), compounds containing benzylic hydrogen - atoms, compounds containing the allylic structure (including most alkenes), vinyl and vinylidine compounds.
Examples of shock sensitive chemicals, high-energy oxidizers and substances that can form explosive peroxides are listed at the end of Section 3.
Before working with a highly reactive material or high-energy oxidizer, review available reference literature to obtain specific safety information. The proposed reactions should be discussed with your supervisor. Always minimize the amount of material involved in the experiment; the smallest amount sufficient to achieve the desired result should be used. Scaleups should be handled with great care, giving consideration to the reaction vessel size and cooling, heating, stirring and equilibration rates.
Excessive amounts of highly reactive compounds must not be purchased, synthesized, or stored in the laboratories. The key to safely handling reactive chemicals is to keep their quantities as small as possible and to keep them isolated from the substances that initiate their violent reactions. Unused peroxides must not be returned to the original container.
Do not work alone. All operations where highly reactive and explosive chemicals are used should be performed during the normal workday or when other employees are available either in the same laboratory or in the immediate area.
Perform all manipulations of highly reactive or high-energy oxidizers in a chemical fume hood. (Some factors to be considered in judging the adequacy of the hood include its size in relation to the reaction and required equipment, the ability to fully dose the sash, and the composition of the sash.)
Make sure that the reaction equipment is properly secured. Reaction vessels should be supported from beneath with tripods or lab jacks. Use shields or guards which are damped or secured.
If possible use remote controls for controlling the reaction (including cooling, heating and stirring controls).These should be located either outside the hood or at least outside the shield.
Handle shock sensitive substances gently, avoid friction, grinding, and all forms of impact.. Glass containers that have screw cap lids or glass stoppers should not be used. Polyethylene bottles that have screw-cap lids may be used. Handle water-sensitive compounds away from water sources. Light-sensitive chemicals should be used in light-tight containers. Handle highly reactive chemicals away from the direct light, open flames, and other sources of heat. Oxidizing agents should only be heated with fiberglass heating mantles or sand baths.
High-energy oxidizers, such as perchloric add, should only be handled in a wash down hood if the oxidizer will volatilize and potentially condense in the ventilation system. Inorganic oxidizers such as perchloric acid react violently with most organic materials.
When working with highly reactive compounds and high-energy oxidizers always wear the following personal protection equipment: lab coats, gloves and protective goggles. During the reaction, a face shield long enough to give throat protection should be worn.
Labels on peroxide forming substances should contain the date the container was received, first opened and the initials of the person who first opened the container. They should be checked for the presence of peroxides before using, and quarterly while in storage (peroxide test strips are available).If peroxides are found, the materials should be decontaminated, if possible, or disposed of. The results of any testing should be placed on the container label. If there is any sign of visible crystal formation around the bottle cap or at the bottom of a liquid peroxide forming substance, do not attempt to open the bottle or shake or transport it. Notify the Chemical Safety Coordinator at once to arrange for safe disposal of the material. Never distill substances contaminated with peroxides. Peroxide forming substances that have been opened for more than one year should be discarded. Never use a metal spatula with peroxides. Contamination by metals can lead to explosive decompositions.
Store highly reactive chemicals and high-energy oxidizers in closed cabinets segregated from the materials with which they react and, if possible, in secondary containers. You can also store them in the cabinet under a hood. Do not store these substances above eye level or on open shelves.
Store peroxides and peroxide forming compounds at the lowest possible temperature. If you use a refrigerator make sure it is appropriately designed for the storage of flammable substances. Store light-sensitive compounds in the light-tight containers. Store water-sensitive compounds away from water sources.
Shock sensitive materials should be discarded as hazardous waste after one year if in a sealed container and within six months of opening unless an inhibitor was added by the manufacturer.
Shock sensitive refers to the susceptibility of a chemical to decompose rapidly or explode when struck, vibrated or otherwise agitated. The following are examples of materials which can be shock sensitive:
|Acetylides of heavy metals||Hexanite||Organic nitramines|
|Aluminum ophrite explosive||Hexanitrodiphenylamine||Organic peroxides|
|Ammonium nitrate||Hydrazinium nitrate||Picratol|
|Ammonium perchlorate||Hyrazoic acid||Picric acid|
|Ammonium picrate||Lead azide||Picryl chloride|
|Calcium nitrate||Lead mannite||Polynitro aliphatic compounds|
|Copper Acetylide||Lead mononitroresorcinate||Potassium nitroaminotetrazole|
|Cyanuric triazide||Lead picrate||Silver acetylide|
|Cyclotrimethylenetrinitramine||Lead salts||Silver azide|
|Dinitroethyleneurea||Lead styphnate||Silver styphnate|
|Dinitroglycerine||Magnesium ophorite||Silver tetrazene|
|Dinitrophenolates||Mercury oxalate||Sodium amatol|
|Dinitrophenyl hydrazine||Mercury tartrate||Sodium dinitro-orthocresolate|
|Dipicryl sulfone||Nitrated carbohydrates||Tetrazene|
|Erythritol tetranitrate||Nitrated polyhydric alcohol||Tetrytol|
|Fulminate of mercury||Nitrogen trichloride||Trinitroanisole|
|Fulminate of silver||Nitrogen tri-iodide||Trinitrobenzene|
|Fulminating gold||Nitroglycerin||Trinitrobenzoic acid|
|Gelatinized nitrocellulose||Nitronium Perchlorate||Trirtitrophenetol|
|Guanyl nitrosaminoguanylidene hydrazine||Nitronium Perchlorate||Trinitroresorcinol|
|Guanyl nitrosamino guanyl-tetrazene||Nitrourea||Tritonal|
|Heavy metal azides||Organic amine nitrates||Urea nitrate|
The following are examples of materials which are powerful oxidizing reagents:
|Ammonium perchlorate||Dibenzoyl peroxide||Potassium perchlorate|
|Ammonium permanganate||Fluorine||Potassium peroxide|
|Barium peroxide||Hydrogen peroxide||Propyl nitrate|
|Bromine||Magnesium perchlorate||Sodium chlorate|
|Calcium chlorate||Nitric acid||Sodium chlorite|
|Calcium hypochlorite||Nitrogen peroxide||Sodium perchlorate|
|Chlorine trifluoride||Perchloric acid||Sodium peroxide|
|Chromium anhydride||Potassium bromate|
|Chromic acid||Potassium chlorate|
The following are examples of materials commonly used in laboratories which may form explosive peroxides.
|Acetal||Diethylene glycol||Sodium azide|
|Diacetlyene||Divinyl acetylene||Vinyl ethers|
|Dicyclopentadiene||Isopropyl ether||Vinylidene chloride|
|Diethyl ether||Methyl acetylene|
Compressed gases are unique in that they represent both a physical and a potential chemical hazard (depending on the particular gas).Gases contained in cylinders may be from any of the hazard classes described in this section (flammable, reactive, corrosive, or toxic).Because of their physical state (gaseous), concentrations in the laboratory can increase instantaneously if leaks develop at the regulator or piping systems, creating the potential for a toxic chemical exposure or a fire/explosion hazard. Often there is little or no indication that leaks have or are occurring. Finally, the large amount of potential energy resulting from compression of the gas makes a compressed gas cylinder a potential rocket or fragmentation bomb if the tank or valve is physically broken.
The contents of any compressed gas cylinder should be clearly identified. No cylinder should be accepted for use that does not legibly identify its contents by name. Color-coding is not a reliable means of identification and labels on caps have no value as caps are interchangeable.
Carefully read the label before using or storing compressed gas. The MSDS will provide any special hazard information.
Transport gas cylinders in carts one or two at a time only while they are secured and capped. All gas cylinders should be capped and secured when stored. Use suitable racks, straps, chains or stands to support cylinders. All cylinders, full or empty, must be restrained and kept away from heat sources. Store as few cylinders as possible in your laboratory. Return empty or unneeded cylinders to the supplier as quickly as possible.
Use only Compressed Gas Association standard combinations of valves and fittings for compressed gas installations. Always use the correct pressure regulator. Do not use a regulator adapter.
All gas lines leading from a compressed gas supply should be clearly labeled identifying the gas and laboratory served.
Place gas cylinders in such a way that the cylinder valve is accessible at all times. The main cylinder valve should be closed as soon as the gas flow is no longer needed. Do not store gas cylinders with pressure on the regulator. Use the wrenches or other tools provided by the cylinder supplier to open a valve if available. Never use pliers to open a cylinder valve.
Use soapy water to detect leaks. Never use a candle or match flame. Leak test the regulator, piping system and other couplings after performing maintenance or modifications which could affect integrity of the system.
Oil or grease on the high-pressure side of an oxygen cylinder can cause an explosion. Do not lubricate an oxygen regulator or use a fuel/gas regulator on an oxygen cylinder.
Never bleed a cylinder completely empty. Leave a slight pressure to keep contaminants out (172 kPa or 25 psi). Empty cylinders should not be refilled in the laboratories.
All gas cylinders should be clearly marked with appropriate tags indicating whether they are in use, full, or empty. Empty and full cylinders should not be stored in the same place.
Cylinders of toxic, flammable or reactive gases should be purchased in the smallest quantity possible and stored/used in a fume hood or under local exhaust ventilation. If at all possible avoid the purchase of lecture bottles. These cylinders are not returnable and it is extremely difficult and costly to dispose of them. Use the smallest returnable sized cylinder.
Wear safety goggles when handling any compressed gases.
Hydrogen gas has several unique properties, which make it potentially dangerous to work with. It has an extremely wide flammability range (LEL 4%, UEL 74.5%) making it easier to ignite than most other flammable gases. Unlike most other gases, hydrogen's temperature increases during expansion. If a cylinder valve is opened too quickly the heat or static charge generated by the escaping gas may cause it to ignite. Hydrogen burns with an invisible flame. Caution should therefore be exercised when approaching a suspected hydrogen flame. A piece of paper can be used to tell if the hydrogen is burning. Hydrogen embrittlement can weaken carbon steel. Therefore, cast iron pipes and fittings shall not be used. Those precautions associated with other flammable substances also apply to Hydrogen (see Section 3.1).
The major classes of corrosive chemicals are strong acids and bases, dehydrating agents, and oxidizing agents. These chemicals can erode the skin and the respiratory epithelium and are particularly damaging to the eyes. Inhalation of vapors or mists of these substances can cause severe bronchial irritation. If your skin is exposed to a corrosive, flush the exposed area with water for at least fifteen minutes. Then seek medical treatment.
Strong acids or concentrated acids can damage the skin and eyes and their burns are very painful. Nitric, chromic, and hydrofluoric acids are especially damaging because of the types of burns they inflict. Seek immediate medical treatment if you have been contaminated with these materials (particularly hydrofluoric acid, which can cause deep, initially painless bums and even cardiac arrest, if aggressive medial treatment is not given quickly).
Strong alkalis: The common strong bases used in the labs are potassium hydroxide, sodium hydroxide, and ammonia. Bums from these materials are often less painful than acids. However, damage may be more severe than acid bums because the injured person, feeling little pain, often does not take immediate action and the material is allowed to penetrate into the tissue. Ammonia is a severe bronchial irritant and should always be used in a well-ventilated area, if possible in a hood.
Dehydrating agents: This group of chemicals includes concentrated sulfuric acid, sodium hydroxide, phosphorous pentoxide, and calcium oxide. Because much heat is evolved on mixing these substances with water, mixing should always be done be adding the agent to water, and not the reverse, to avoid violent reaction and spattering. Because of their affinity for water, these substances cause severe burns on contact with skin. Affected areas should be washed promptly with large volumes of water.
Oxidizing agents: In addition to their corrosive properties, powerful oxidizing agents such as perchloric and chromic acids (sometimes used as cleaning solutions), present fire and explosion hazards on contact with organic compounds and other oxidizable substances. The hazards associated with the use of perchloric acid are especially severe. It should be handled only after thorough familiarization with recommended operating procedures (see section on reactives and high-energy oxidizers).
Corrosive chemicals should be used in the chemical fume hood, or over plastic trays when handled in bulk quantities (>1 liter) and when dispensing.
When working with bulk quantities of corrosives wear gloves, face shields, laboratory coats, and rubber aprons.
If you are handling bulk quantities on a regular basis, an eyewash should be immediately available and a shower close by. Spill materials - absorbent pillows, neutral absorbent materials or neutralizing materials (all commercially available) should be available in the laboratory.
Store corrosives in cabinets, under the hood or on low shelves, preferably in the impervious trays to separate them physically from other groups of chemicals. Keep containers not in use in storage areas and off bench tops.
If it is necessary to move bulk quantities from one laboratory to another or from the stockroom use a safety carrier (rubber bucket for secondary containment and protection of the container).
Substances that possess the characteristic of high acute toxicity can cause damage after a single or short-term exposure. The immediate toxic effects to human health range from irritation to illness and death. Hydrogen cyanide, phosgene, and nitrogen dioxide are examples of substances with high acute toxicity. The lethal oral dose for an average human adult for highly toxic substances range from one ounce to a few drops. The following procedures should be used when the oral LD, of a substance in the rat or mouse is less than 50 milligrams per kilogram body weight for solid materials or non-volatile liquids and 500 mg/kg body weight for volatile liquids or gases. Oral LD50 data for the rat or mouse is listed in the substance's MSDS. The LD50 toxicity test is usually the first toxicological test performed and is a good indicator of a substance's acute toxicity.
Substances that possess the characteristic of high chronic toxicity cause damage after repeated exposure or exposure over long periods of time. Health effects often do not become evident until after a long latency period - twenty to thirty years. Substances that are of high chronic toxicity may be toxic to specific organ systems - hepatotoxins, nephrotoxins, neurotoxins, toxic agents to the hematopoietic system and pulmonary tissue or carcinogens, reproductive toxins, mutagens, teratogens or sensitizers. The definition of each of these categories of toxic substances, and examples of substances, which fall into each of these different categories, can be found in Section 4 of this manual.
Specific acute and chronic toxicity information on the substances used in your laboratory can be found on the MSDS's of these substances. See Section 184.108.40.206 for information on how to obtain/locate MSDS's. If you have additional questions contact the Chemical Safety Coordinator.
Avoid or minimize contact with these chemicals be any route of exposure. Protect the hands and forearms by wearing gloves appropriate to the job and a laboratory coat rinse gloves prior to removing them.
Use these chemicals in a chemical fume hood or other appropriate containment device if the material is volatile or the procedure may generate aerosols (See guidelines for chemical fume hood use in Section 220.127.116.11). If a chemical fume hood is used it should be evaluated to confirm that it is performing adequately (a face velocity of at least 100 linear feet per minute (±20%)) with the sash at the operating height.
Store volatile chemicals of high acute or chronic toxicity in the cabinet under the hood or other vented area. Volatile chemicals should be stored in unbreakable primary or secondary containers or placed in chemically resistant trays (to contain spins).Nonvolatile chemicals should be stored in cabinets or in drawers. Do not store these chemicals on open shelves or counters.
Decontaminate working surfaces with wet paper towels after completing procedures. Place the towels in plastic bags and secure. Dispose of them in the normal trash unless they are obviously contaminated.
Volatile chemicals should be transported between laboratories in durable outer containers.
Vacuum pumps used in procedures should be protected from contamination with scrubbers or filters.
If one or more of these substances are used in large quantities, on a regular basis (three or more separate handling sessions per week), or for long periods of time (4-6 hours) a qualitative and potentially quantitative exposure assessment should be performed.
Lab personnel of childbearing age should be informed of any known male or female reproductive toxins used in the laboratory. An employee who is pregnant, or planning to become pregnant, and who is working with potential reproductive toxins that might affect the fetus, should contact the Chemical Safety Coordinator to evaluate her exposure and should inform her personal physician. The Chemical Safety Coordinator can assess potential exposures and work with the employee and laboratory supervisor, if necessary, to adjust work practices to minimize the potential risk.
This section establishes supplemental work procedures to control the handling of substances that are known to exhibit unusual acute or long-term chronic health hazards (carcinogens, reproductive toxins and highly acutely toxic substances). These unusually hazardous chemicals are listed as follow: Others may be added to the list as necessary.
Use these chemicals only in a chemical fume hood or other appropriate containment device (glove box).If a chemical fume hood is used it should be evaluated to confirm that it is performing adequately (a face velocity of at least 100 linear feet per minute (±20%) with the sash at the operating height.
Volatile chemicals should be stored in a vented storage area in an unbreakable, primary or secondary container or placed in a chemically resistant tray (to contain spills).Nonvolatile chemicals should be stored in cabinets or in drawers. Do not store these chemicals on open shelves or counters. Access to all of these chemicals should be restricted.
Volatile chemicals should be transported between laboratories in durable outer containers.
All procedures with these chemicals should be performed in designated areas. Other employees working in the area should be informed of the particular hazards associated with these substances and the appropriate precautions that are necessary for preventing exposures. All designated areas should be posted with a sign, which reads:
Vacuum pumps used in procedures should be protected from contamination with scrubbers or filters.
Analytical instruments or other laboratory equipment generating vapors and/or aerosols during their operation, should be locally exhausted or vented in a chemical fume hood.
Skin surfaces which might be exposed to these substances during routine operations or foreseeable accidents should be covered with appropriate protective clothing. Gloves should be worn whenever transferring or handling these substances. Consider using full body protection (disposable coveralls) if the potential for extensive personal contamination exists.
All protective equipment should be removed when leaving the designated area and decontaminated (washed) or, if disposable, placed in a plastic bag and secured. Call the Chemical Safety Coordinator for disposal instructions. Skin surfaces - hands, forearms, face and neck - should be washed immediately.
Work surfaces on which these substances will be handled should be covered with an easily decontaminated surface (such as stainless steel) or protected from contamination with plastic trays or plastic backed paper. Call the Chemical Safety Coordinator for decontamination and disposal procedures; these will be substance specific. Materials that will be disposed of should be placed in plastic bags and secured.
Chemical wastes from procedures using these substances should be placed in containers and disposed of as hazardous chemical waste. The wastes should be stored in the designated area (defined above) until picked up. If it is possible to safely chemically decontaminate all toxic substances to nontoxic materials during or at the end of the procedure this should be done.
Normal laboratory work should not be conducted in a designated area until it has been decontaminated or determined to be safe e by the laboratory supervisor or Chemical Safety Coordinator.
If one or more of these substances are used in large quantities, on a regular basis (three or more separate handling sessions per week), or for long periods of time (4-6 hours) a qualitative and potentially quantitative exposure assessment should be performed. Contact the Chemical Safety Coordinator to have this assessment performed. The Chemical Safety Coordinator in conjunction with the Department Chairman will determine if is appropriate to establish an ongoing medical surveillance program.
Lab personnel of childbearing age should be informed of any known male and female reproductive toxins used in the laboratory. An employee who is pregnant, or planning to become pregnant, and who is working with potential reproductive toxins that might affect the fetus, should contact the Chemical Safety Coordinator to evaluate her exposure and inform her personal physician. The Chemical Safety Coordinator can assess potential exposures and work with the employee and laboratory supervisor, if necessary, to adjust work practices to minimize the potential risk.