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7. Mechanical Safety
Typical machine shops have available (in working condition) drill presses, band saws, milling machines, lathes and others. In the use of all of these devices, eye protection is essential. Beware of any loose personal
articles (lab coat, ties, long hair) which may be caught on moving parts of equipment. On a lathe, the rotating positioning wheel can easily catch a pocket. Machine shop equipment is completely unforgiving and will
draw the body into it, tearing off fingers and limbs. Parts to be drilled or tapped should preferably be clamped down prior to use, or held down firmly. Otherwise the part may be lifted by the drill bit and turned
into a propeller blade. A block of sacrificial wood should be used to push parts through the band saw, not the fingers. In all cases, one needs to pay full attention to the equipment and not be distracted during
use. Tim Banks should be consulted for training before use of the equipment residing in the furnace room in MSE. Similarly for the use of the rolling mill, Dr. Sanders must be consulted.
The undergraduate mechanical testing area as well as the Mechanical Properties Research Laboratory (MPRL) are potentially hazardous areas where training and approval by R.C. Brown is required prior to use. Hazards
are related to the very high loads applied by the testing machines and the high power motors used to generate them. The Satec machine in the undergraduate area will generate 50,000 pounds of force on anything in its
path. For this reason, only one operator should have their hands between the pinch points (the cross head and the table) and this person should be the onlyone to start the machine. The machine should not be started
until the safety shields are in place and the area for testing is clear. The shields are essential since under certain conditions of fracture under load, parts could be sent flying at great velocities into the room.
With the Charpie machine, the hammer and anvil area are of greatest concern-the machine is capable of generating 250 ft-lbs of force (more force than a car's motor can generate, and on a small area.) The hammer must
be lifted and held in place by a small pin, which is then lever released. So that the lever is not released with another individual in the flight path of the hammer, only the operator should be behind the safety
barrier. The rolling mill will take anything fed into it and reduce its cross sectional area, including parts of the human body. For this reason, materials should be fed into the device with a push block, not
directly with the hands.
The MPRL is a particularly hazardous area and admittance to the facility is available only to those who have completed the MPRL training requirements. This area has 3000 psi hydraulic fluid driving the servo
controlled test frames. This fluid, if released in a fine jet, can cut through a steel plate. These machines are capable of generating 20,000 pounds of force at a rate of 10 m/s. A complete knowledge of the operator
controls and operating software is necessary for the machine to be operated safely.
8. Protective Clothing and Equipment
Eye protection must be worn at all times in all laboratories where other than purely instrumental studies are being conducted. Ordinary prescription glasses will not provide adequate protection from injury to the
eyes. The minimum acceptable protection are hardened glass or plastic safety glasses. Safety goggles or face shields should be utilized where there is a possibility of splashing chemicals, violent reactions or
flying particles. This is also the case in the MPRL where brittle materials may fracture. Specific goggles need to be worn for protection against laser hazards, and ultraviolet or other intense light sources.
Contact lenses should never be worn in the laboratory!
Skin contact is a potential route of exposure to toxic materials. Dermatitis, erythema, burns and absorption of toxic and/or carcinogenic chemicals are some of the consequences of exposing skin to hazardous liquids.
Therefore, proper protective gloves need to be worn when working with toxic or corrosive materials or with materials of unknown toxicity. No one glove is suitable for handling all chemicals. Gloves should be
selected on the basis of the material being handled and their suitability for the particular laboratory operation. Glove manufacturer's data (e.g. Fisher catalog) and the MSDS sheets for the chemicals provide useful
information in this regard. Chemical resistance is the most common type of glove evaluation. It is a qualitative and subjective rating and refers to the ability of the material to resist decomposition or
disintegration. It does not indicate the chemical protection afforded by the glove. Chemical permeation, on the other hand, does. Permeation is the process by which a hazardous liquid may pass through the glove
material to the inside. Because the glove material is not physically destroyed, the individual may not be aware that breakthrough has occurred and that he/she is being exposed. The period of adequate protection,
i.e., the breakthrough time plus some interval of time during chemical permeation, can only be determined by testing the glove with the chemical to be handled. When selecting gloves, determine which glove materials
have the longest breakthrough times and lowest penetration rates.
Solid toed shoes should be worn at all times. Open toed shoes or sandals offer little or no protection against chemical spills or broken glass. Avoid wearing loose (e.g., saris, dangling neckties, and over-large or
ragged laboratory coats), skimpy (e.g., shorts and/or halter tops), or torn clothing. If there is a possibility of contamination, personal clothing that will be worn home should be covered by protective apparel.
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9. Housekeeping
It is either learned up front, or with experience, neatness is required for all quality research. It is also a necessary safety precaution. Contamination of food, drink, and smoking materials are potential routes of
exposure to hazardous materials. For this reason, food or beverage should not be taken into any laboratory where there is a toxicity hazard. Glassware or utensils that have been used for laboratory operations should
never be utilized to prepare or consume food. Laboratory refrigerators and cold rooms should not be used for the storage of foods; separate, clearly labeled equipment should be employed. Smoking is prohibited in our
building. It is good practice to wash hands often, even when gloves are being utilized. Avoid the use of solvents for washing; they remove the natural protective oils from the skin and can cause irritation and
inflammation. In some cases, the solvents might even aid skin absorption of a toxic chemical.
Work areas need to be kept clean and free from obstructions. Cleanups should follow the completion of any operation or be done at the end of the day. Do not leave a disaster waiting for the next user. Aisles,
hallways and stairways must not be used for storage areas. Avoid storing heavy objects on high places from which they could fall. Do not store bottles or equipment on shelves on laboratory benches unless there are
restraining lips the shelves. Storage of bottles on benches is undesirable because of their propensity to be knocked over. Extended storage in hoods is also inadvisable because this practice interferes with the
airflow in the hood, clutters up the working space, and increases the amount of material that could become involved in a fire.
All reagents stored in other than their original containers must be labeled clearly as to the contents, date and name of the person storing the solutions. Do not label as ``Joe's solution'' since this is a
significant impediment to waste disposal at a later date. Chemicals stored in the laboratory should be inventoried periodically, and unneeded items should be disposed of. Containers should also be examined for
deteriorating labels. The quantity of chemicals stored in the laboratory should be kept as low as possible. Old or outdated solutions should be disposed of (see later section). Wastes needs to be placed in
appropriate receptacles properly labeled. Broken glassware, pipettes, syringes need to be placed first into puncture proof containers. The laboratory supervisor should arrange for the removal or safe storage of all
hazardous materials which personnel have on hand when they are about to terminate, graduate, or transfer.
10. Laboratory Equipment
Oil baths should always be monitored via a thermometer or other device to ensure that their temperature does not exceed the flash point of the oil being used. Smoking, caused by the decomposition of the oil or of
organic materials in the oil, represents another hazard. A laboratory worker using an oil bath heated above 100°C should be careful to guard against the possibility that water (or some other volatile substance)
could fall into the hot bath. Such an accident can splatter hot oil over a wide area. The oil bath should not be supported on an iron ring because of the possibility of accidental tipping.
The ordinary household refrigerator is not equipped with explosion-safe controls or door switches and should not be used to cool flammable liquids because sparks from controls or door switches may ignite the
vapor-air mixture. Explosion-safe refrigerators are constructed with its controls mounted outside the storage compartment. This type refrigerator is suitable for storing flammable liquids. An explosion-proof
refrigerator also has its controls mounted on the outside, but in addition, the controls are of an explosion-proof design. This type is needed only where both the internal and external environment present a fire or
explosion hazard. Every refrigerator should be clearly labeled to indicate whether or not it is suitable for storage of flammable liquids. Flammable liquids stored in a refrigerator must be in closed containers.
Laboratory refrigerators should not be used for storage of food or beverage unless used solely for that purpose and labeled as such.
Where (Bunsen) burners are used, distribute the heat with a wire gauze pad. Burners should not be left on when not in use. Workers should understand the hazards of burners before proceeding with an experiment.
Hand protection should be utilized when inserting glass tubing into stoppers or when placing rubber tubing on glass hose connections. To insert glass tubing, fire-polish the ends of the glass tubing; wet the glass
and stopper hole with glycerin or water; wrap a cloth around the glass; hold hands close together and rotate the glass back and forth. Never attempt to push the glass into the stopper or tubing. To remove glass
tubing and/or thermometers from stoppers: Lubricate the tubing with water or glycerin; wrap the tubing with a towel; gently twist the tubing, pulling lightly; if the tubing is stuck to the stopper, gently insert the
end of a rat-tailed file between the tubing and stopper, and rotate gently, while lubricating with glycerin. If this method fails, cut the stopper away.
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11. Cryogenics
Eye protection should be worn whenever cryogenic liquids are handled. Where splashing is a possibility, face shields should be used. Appropriate gloves, shoes, and clothing should be worn. In case of a splash,
immediately flood exposed areas and clothing with water. Avoid wearing watches, rings, bracelets, or other jewelry. Although many gases in the cryogenic range are not toxic (e.g. liquid nitrogen), they are all
capable of causing asphyxiation by displacing the air necessary to support life. Therefore, they should be used only in well-ventilated areas. Venting should be provided to avoid quick and violent pressure changes
when cryofluid vaporizes. Handle combustible cryogens such as liquid hydrogen and liquid natural gas in the same way combustible gases are handled: provide ventilation, keep away from open flames and other ignition
sources, prohibit smoking, and vent gases to a safe location. Exposed glass portions of the cryogenic container should be taped to minimize the flying glass hazard if the container should break or implode.
12. Chemical Safety
12.1 Predicting Outcomes of Experiments
The strong background given to MSE undergraduates in physical chemistry and thermodynamics should be exploited in predicting events which may occur in the laboratory. Using the fundamental laws developed in these
courses, tabulated data can be used to predict potentially dangerous vapor pressures, whether or not reactions will occur, and whether the heats of reactions will approach explosive behavior. Useful tabulations may
be found in the CRC Handbook of Chemistry and Physics, the JANAF thermochemical tables, and the North American Combustion Handbook. A few examples will be cited:
If we wish to melt copper in an evacuated and sealed fused silica ampoule, the vapor pressure of copper is negligible, and no dangerous pressures will build up. This is not true, however, for phosphorous, where as
can be seen in Figure , the vapor pressure builds up appreciably with increasing temperature. From a standard glass science textbook, the tensile strength of silica glass is roughly 50 MPa, or 490 atm, thus the
container will burst at 900°C, if not before. The figure was generated using the integrated form of the Clapeyron equation:
|
lnp = |
DH
R |
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æ
ç
è |
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1
T0 |
- |
1
T |
|
ö
÷
ø |
|
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Where p is the equilibrium vapor pressure formed over the condensed phase in a closed system, R is the gas constant, DH is the heat of vaporization or sublimation of the condensed phase (assumed to vary
insignficantly with temperature), T0 is the equilibrium boiling or sublimation temperature under atmospheric pressure, and T is temperature. For Figure , DH and T0 data were obtained from the CRC Handbook. In using
equations such as this, it is important to understand the nuances of the terms and how they relate to a realistic experimental situation. These nuances can often only be elucidated by following the derivation of the
expression and observing what simplifying or conditional assumptions were made.
The JANAF tables have very complete enthalpy and free energy tabulations. To predict whether a reaction will occur, the standard state Gibbs energy equation is useful:
where DG° is the standard state free energy change for a reaction, and kp is the equilibrium constant. For a equilibria
the value of DG° may be obtained from the standard state Gibbs energies of formation (products - reactants, each one multiplied by its stoichiometry constant) in the JANAF tables. The equilibrium constant for
such a reaction is the ratio of product and reactant activities:
If gases are assumed ideal, the activities can be written as the pressure of the reaction constituent divided by its pressure in its standard state. For gases, the standard state is that it is pure and at one
atmosphere. For condensed phases, the standard state requirement is simply that it is pure (thus the copper in brass is not in its standard state). Thus for all pure condensed phases, their activity is unity. As an
example, consider what would happen if flowing CO2 atmosphere were used in a graphite furnace chamber. The equilibrium constant for CO2 + C = 2CO may be written:
Using tabulated data, this ratio is plotted as a function of temperature in Figure .
Figure 1: (left) Vapor pressures predicted by the integrated Clayperon equation.
Figure 2: (right) Equilibrium
partial pressure ratio showing propensity of CO2 to react with graphite to form CO.
Clearly, around 800°C the carbon dioxide will react with the graphite chamber, making carbon monoxide. If the exit gas is vented into the room, the atmosphere in the room will be poisoned.
If a thermite reaction such as:
|
5Mg + TiO2 + B2O3 ®
5MgO + TiB2 |
|
is to be investigated, the standard state enthalpies of formation in the JANAF tables can be used to determine a standard state enthalphy of reaction at 298 K of -1093.6 kJ/mol. The heat content tabulations on
the same pages can be used to show that this reaction under adiabatic conditions will result in a product temperature of 2387°C. This certainly dictates the use of a highly refractory container for this reaction as
well as other safety precautions.
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12.2 Chemical Spills
Chemical spills can be handled effectively if some pre-planning has been conducted. Individuals should become familiar with proper clean-up procedures before a spill occurs. Commercial spill kits are available
(chemistry stores) that have instructions, absorbents, reactants and protective equipment. Common examples: dolomite will neutralize HF. A sulfur-based mixture is used on mercury spills to form a compound with a
much lower vapor pressure. A vacuum line, needle-nose pipette, and trap can be used to draw up the spill. The MSDS for a particular chemical will provide specific information about neutralizing agents.
For flammable liquids, spark-producing equipment should be turned off. The spilled liquid should absorbed and the absorbing material should placed in a plastic bag and kept away sources of ignition. This material
should be disposed of in the same manner as hazardous chemical waste For toxic chemicals, all spark-producing equipment should be turned off, and all experiments shut down. The room should be evacuated until it is
decontaminated. Call the DESHS on (894-6224 or 894-4635) how to deal with a particular toxic spill. With acids or alkalis, do not neutralize spilled liquid unless you are sure that the resulting reaction will not
release hazardous fumes or cause explosion. Otherwise, neutralize the spilled liquid and absorb it. For a mercury spill, droplets and pools of mercury metal can be pushed together and then collected by suction using
an aspirator bottle with a long capillary tube or a vacuum device made from a filtering flask, a rubber stopper, and several pieces of flexible and glass tubing. Cover droplets of mercury in non-accessible crevices
with calcium polysulfide and excess sulfur. These will form compounds with the mercury with much lower vapor pressures. Dispose of this material in the same manner as hazardous chemical waste. For alkali metals,
smother the spill with a special dry powder extinguisher, and keep any and all moisture away from the spill.
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12.3 Chemical Fume Hoods
Chemical fume hoods are intended to remove vapors, gases, and dusts of toxic, flammable, corrosive or otherwise dangerous materials. With the sash lowered, laboratory fume hoods can also afford workers protection
from such hazards as chemical splashes or sprays and fires. However, they are not designed to withstand explosions. Before performing hazardous operations, make simple checks to determine that the hood is working
(e.g., a small piece of paper held at the face of the hood will be sucked inward). When work is being conducted within the hood, position the sash so that protection from splashes, flying debris, etc., is provided.
Normally, this is a 12-16 inch work opening. Experimental procedures should be conducted well inside the hood. Moving an apparatus 5-10 cm back from the front edge into the hood can reduce the vapor concentration at
the face by 90%. Hoods are not intended for the storage of chemicals. Materials stored in them should be kept to a minimum and in a manner that will not interfere with airflow. Hoods should be considered as backup
safety devices that can contain and exhaust toxic, offensive, or flammable materials. They should not be regarded as a means of disposing of chemicals.
The use of perchloric acid requires specially designed Perchloric Acid Fume Hoods. For the specifications of a Perchloric Acid Fume Hood, as well as the requirements and procedures for installation, repair, removal
and relocation, consult the Facilities Engineering Dept. or the DESHS.
12.4 Transporting Chemicals
Transporting chemicals may not only be dangerous to the individual undertaking the transport but to innocent bystanders unaware of the potential hazard. When chemicals are carried, they should be placed in a safety
container, acid-carrying bucket, or other appropriate container to protect against breakage and spillage. When they are transported on a wheeled cart, the cart should have wheels large enough to negotiate uneven
surfaces without tipping or stopping suddenly. Hazardous chemicals should be transported on freight elevators, wherever possible, so as to avoid exposure to persons on passenger elevators.
12.5 Flammable Liquids
Flammable substances are the most common hazardous materials found in the laboratory. The propensity to vaporize, ignite, burn or explode varies with the specific type or class of substance. An indicator of the
flammability of a solvent is its flash point, the lowest temperature at which a liquid gives off vapor in sufficient concentration to form an ignitable mixture with air. This information is usually available on the
label affixed to the chemical container or in MSDS. Flammable liquids are defined as those liquids which have flash points below 100°F (37.7°C). Combustible liquids have flash points between 100°F and 210°F
(93.3°C). The most hazardous liquids are those that have flash points at room temperature or lower, particularly if their range of flammability is broad. Flash points and flammability limits of some common chemicals
appear in Table .
Table 1: Critical parameters for some common laboratory chemicals. Class IA - Flash point below 730°F, boiling point below 1000°F. Class 1B - Flash point below 730°F, boiling point at or above 1000°F. Class 1C -
Flash point at or above 730°F, and below 1000°F.
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Flammable Limit |
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(percent by volume |
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Flash |
Boiling |
Ignition |
in air) |
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Point |
Point |
Temperature |
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Chemical |
Class |
(°C) |
(°C) |
(°C) |
Lower |
Upper |
|
Acetaldehyde |
1A |
-37.8 |
21.1 |
175.0 |
4.0 |
60.0 |
|
Acetone |
1B |
-17.8 |
56.7 |
465.0 |
2.6 |
12.8 |
|
Benzene |
1B |
-11.1 |
80.0 |
560.0 |
1.3 |
7.1 |
|
Carbon disulfide |
1B |
-30.0 |
46.1 |
80.0 |
1.3 |
50.0 |
|
Cyclohexane |
1B |
-20.0 |
81.7 |
245.0 |
1.3 |
8.0 |
|
Diethyl ether |
1A |
-45.0 |
35.0 |
160.0 |
1.9 |
36.0 |
|
Ethyl alcohol |
1B |
12.8 |
78.3 |
365.0 |
3.3 |
19.0 |
|
n-Heptane |
IB |
- 3.9 |
98.3 |
215.0 |
1.05 |
6.7 |
|
n-Hexane |
1B |
-21.7 |
68.9 |
225.0 |
1.1 |
7.5 |
|
Isopropyl alcohol |
1B |
11.7 |
82.8 |
398.9 |
2.0 |
12.0 |
|
methyl alcohol |
1B |
11.1 |
64.9 |
385.0 |
6.7 |
36.0 |
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Methyl ethyl ketone |
1B |
- 6.1 |
80.0 |
515.6 |
1.8 |
10.0 |
|
Pentane |
1A |
-40.0 |
36.1 |
260.0 |
1.5 |
7.8 |
|
Styrene |
1B |
32.2 |
146.1 |
490.0 |
1.1 |
6.1 |
|
Toluene |
1B |
4.4 |
110.6 |
480.0 |
1.2 |
7.1 |
|
p-Xylene |
1C |
27.2 |
138.3 |
530.0 |
1.1 |
7.0 |
For a fire to occur, three conditions must exist: a concentration of flammable vapor that is within the flammable limits of the substance; an oxidizing atmosphere, such as air; and a source of ignition. Elimination
of one of these three will prevent the start of fire or extinguish an existing fire. Air cannot usually be excluded. Therefore, the problem usually involves preventing the coexistence of flammable vapors and an
ignition source. Because spillage of a flammable liquid is always a possibility, strict control of ignition sources is important. The vapors of all flammable liquids are heavier than air, and capable of traveling
considerable distances. This possibility should be recognized of ignition sources at a lower level than that at which the substance is used.
"NO SMOKING" signs should be posted and obeyed wherever flammable liquids are handled or stored. Never smoke or use an open flame near flammable liquids. Flammables should not be heated with an open flame.
Some other type of heat source, such as a steam bath, water bath, or heating mantle should be used. Transfer flammable liquids with caution. The friction of flowing liquids may be sufficient to generate static
electricity which in turn may cause a spark and ignition. Therefore, ground or bond all such large containers before pouring from them. (The DESHS can provide the details of this procedure.). Flammable liquids
should be dispensed and used in a hood or well-ventilated area so that flammable vapors will not accumulate.
Keep only small quantities of flammable materials available for immediate use. An approved safety can with a self-closing cover, vent, and flame arrester is the best container for storing flammable liquids or waste
solvents in small quantities. An ordinary five-gallon container does not provide adequate protection in cases of fire. Refrigerators and cooling equipment used for storing flammable liquids should be explosion-safe
(see Section 10).
12.6 Toxic Substances
Toxicity is the capability of a chemical to produce injury. Almost any substance is toxic when taken in doses exceeding "tolerable" limits. Hazard is the probability that an injury will occur or rather the
prospect that an individual will receive a toxic dose. The effects of a toxic chemical may be qualified into several categories. Local toxicity is the effect a substance has on the body tissues at the point of
contact. Acute toxicity is the effect a substance has after only one or a few short, relatively large exposures. Chronic toxicity is the effect a substance has as a result of many small exposures over a long period
of time.
An individual may be exposed to a chemical substance via a number of different routes: inhalation ingestion, contact with skin or eyes. Inhalation of toxic vapors, mists, gases or dusts can result in poisoning by
absorption through the mucous membrane of the mouth, throat, and lungs, and can cause serious local effects. Because of the large surface area of the lung (90 square meters total surface) along with its continuous
blood flow, inhaled gases or vapor may be very rapidly absorbed and carried into the circulatory system. The rate of absorption will vary with the concentration of the toxic substance, its solubility and the
individual inhalation rate. The degree of injury from exposure to a toxic substance depends on the toxicity of the material, its solubility in tissue fluids and the concentration and duration of exposure.
Ingestion of chemicals used in the laboratory may result in significant injury. The relative acute toxicity of a chemical can be determined by its oral LD50, that quantity of material which, when ingested, will cause
the death of 50% of test animals. This LD50 is expressed usually in milligrams per kilogram of body weight. To prevent ingestion of chemicals, laboratory workers should wash their hands immediately after using a
toxic substance and before leaving the laboratory. Food and drink should not be stored or consumed in areas where chemicals are being used. Chemicals should not be tasted, and pipetting and siphoning of liquids
should never be done by mouth.
Skin contact is the most frequent route of exposure to chemical substances. A common result of skin contact is localized irritation, but some materials can be absorbed through the skin sufficiently to produce
systemic poisoning. Contact of most chemicals with the eyes will result in pain and irritation. A considerable number of chemical substances are capable of causing burns or loss of vision. Alkaline materials,
phenols and strong acids are particularly corrosive and may cause permanent loss of vision. Furthermore, the vascular network of the eyes may permit the rapid absorption of many chemicals.
Before initiating work with a chemical substance, the researcher or laboratory worker should be familiar with the types of toxicity, the toxic dose, and the hazards of the chemical. It is also important to realize
that two or more substances may act synergistically to produce a toxic effect than that of either substance alone. Furthermore, chemical reactions involving two or more substances may form products significantly
more toxic than the starting materials. Therefore, the entire experimental procedure should be evaluated.
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12.7 Commonly Used Chemicals
The most common laboratory solvent sequence is trichloroethylene (TCE), acetone, methanol, and deionized water. Note that in particular trichloroethylene is a known carcinogen, and should be handled with extra
caution. Some individuals are sensitive to darkroom chemicals (developer, fixer, stop bath), resulting in contact dermatitis. Tongs should be used to move photographic paper through these chemicals.
12.8 Corrosives
Corrosives consist of four major classes: Strong acids, strong bases, dehydrating agents and oxidizing agents. Inhalation of the vapors of these substances can cause severe bronchial irritation. These chemicals erode
the skin and the respiratory epithelium, and are particularly damaging to the eyes. Acids and alkalis should be stored separately in a cool ventilated area, away from metals, flammables, and oxidizing materials. The
storage area should be checked regularly for spills and leaks, and there should be suitable spill cleanup materials available. Protective clothing should be worn whenever acids or alkalis are handled.
Always pour acids into water, never the reverse. Cap bottles securely and store them securely, but do not store acids and alkalis together. Clean up spills promptly. Do not leave residues on a bottle or lab bench
where another person may come in contact with them. Wear protective garb when handling acids or alkalis. This includes rubber gloves, apron, and eye protection.
Four acids deserve special attention because of the
hazards they pose. These are: nitric acid, perchloric acid, picric acid, and hydrofluoric acid.
Nitric acid
is corrosive and its oxides are highly toxic. Because nitric acid is also an oxidizing agent, it may form flammable and explosive compounds with many materials (e.g.,
ethers, acetone and combustible materials). Paper used to wipe up nitric acid may ignite spontaneously when dry. Nitric acid should be used only in a hood, and should be stored away from combustible materials.
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Perchloric acid
(HClO4) forms highly explosive and unstable compounds with many organic compound and even with metals. Unstable perchlorate compounds may collect in the duct work of
fume hoods and cause fire or violent explosions. Therefore, perchloric acid should be used with extreme caution and only in a fume hood designed for its use-a perchloric acid hood having corrosion-resistant duct
work and washdown facilities. We have no such facilities in our school. Minimum quantities of perchloric acid should be kept on hand, and the container stored in a perchloric acid hood on a glass tray that is deep
enough to hold the contents of the bottle. Perchloric acid should not be kept for more than one year since explosive crystals may form. A number of graduate students at universities have had their fingers blown off
when unscrewing the cap from perchloric acid. Liquid residue forms a crust on the bottle and cap threads, which explode when the next user attempts to open the bottle. Similar explosions occurred when attempting to
clean non-perchloric acid fume hoods, where vapors formed crystals in the crevices in the hood and duct work. Perchloric acid should be stored in an explosion proof refrigerator since it may become unstable at room
temperature.
Picric acid
can form explosive compounds with many combustible materials. When the moisture content decreases, picric acid may become unstable and may explode from being shaken. Picric
acid should be dated, stored away from combustible materials, and not kept for extend periods (i.e., longer than one year).
Hydrofluoric acid
is extremely corrosive and will even attack glass. All
forms-dilute, concentrated solutions or the vapor-can cause serious burns. HF does not produce overt tissue burns like most acids; instead, it diffuses through tissue and will dissolve bone. Burns from hydrofluoric
acid heal slowly and with great difficulty. Therefore, hydrofluoric acid should be used in suitable fume hood while gloves, safety glass and lab coat are being worn. Inhalation of HF mists or vapor will cause
serious respiratory tract irritation that may be fatal. Care should taken to avoid contacting hydrofluoric acid with metals or ammonia since toxic fumes may result.
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12.9 Metals
Alkali metals (e.g., sodium and potassium) react violently with water and decompose the water, giving off hydrogen, which may be ignited by the heat of reaction. This is similarly true for alkaline earth metals
(calcium and magnesium). Alkali metals can also ignite spontaneously in air, especially when the metal is in powdered form, and/or the air is moist. Alkali metals should be stored under mineral oil or kerosene.
Avoid using oils containing sulfur since a hazardous reaction may occur. Use only special, dry powder fire extinguishers on alkali metal fires. Any waste alkali metals should be placed in labeled, leak-proof
container, covered with mineral oil and disposed of via the DESHS. Finely powdered metals (e.g. Al or Fe) that come in contact with acids may ignite and burn. Metal powders can also create a dust explosion hazard
when the powders become airborne in an area where a spark or flame is present.
Mercury is a virulent poison and is readily absorbed through the respiratory tract, the gastrointestial tract, or through unbroken
skin. It is therefore imperative that it not be touched, or its vapors inhaled. It acts as a cumulative poison (like arsenic) since only small amounts of the element can be eliminated at a time by the human
organism. The vapor pressure of mercury is quite high; air saturated with mercury vapor at 20°C contains a concentration that exceeds the toxic limit more than 100 times. Therefore mercury should only be used in a
well-ventilated hood. Mercury spills must be immediately covered with sulfur to bring down the vapor pressure (see section 12.2).
12.10 Highly Reactive Chemicals and Explosives
When chemical reactions are considered safe, it is generally because the reaction rate is relatively slow or can be easily controlled. Certain reactions proceed, however, at such a fast rate and generate so much
heat, that they may result in explosion. Care should be taken to ensure there is sufficient cooling and surface area for heat exchange.
Many chemical reactions may involve hazards like those mentioned above, but
can be handled safely if some preliminary planning has been done. Planning an experiment should include knowledge of the reactivity, flammability, and toxicity of the chemicals used in and produced by the
experiment. This information may be obtained from the MSDS data base, using the Handbook of Reactive Chemical Hazards (L. Bretherck), or by calling the DESHS (4-4635). Such planning shall include selection of the
proper safety procedures, clothing and equipment as well as consideration of the possibility of a power failure, equipment breakdown, or fire, and the precautions that can be taken to minimize the consequences.
12.11 Specific Chemicals
Organic peroxides are a class of compounds that have unusual stability problems that make them among the most hazardous substances handled in laboratories. As a class, organic peroxides are considered to be powerful
explosives. They are sensitive to heat, friction, impact, and light as well as to strong oxidizing and reducing agents. All organic peroxides are flammable. Types of compounds known to form peroxides are listed in
Table
Table 2: Common compounds that form peroxides during storage.
|
|
|
Ethyl ether |
Isopropyl ether |
|
Tetrahydrofuran |
Divinyl acetylene |
|
Dioxane |
Vinylidene chloride |
|
Acetal |
Potassium metal |
|
Methy i-butyl ketone |
Sodium amide |
|
Ethelyene glycol dimethl ether (glyme) |
Butadine |
|
Vinyl ethers |
Tetrafluoroethylene |
|
Dicyclopentadiene |
Vinyl acetylene |
|
Methyl acetylene |
Vinyl acetate |
|
Cumene |
Vinyl chloride |
|
Tetrahydronaphthalene |
Vinyl pyridine |
|
Cyclohexene |
Chlorobutadiene |
|
Methylcyclopentane |
Butandiene |
All peroxidizable materials should be stored in a cool place, away from light. Metal cans are preferable; do not store ethers in ground stoppered bottles. Ethers and peroxidizable materials should be ordered
only in small quantities, and should be dated upon receipt and when opened. They should be discarded within a year after receipt if unopened, or within months of opening. Ethers should always be handled in a hood to
assure proper ventilation. This will protect individuals from inhaling the vapors and prevent accumulation of explosive concentrations of the vapor. For methods of peroxide detection and removal, consult the DESHS.
Certain combinations of chemicals are particularly dangerous and should be avoided. Table indicates the compatibility of various chemicals.
Table 3: Examples of incompatible chemicals
|
|
|
Chemical |
Is Incompatible With |
|
|
|
Hydrofluoric acid |
Ammonia (aqueous or anhydrous) |
|
(anhydrous) |
|
|
Hydrogen peroxide |
Copper, chromium, iron, most metals or their salts, |
|
alkochols, acetone, organic materials, aniline, |
|
nitromethane, combustible materials |
|
Hydrogen sulfide |
Fuming nitric acid, oxidizing gases |
|
Hypochlorites |
Acids, activated carbon |
|
Iodine |
Acetylene, ammonia (aqueous or anhydrous), hydrogen |
|
Mercury |
Acetylene, fulminic acid, ammonia |
|
Nitrates |
Acids |
|
Nitroparaffins |
Inorganic bases, amines |
|
Oxalic acid |
Silver, mercury |
|
Oxygen |
Oils, grease, hydrogen, flammable liquids, solids, or gases |
|
Perchloric acid |
Acetic anhydride, bismuth and its alloys, alcohol, |
|
paper, wood, grease, oils |
|
Peroxides, organic |
Acids (organic or mineral), avoid friction, store cold |
|
Phosphorus (white) |
Air, oxygen, alkalis, reducing agents |
|
Potassium |
Carbon tetrachloride |
|
Potassium chlorate |
Sulfuric and other acids |
|
Potassium perchlorate |
Sulfuric and other acids |
|
(see also chlorates) |
|
|
Potassium permanganate |
Glycerol, ethylene glycol, benzaldehyde, sulfuric acid |
|
Selenides |
Reducing agents |
|
Silver |
Acetylene, oxalic acid, tartartic acid, ammonium |
|
compounds, fulminic acid |
|
Sodium |
Carbon tetrachloride, carbon dioxide, water |
|
Sodium nitrate |
Ammonium nitrate and other ammonium salts |
|
Sodium peroxide |
Ethyl or methyl alcohol, glacial acetic acid, acetic |
|
anhydride, benzaldehyde, carbon disulfide, glycerin, |
|
ethylene glycol, ethyl acetate, methyl acetate, furfural |
|
Sulfides |
Acids |
|
Sulfuric acid |
Potassium chlorate, potassium perchlorate, potassium |
|
permaganate (similar compounds of light metals, |
|
such as sodium, lithium) |
|
Tellurides |
Reducing agents |
Other chemical hazards that may result explosions or fires include:
Acetylenic compounds
are explosive in mixture 2.5-80% with air. At pressures of 2 or more atmospheres, acetylene (C2H2) subjected to electrical discharge or high temperature decomposes with explosive
violence. Dry acetylides detonate on receiving the slightest shock.
Aluminum chloride
(AlCl3) should be considered a potentially dangerous material. If moisture is present, there may be sufficient
decomposition to build up a considerable pressure of HCl.
Ammonia
reacts with iodine to form nitrogen triiodide, which is explosive, and hypochlorites to form chlorine.
Benzoyl peroxide
when dry, is easily ignited and sensitive to shock. It decomposes spontaneously at temperatures above 50°C
Carbon disulfide
is both very toxic and very flammable; mixed with air, its vapors can be
ignited by a steam bath or pipe, a hot plate, or a glowing light bulb.
Chlorine
may react violently with hydrogen or with hydrocarbons when exposed to sunlight.
Chromium trioxide-pyridine
complex (CrO3-C5H5N) may explode if the CrO3 concentration is too high. The complex should be prepared by addition of CrO3 to excess C5H5N.
Diazomethane
(CH2N2) and related compounds should be treated
with extreme caution. They are very toxic, and the pure gases and liquids explode readily. Solutions in ether are safer from this standpoint.
Dimethyl sulfoxide
(CH3)2SO] decomposes violently on contact
with a wide variety of active halogen compounds. Explosions from contact with active metal hydrides have been reported. Its toxicity is still unknown, but it does penetrate and carry dissolved substances through the
skin membrane.
Dry ice
should not be kept in a container that is not designed to withstand pressure. Containers of other substances stored over dry ice for extended periods generally absorb carbon
dioxide (CO2) unless they have been sealed with care. When such containers are removed from storage, and allowed to come rapidly to room temperature, the CO2 may develop sufficient pressure to burst the container
with explosive violence. On removal such containers from storage, the stopper should be loosened, or the container itself should be wrapped in towels and kept behind a shield. Dry ice can produce serious burns.
Drying agents
“Ascarite'' should not be mixed with phosphorus pentoxide (P2O5) because the mixture may explode if it is warmed with a trace of water. Because the cobalt salts used as moisture indicators in
some drying agents may be extracted by some organic solvents, the use of these drying agents should be restricted to gases.
Diethyl, diisopropyl, and other ethers
sometimes explode during heating or
refluxing because of the presence of peroxides. Ferrous salts or sodium bisulfite can be used to decompose the peroxides, and passage over basic active alumina will remove most of the peroxidic material. In general,
however, old samples of ethers should be discarded.
Ethylene oxide
(C2H4O) has been known to explode when heated in a closed vessel. Experiments using ethylene oxide under pressure should be carried out
behind suitable barricades.
Halogenated Compounds
Chloroform (CHCl3), carbon tetrachloride (CCl4), and other halogenated solvents should not be dried with sodium, potassium, or other active metal;
violent explosions are usually the result of such attempts. Many halogenated compounds are toxic.
Hydrogen peroxide
(H202) Stronger than three percent can be dangerous; in contact with the skin, it may
cause severe burns. Thirty percent H2O2 may decompose violently if contaminated with iron, copper, chromium, or other metals or their salts.
Liquid-nitrogen-cooled traps
open to the atmosphere rapidly
condense liquid from the air. Then, when the coolant is removed, an explosive pressure buildup occurs, usually with enough force to shatter glass equipment. Hence, only sealed or evacuated equipment should be so
cooled.
Lithium aluminum hydride
(LiAlH4) should not be used to dry inethyl ethers or tetrahydrofuran; fires from this are very common. The products of its reaction with CO2 have been reported to be
explosive. Carbon dioxide or bicarbonate extinguishers should not be used against LiAlH4 fires, which should be smothered with sand or some other inert substance.
Ozone
(O3) is a highly reactive and
toxic gas. It is formed by the action of ultraviolet light on oxygen (air) and, therefore, certain ultraviolet sources may require venting to an exhaust hood.
Palladium or platinum on carbon, platinum oxide, Raney nickel, and other catalysts
should be filtered from catalytic hydrogenation reaction mixtures carefully. The recovered catalyst is usually saturated with
hydrogen and highly reactive and, thus, will inflame spontaneously to exposure to air. Particularly in large-scale reactions, the filter cake should not be allowed to become dry. The funnel containing the still
moist catalyst filter cake should be put into water bath immediately after completion of the filtration. Another hazard in working with such catalysts is the danger of explosion if an additional catalyst is added to
a flask in which hydrogen is present.
Parr bombs
used for hydrogenations have been known to explode. They should be handled with care behind shields, and the operator should wear goggles.
Perchlorates
The use of perchlorates should be avoided wherever possible. Perchlorates should not be used as drying agents if there is possibility of contact with organic compounds in proximity to a
dehydrating acid strong enough to concentrate the perchloric acid (HClO4) more than 70% strength (e.g., in a drying train that has a bubble counter containing sulfuric acid). Safer drying agents should be used.
Seventy percent HClO4 can be boiled safely approximately 200°C, but contact of the boiling undiluted acid or the hot vapor with organic matter, or even easily oxidized inorganic matter (such as compounds of
trivalent antimony), will lead to serious explosions. Oxidizable substances must never be allowed to contact HClO4. Beaker tongs, rather than rubber gloves should be used when handling fuming HClO4. Perchloric acid
evaporations should be carried out only in fume hoods designed specifically for this purpose.
Permanganates
are explosive when treated with sulfuric acid. When both compounds are used in an absorption
train, an empty trap should be placed between them.
Peroxides
(inorganic)-when mixed combustible materials, barium, sodium, potassium peroxides form explosives that ignite easily.
Phosphorus
(P) (red and white) forms explosive mixtures with oxidizing agents. White P should be stored under water because it is spontaneously flammable in air. The reaction of P with aqueous hydroxides gives phosphine,
which may ignite spontaneously in air or explode.
Phosphorus trichloride
(PCl3) reacts with water to form phosphoric acid, which decomposes on heating to form phosphine, which may ignite spontaneously
or explode. Care should be taken in opening containers of PCl3, and samples that have been exposed to moisture should not be heated without adequate shielding to protect the operator.
Potassium
(K) is
in general more reactive than sodium. It ignites quickly on exposure to humid air and, therefore, should be handled under the surface of a hydrocarbon solvent such as mineral oil or toluene (see Sodium).
Residues from vacuum distillations
(for example, ethyl palmitate) have been known to explode when the still was vented to the air before the residue was cool. Such explosions can be avoided by venting the
still pot with nitrogen, by cooling it before venting, or by restoring the pressure slowly.
Sodium
(Na) should be stored in a closed container under kerosene, toluene, or mineral oil. Scraps of Na or K
should be destroyed by reaction with n-butyl alcohol. Contact with water should be avoided because Na reacts violently with water to form H2 with evolution of sufficient heat to cause ignition. Neither carbon
dioxide nor bicarbonate fire extinguishers should be used on alkali metal fires.
Sodium azide
may react violently with benzoyl chloride plus potassium hydroxide, bromine, carbon disulfide, chromium
oxychloride, copper, lead, nitric acid, dimethylsulfate and ibromomalonitrile. It is especially important that sodium azide not be allowed to come in contact with heavy metals (for example, by being poured into a
lead or copper drain) or their salts; heavy metal azides detonate with notorious ease.
Sulfuric acid
(H2SO4) should be avoided, if possible, as a drying agent in desiccators. If it must be used, glass
beads should be placed in it to help prevent splashing when the desiccator is moved. The use of H2SO4 in melting point baths should be avoided (silicone oil should be used). To dilute H2SO4, add the acid slowly to
cold water.
Trichloroethylene
(Cl2CCHCl) reacts under a variety of conditions with potassium or sodium hydroxide to form dichloroacetylene, which ignites spontaneously in air and detonates readily even
at dry-ice temperatures. The compound itself is highly carcinogenic, and precautions should be taken decreasing solvent.
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13. Handling of Chemical Waste
Each laboratory/activity should conduct at least an annual survey and dispose of unneeded/expired material. At the end of any project or prior to the departure of an individual, all material should be clearly
identified and unneeded/expired material disposed of. To the extent feasible, waste should be segregated and not combined. Mixing of different type wastes poses dangers and imposes cost penalties on the University
for waste disposal.
Waste containers need to be compatible with the waste collected, kept closed unless material is being added, capable of being transported, and appropriately labeled. Do not use containers over 5 gallons (20 liters)
without prior consultation with the DESHS. Containers which have been emptied using normal practices, e.g., pouring, are not considered hazardous except for poisons; these containers should never be reused, and are
considered hazardous even when empty.
Waste collection containers must be clearly labeled with: 1. The word "WASTE" in a conspicuous location. 2. The type waste being accumulated in the container, e.g., ``oil, halogenated solvent, hydrochloric
acid." Before the waste is picked-up by the DESHS, the following must be on the label: 1. The name and phone number of an individual who can answer questions concerning the waste. 2. The actual contents of the
container - provide chemical names not abbreviations, process descriptions, or brand/product names. Labels are available on request from the DESHS. Sharp materials (``sharps") must be placed in special puncture
resistant containers. Sharps include needles, scalpels, test tubes, pipettes, petri dishes, and anything that can potentially pierce a plastic bag.
The DESHS is responsible for picking up hazardous chemical waste from individual activities. Activities desiring a waste pick-up will notify DESHS with the type, amount, location, and contact person phone number.
They will, in most cases, respond to telephone requests. Written requests are preferred, and in the case of certain activities, may be required. Arrangements may be made for periodic pick-ups of waste without
individual requests or for consolidation of waste from a number of activities at one site. Direct questions to the Hazardous Waste Officer, Department of Environmental Science, Health, and Safety at 894-6224 or
894-4635.
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14. Emergency Call List
The Institute Department of Environmental Science, Health, and Safety should be called with any and all safety concerns: Examples: suspect toxic gases, unidentified vapors or odors, chemical spills, biological
hazards, asbestos hazards, radon hazards, water or soil contamination, or any situation that may require analysis. Unless life or property are in imminent danger, do not call the Atlanta fire department or Atlanta
Hazardous Materials Team. An assessment will be made by the Georgia Tech DESHS, and they will make the decision. Individuals of this department can be reached, day or night. Attempt to contact personnel in the
following order:
Environmental Compliance Officer
Office: 404-894-6119
Hazardous Waste Officer
Office: 404-894-6224
Environmental Safety Maintenance Technician
Office: 404-894-6128
Research Scientist
Office: 404-894-9381
Fire Safety Coordinator
Office: 404-894-2990
The Department of Environmental Science, Health and Safety is not responsible for radiation hazards. In case of a radiation hazard contact Dr. Rod Ice at the Neely Nuclear Research Center at 404-894-3600.
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