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VII. Chemicals: Managing, Handling and
Disposing Maintaining chemical safety
requires care in ordering, storing, using, and disposing of chemicals.
Chemical safety is the responsibility of everyone who uses the classroom
laboratory, but safe management of chemicals begins with the teacher who
orders and uses these products.
Safe management of chemicals in the
classroom requires that the teacher have adequate knowledge of the chemicals
to be used and their interactions. Information about these chemicals is
available on the Materials Safety Data Sheets (MSDSs) for each chemical, in
chemical catalogues, and on container labels. An Internet search under the
keyword "MSDS" will yield information on websites that supply information
on chemicals. •See Appendix C, MSDS:
Explanation and Samples. Before making a request to use a
reagent chemical not on the school system’s approved list, the teacher should
read and research the appropriate MSDS to determine whether the chemical can
be safely used with students. The teacher also should consider -- ·
the relative hazard
level of the chemical. ·
the educational
value of using the chemical. ·
the teacher’s
experience or lack of experience in using the substance. ·
the degree to which
the laboratory is equipped for the safe use of the chemical. •See Chapter III.E,
Ventilation. 1. Selecting Reagent
Chemicals Each
school system should develop a list of reagents acceptable for use in the
various science courses. A teacher who wishes to use a substance not on the
appropriate list must seek the permission of the science supervisor by
submitting a written request. The request should include the following: a. A copy of the
lesson plan for the proposed demonstration or laboratory exercise. b. Information
supporting the following assertions: ·
Use of the substance is pedagogically sound. ·
The demonstration or laboratory exercise using the substance
is an effective way to illustrate an important property, process or concept. ·
No satisfactory substitute for the substance is readily
available. ·
Adequate safeguards are in place to ensure proper use of the
substance. ·
Students will be instructed in the proper handling of the
substance (as indicated in the lesson plan). a. Information on
the following to enable the supervisor to make an informed decision: ·
the extent of
exposure of students and the teacher to the chemical (including estimate of
time to the nearest minute). ·
the age or maturity
level of the students who will be exposed. b. In considering a
substance for use in the laboratory, teachers are advised to check hazardous
materials lists available in print and on the Internet. Resources available
include the following: ·
The National Toxicological Program for lists of carcinogenic
and reproductive toxins (teratogens and mutagens) ·
The National Research Council’s Prudent Practices in the
Laboratory (1995), Chapter 3, for lists of carcinogens, mutagens,
teratogens, and highly flammable materials ·
The Oak Ridge Toxicology Information Resources Center’s Catalog
of Teratogenic Agents Appearance of a substance on one of
these lists does not preclude its appropriate use in the school laboratory.
The dose makes the difference. Even common substances such as water and salt
can be toxic in excessive quantities. Many substances that are toxic at some
levels can safely be used at lower levels. Materials
Safety Data Sheets (MSDSs), which provide information on toxicity levels, may
be found on the Internet. •See
Appendix H, Resources. 2. Ordering Reagent
Chemicals a. Before ordering
reagent chemicals, the teacher should - ·
make sure the
chemical is on the school system’s list of approved chemicals. ·
be capable of
assessing the hazards of chemicals. ·
be sufficiently
knowledgeable to recognize requests from other teachers for nonessential
chemicals. ·
have a current
inventory of existing chemicals. •See
Chapter VII.A.3, Chemical Inventory. b. Reagent chemicals
should be ordered in quantities consistent with the rate of use. c. Reagent chemicals
should be ordered in polyethylene bottles or plastic-coated bottles, if
available, to minimize breakage, corrosion, and rust. d. For each reagent
chemical used, ask the following questions: ·
Can proper storage be provided for the chemical? ·
Are the facilities appropriate for the use of the chemical? ·
Will the chemical or its end products require disposal as
hazardous waste? ·
Is appropriate personal protective equipment available for
safe use of the chemical or its end product? ·
Have persons who will handle and use the chemical been trained
in handling reagent chemicals? Are they aware of the hazards? 3. Chemical
Inventory Inventories
of reagents are essential in the control of chemical hazards. They enable members
of the science department to determine the existence of a specific reagent
chemical, its location, and its approximate shelf age. A reagent chemical
inventory should be conducted at least once a year. The chemical inventory
record should - ·
contain the date the
inventory was conducted. ·
identify chemical
reagents by name and formula. ·
specify the amount of
each reagent present. ·
indicate the storage
location of each reagent. ·
indicate the hazard of
each reagent, using information from the Material Data Safety Sheet (MSDS)
for each substance and the appropriate National Fire Protection Association
hazard code. •See
Appendix E, NFPA Identification Codes, and Appendix C, Materials Data Safety
Sheets (MSDS): Explanation and Samples. The following
website offers more information on this topic: ·
indicate the arrival date
and quantity of all reagents received. The following
website offers more information on this topic: 1. Chemical Storage a. General
Guidelines ·
Secure storage areas against unauthorized removal of chemicals
by students or others. ·
Protect the school environment by restricting emissions from
stored reagent chemicals. Vents should be ducted to the outside. ·
Where possible, storage areas should have two separate exits. ·
Maintain clear access to and from the storage areas. ·
Do not store chemicals in aisles or stairwells, on desks or
laboratory benches, on floors or in hallways, or in fume hoods. ·
Use NFPA- or OSHA-approved storage cabinets for flammable
chemicals. ·
Use an appropriate "Acid Cabinet" for any acid
solutions of 6 M concentration or higher. Nitric acid needs to be isolated. ·
Use refrigerators of explosion-proof or explosion-safe design
only. Do not use standard refrigerators to store flammable chemicals. Place NO
FOOD labels on refrigerators used to store chemicals. ·
Label storage areas with a general hazard symbol to identify
hazardous chemicals and indicate correct fire fighting
procedures. •See
Appendix E, NFPA Hazard Codes. ·
File a Material Safety Data Sheet (MSDS) for every chemical
stored in the laboratory. ·
Store all reagent chemicals in compatible family groups. Do
not alphabetize. •See
Appendix F, Storage of Chemicals. ·
Store all chemicals at eye level and below. The preferred
shelving material is wood treated with polyurethane or a similar impervious
material. All shelving should have a two-inch lip. If you use shelving with
metal brackets, inspect the clips and brackets annually for corrosion and
replace as needed. ·
Store chemical reagents prepared in the laboratory in plastic
bottles (if possible and appropriate to the chemical) to minimize the risk of
breakage. ·
Date containers upon receipt and again when opened. ·
Attach chemical labels with all necessary information to all
containers. •See
Chapter VII.A.5, Labeling of Stored Reagent Chemicals. ·
When opening newly received reagent chemicals, immediately
read the warning labels to be aware of any special storage precautions such
as refrigeration or inert atmosphere storage. ·
Test peroxide-forming substances periodically for peroxide
levels; dispose of these substances after three months unless the MSDS for
the substance indicates a longer shelf life. •See
Appendix G, Hazards of Peroxide-Forming Substances, and Appendix C, Materials
Data Safety Sheets (MSDS): Explanation and Samples. ·
Check chemical containers periodically for rust, corrosion,
and leakage. ·
Store bottles of especially hazardous and moisture-absorbing
chemicals in chemical-safe bags. ·
Maintain a complete inventory in the room where the chemicals
are stored, and make a copy available to fire fighters. ·
Keep storage areas clean and orderly at all times. ·
Have spill cleanup supplies (absorbents, neutralizers) in any
room where chemicals are stored or used. b. Storage of
Flammable and Combustible Liquids
i. Definitions Flash
point is defined as the
minimum temperature of a liquid at which it gives off sufficient vapor to
form an ignitable mixture with air. Flammable
liquid is defined as any liquid
that has a flash point below 100 F (37.8°C). Combustible
liquid is defined as any
liquid that has a flash point at or above 100 F (37.8 ° C).
ii. Guidelines ·
Limit the amount of flammable and combustible materials stored
to that required for one year of laboratory work. ·
Use only NFPA- or OSHA-approved metal flammables cabinets to
store flammable and combustible liquids. Label the cabinets FLAMMABLE -
KEEP AWAY FROM FIRE. The
following website offers more information on this topic: ·
When possible, store flammable and combustible liquids in
their original containers or safety cans. A safety can is an approved
container of not more than 5 gallons (18.9 L) capacity. The container should
have a spring-closed spout cover and an integral flame-arrester and be
designed to relieve internal pressure safely when exposed to fire. The
following website offers more information on this topic: c. Storage of
Compressed Gases
·
Use small lecture-bottle-type gas cylinders only. Store all
gas cylinders in an upright position.
·
Store gas cylinders in a cool dry place away from corrosive
chemicals or fumes.
·
Store gas cylinders away from highly flammable substances.
·
When cylinders are no longer in use, shut the valves, relieve
the pressure in the gas regulators, removed the regulators, and cap the
cylinders.
·
Label empty gas cylinders EMPTY or MT.
·
Store empty gas cylinders separately from full gas cylinders.
·
Store flammable or toxic gases at or above ground level - not
in basements.
·
Use cylinders of toxic, flammable, or reactive gases in fume hoods
only.
·
When moving cylinders, be sure the valve cap is securely in
place to protect the valve stem and valve. Do not use the valve cap as a
lifting lug.
·
If large gas cylinders are used, they should be chained. A hand
truck should be available for transporting them to and from the storage area. 1. Labeling of
Stored Reagent Chemicals Proper
labeling is fundamental to a safe and effective laboratory operation.
Reagents created in the laboratory also require labeling. a. Purchased Reagent
Chemicals All
purchased reagent chemicals should be labeled with -
·
chemical name.
·
date received.
·
date of initial
opening.
·
shelf-life.
·
hazard warnings. •See
Appendix E, NFPA Identification Codes.
·
storage classification
location.
·
name and address of
manufacturer. b. Solutions All
reagents created in the laboratory should be labeled with -
·
chemical name and
formula.
·
concentration.
·
date prepared.
·
name of person who
prepared the reagent.
·
storage classification.
·
hazard warning label
(available from a safety supplier).
·
reference to original
source of chemical (e.g., manufacturer, which jar, etc.). 1. Dispensing
Reagent Chemicals The MSDS
for an individual substance should always be consulted before a chemical is
used for any reason. It is the best source of information about possible
hazards, spill procedures, handling procedures and first aid for any
substance. Teachers
are responsible for instructing their students about safe methods for working
with chemicals. a. Safety Guidelines
for Dispensing Reagent Chemicals ·
Use the smallest amount of the chemical possible in any
experiment. Microscale experiments should be
considered. ·
Consider distributing the amount of chemical for an experiment
into vials for each student. This minimizes waste and can save time during
the class period. ·
Use proper containers for dispensing solids and liquids.
Solids should be contained in wide-mouthed bottles and liquids in containers
that have drip-proof lips. ·
Label all containers properly. ·
Never return dispensed chemicals to stock bottle, as it
inevitably results in contamination despite your best precautions. a. Dispensing
Flammable Liquids When a
liquid flows from one container to another, static electricity can build up
in one of the containers. If this charge becomes large enough, a spark will
be produced between the containers, and a flammable liquid may be ignited.
This is particularly a danger when the liquid is stored in a large container
and distributed to smaller containers. Such
containers should be bonded and grounded: ·
Bonding refers to providing an electrical
connection between the two containers. Commonly this is accomplished by attaching
a wire, fastening one end each to the two containers. ·
Grounding refers to connecting one of the
containers (usually the stationary one) to a grounding source such as a
metallic water pipe. 2. Common Hazards Four
categories of hazards commonly found in school laboratories are: corrosives,
flammables, oxidizers/reactives, and toxins. In
this section, mercury is discussed separately as a special hazard. a. Corrosives Corrosives
are materials that can injure body tissue or cause corrosion of metal by
direct chemical action. Major classes of corrosive substances are: ·
strong acids (e.g., sulfuric, nitric, hydrochloric and
hydrofluoric acids) ·
strong bases (e.g., sodium hydroxide and potassium hydroxide) ·
dehydrating agents (e.g., sulfuric acid, sodium hydroxide,
phosphorus pentoxide, and calcium oxide) ·
oxidizing agents (e.g., hydrogen peroxide, chlorine, and
bromine) b. Flammables Flammable
substances have the potential to catch fire readily and burn in air. A
flammable liquid itself does not catch fire; it is the vapors produced by the
liquid that burn. Important properties of flammable liquids: ·
Flash point is the minimum temperature of a liquid at which
sufficient vapor is given off to form an ignitable mixture with air. ·
Ignition temperature is the minimum temperature required to
initiate self-sustained combustion independent of a heat source. •See
Chapter VII.A.4.b, Storage of Flammable and Combustible Liquids. c. Oxidizers/Reactives Oxidizers/reactives include chemicals that can explode, violently
polymerize, form explosive peroxides, or react violently with water or
atmospheric oxygen.
i. Oxidizers: An oxidizing
agent is any material that initiates or promotes combustion in other
materials, either by causing fire itself or by releasing oxygen or other
combustible gases.
ii. Reactives: Reactives
include materials that are pyrophoric ("flammable solids"), are
water reactive, form explosive peroxides, or may undergo such reactions as
violent polymerization. a. Toxins A toxic
substance is one that, even in small amounts, can injure living tissue.
i. Methods of Toxins
Entering the Body: ·
Ingestion - Absorption through the digestive
tract. This process can occur through eating with contaminated hands or in
contaminated areas. ·
Absorption - Absorption through the skin
often causes dermatitis. Some toxins that are absorbed through the skin or
eyes can damage the liver, kidney, or other organs. ·
Inhalation - Absorption through the
respiratory tract (lungs) through breathing. This process is the most
important route in terms of severity. ·
Injection - Percutaneous injection of a
toxic substance through the skin. This process can occur in the handling of
sharp-edged pieces of broken glass apparatus and through misuse of sharp
materials such as hypodermic needles.
ii. Types of Toxins OSHA
defines a hazardous chemical as any chemical that is a physical or a health
hazard (CFR 1910.1200). Many chemicals can cause toxic effects in the body.
Below are some classes of toxic chemicals. Information about these chemicals
is available on the MSDS for each chemical, in chemical catalogues, on
container labels, and on several Internet sources. The
following website offers more information on this topic: The
following website offers more information on this topic: ·
Irritants are noncorrosive chemicals that
cause reversible inflammatory effects (swelling and redness) on living tissue
by chemical action at the site of contact. Because a wide variety of organic
and inorganic chemicals are irritants, skin and eye contact with all
chemicals in the laboratory should be avoided. ·
Corrosive substances are solids, liquids, and gases
that cause destruction of living tissue by chemical action at the site of
contact. ·
Allergens are substances which cause an
adverse reaction by the immune system. As these reactions result from
previous sensitization from the substance or similar substance, chemical
allergens will be different for each person. ·
Asphyxiants are substances
that interfere with the transport of an adequate supply of oxygen to the
vital organs of the body. They can do this by either displacing oxygen from
the air or by combining with hemoglobin and thus reducing the blood’s ability
to transport oxygen. ·
Carcinogens are cancer-causing substances
listed in the Annual Report on Carcinogens. Many substances known or
suspected to be carcinogenic are still found to be in high school laboratories.
There is little reason for most of them to be there; they should be disposed
of as quickly as possible. ·
Reproductive & developmental toxins (teratogens and
mutagens) either have an adverse effect on the various aspects of reproduction
(fertility, gestation, lactation and general reproductive performance) or act
during pregnancy to cause adverse effects on the embryo or fetus. ·
Neurotoxins induce an adverse effect on the
structure or function of the central and/or peripheral nervous system. These
effects can be permanent or reversible. ·
Toxins affecting other organs can also be a
hazard. Most of the chlorinated hydrocarbons and aromatic compounds, some
metals, carbon monoxide, cyanides, and others can produce one or more effects
on target organs in the body. a. Mercury Mercury
and its compounds, both organic and inorganic, are health hazards. Metallic
mercury has a measurable vapor pressure, and the production of vapor is
accentuated by heating the mercury or subdividing as occurs in a spill.
Laboratory sources of mercury include, among others, thermometers, manometers
(barometers), and batteries. Not only is the vapor harmful, but the metal
itself is absorbable through the intact skin.
i. Mercury and its
compounds should never be found in the elementary or middle school.
ii. In high schools,
mercury should be used only under special circumstances. Mercury is
acceptable in high school only if all four of these criteria are met: ·
No substitute is available that will provide the degree of
accuracy required for the operation. ·
The teacher has obtained prior approval from the science
supervisor. ·
All persons in the laboratory working with mercury or an
instrument containing mercury wear chemical splash safety goggles, full face
shields, aprons, and adequate clothing to prevent skin contact. ·
Access to mercury or any instrument containing the element is
restricted by keeping source and instrument under lock and key except when in
use. 3. Spill Cleanup a. General Notes on
Chemical Spills
·
Spills should be contained, the area cleared of students, and
the spill cleaned up immediately.
·
Waste from spill cleanup should be disposed of appropriately. •See
Chapter VII.C, Chemical Waste Strategies.
·
After floor spill has been thoroughly cleaned up in the
appropriate manner, the area should be mopped dry to minimize the risk of
slipping and falling. a. Spills that
Constitute Fire Hazard
·
Extinguish all flames immediately.
·
Shut down all experiments.
·
Vacate the room until the situation has been corrected. b. Other Spills
i. Use an absorbent
material to neutralize the liquids. Materials include: ·
for acids, powdered sodium bicarbonate ·
for bromine, sodium thiosulfate solution (5-10%) or limewater ·
for organic acids, halides, nonmetallic compounds, or
inorganic acids, use slaked lime and soda ash ·
or general spills, use commercial absorbents or spill kits,
small particles of clay absorbents (kitty litter), or vermiculite
ii. Wear rubber
gloves and use a dustpan and brush. Clean the area thoroughly with soap and
water, then mop dry.
iii. Aromatic amine,
carbon disulfide, ether, nitrile, nitro compound, and organic halide spills
should be absorbed with cloths, paper towels, or vermiculite and disposed of
in suitably closed containers. 1. Mercury Spills Whenever
possible, mercury should not be used in school laboratories. If and when it
is used, however, there is a chance of a spill occurring. Each laboratory
should therefore be equipped with a specialized, commercially available,
mercury-spill kit. Follow the directions found in your kit for cleaning up a
mercury spill. All laboratory work with
chemicals eventually produces chemical waste. Everyone associated with the
science laboratory shares the legal and moral responsibility to minimize the
amount of waste produced and to dispose of chemical waste in a way that has
the least impact on the environment. Depending on what is contained in the
waste, some waste must be professionally incinerated or deposited in
designated landfills, while other waste can be neutralized or discharged in
normal streams. 1. Minimizing Waste a. Alternative
Substances Whenever
possible, use less toxic substances in place of the more toxic chemicals to
minimize the hazards and disposal costs associated with using certain
chemicals. The table below contains a list of suggested substitutions for
some toxic chemicals.
b. Microscale Laboratories Microscale
experiments reduce the amount of material required, therefore reducing the
hazards encountered and disposal costs. Many laboratory manuals on the market
describe microscale experiments. These should be
considered whenever possible to replace "classic" laboratory
experiments. c. Classroom
Demonstrations Another
way to reduce the hazards for students, and reduce the amount of waste
generated, is for the teacher to perform classroom demonstrations for the more
hazardous experiments rather than have each student carry out the experiment.
d. Coordinate
Laboratory Work When
planning laboratory experiments, try to coordinate with co-workers who may be
doing the same or similar experiments so that reagents are made up at one
time in the building, thus minimizing the amount of "left-over"
reagent at the end of the experiment. 2. Waste Storage
Prior to Disposal a. All waste should be
stored in properly labeled containers. The label should contain the date,
type of waste, and any other pertinent information required by the disposal
company. b. Waste should be
segregated to avoid unwanted reactions and to allow for cost-effective disposal.
c. Waste should be
stored in closed containers except when additional waste is being added. d. Each school
science department should maintain a central, secure waste storage area. 3. Disposing of
Waste Teachers
should be aware of the appropriate method of disposal for any chemical used
in the school laboratory. When in doubt, refer to the MSDS, a disposal
manual, or the source of the chemical. a. Classification of
Hazardous Waste The
Environmental Protection Agency classifies wastes as: ·
Ignitable: has a flash point below 140°C, is
an oxidizer, or is an ignitable compressed gas. ·
Corrosive: has a pH equal to or below 2.0 or
a pH equal to or greater than 12.5. ·
Reactive: is reactive with air or water, is
explosive, or is cyanide or sulfide. ·
Toxic: has certain
levels of certain metals, solvents, or pesticides greater than
prescribed limits. ·
Others: any chemical found in the lists in 40 CFR 261 subpart
D. a. Classroom
Management ·
Make disposal options a part of all laboratory instructions
for students. For each chemical waste produced, instruct students as to the
appropriate disposal, including disposing of the substance in a disposal
container or down the drain. •See
Chapter VII.C.3.c, Drain Disposal. ·
Place all laboratory waste in a properly labeled container.
The label should contain the date and type of waste. ·
Immediately following the laboratory activity, place the waste
containers in a secure location until the containers can be removed to the central
storage area. ·
Some chemical wastes may be recycled. Teachers should seek
guidance on recycling from local safety officers or other knowledgeable
administrative staff. b. Drain Disposal ·
Before considering drain disposal, be certain that the sewer
flows to a wastewater treatment plant and not to a stream or other natural
water course. Check with the local waste water treatment plant authority
to determine what substances are acceptable for drain disposal. ·
Any substance from a laboratory should be flushed with at
least 100 times its own volume of tap water. ·
Acids and bases should be at least above pH 3 and below pH 8
before being placed in a sanitary drain. ·
If both ions of a compound are on the following lists, that
compound may be placed in a sanitary drain:
·
The following organic compounds can go into a drain:
·
For additional information on drain disposal of substances,
see the National Research Council’s Prudent Practices in the Laboratory
(1983). ·
The
following website offers more information on this topic: ·
If in doubt about the proper disposal of a chemical, check
with the local safety officer or refer to Flinn or
a similar reference. c. Compounds Not
Suitable for Drain Disposal For compounds
not suitable for drain disposal, label and package the compound and ship by a
shipper approved by the U.S. Department of Transportation to a landfill
designated by EPA to receive chemical and hazardous waste. Even though
packed, shipped, and disposed of by licensed and approved firms, generators
of hazardous waste are responsible for the wastes. |
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