SECTION 7: Safe Work Practices and Procedures

• 7A General Work Practices
• 7B Flammable Materials
• 7C Peroxide Forming Compounds and Reactives
• 7D Corrosives
• 7E Compressed Gases
• 7F Cryogenics
• 7G Electrical Safety
• 7H Pressure and Vacuum Systems
• 7I Laboratory Equipment
• 7J Particularly Hazardous Materials

7A: General Work Practices

• Before You Begin
• Chemical Storage
• Personal Behavior
• Transporting Chemicals
• Working with Scaled-Up Reactions
• Unattended Experiments
• Working Alone

Before You Begin (top)

Every laboratory worker should observe the following rules:

1. Know the potential hazards and appropriate safety precautions before beginning work. Ask and be able to answer the following questions:
   • What are the hazards?
   • What are the worst things that could happen?
   • What do I need to do to be prepared?
   • What work practices, facilities or personal protective equipment are needed to minimize the risk?
2. Know the location and how to use emergency equipment, including safety showers and eyewash stations.
3. Never block safety equipment or doors and keep aisles clear and free from tripping hazards.
4. Familiarize yourself with the emergency response procedures, facility alarms and building evacuation routes.
5. Know the types of personal protective equipment available and how to use them for each procedure.
6. Be alert to unsafe conditions and actions and bring them to the attention of your supervisor or lab manager immediately so that corrections can be made as soon as possible.
7. Prevent pollution by following waste disposal procedures. Chemical reactions may require traps or scrubbing devices to prevent the release of toxic substances to the laboratory or to the environment.
8. Position and clamp reaction apparatus thoughtfully in order to permit manipulation without the need to move the apparatus until the entire reaction is completed. Combine reagents in the appropriate order and avoid adding solids to hot liquids.

Chemical Storage (top)

Many local, state and federal regulations have specific requirements that affect the handling and storage of chemicals in laboratories.

General Considerations

In general, store materials and equipment in cabinets and on shelving provided for such storage.

• Avoid storing materials and equipment on top of cabinets. If you must place things there, however, you must maintain a clearance of at least 18 inches from the sprinkler heads or (if no sprinkler heads are present) 24 inches from the ceiling.
• Be sure that the weight of the chemicals does not exceed the load capacity of the shelf or cabinet. Some incidents where shelving or a cabinet collapsed due to overload are described in Anecdotes.
• Wall-mounted shelving must have heavy-duty brackets and standards. This type of shelving is not recommended for chemical storage.
• Cabinets for chemical storage must be of solid, sturdy construction, preferably hardwood or metal.
• Do not store materials on top of high cabinets where they will be hard to see or reach.
• Do not store corrosive liquids above eye level.
• Provide a specific storage location for each type of chemical, and return the chemicals to those locations after each use.
• Avoid storing chemicals in the workspace within a laboratory hood, except for those chemicals currently in use.
• If a chemical does not require a ventilated cabinet, store it inside a closable cabinet or on a shelf that has a lip to prevent containers from sliding off in the event of an accident or fire.
• Do not expose chemicals to heat or direct sunlight.
• Observe all precautions regarding the storage of incompatible chemicals.
• Use corrosion resistant storage trays or secondary containers to collect materials if the primary container breaks or leaks.
• Distinguish between refrigerators used for chemical storage and refrigerators used for food storage. Each refrigerator should be labeled "No Food" or "Food Only". Labels are available from EHS by calling 8-5294.
• Do not store flammable liquids in a refrigerator unless it is approved for such storage. Such refrigerators are designed with non-sparking components to avoid an explosion.
• Chemical storage cabinets located outside the laboratory (e.g., in hallways) should be labeled with the name of the laboratory group that owns and uses it.

Segregation of Chemicals

Incompatible chemicals should not be stored together. Storing chemicals alphabetically, without regard to compatibility, can increase the risk of a hazardous reaction, especially in the event of container breakage. In addition to the Chemical Compatibility Chart below, there are several resources available, both in print and on-line, including the National Oceanic and Atmospheric Administration Chemical Reactivity Worksheet.

Use common sense when setting up chemical storage. Segregation that disrupts normal workflow can increase the potential for spills.

There are several possible storage plans for segregation. In general, dry reagents, liquids and compressed gases should be stored separately, then by hazard class, then alphabetically (if desired).

Segregate dry reagents as follows:

• Oxidizing salts
• Flammable solids
• Water-reactive solids
• All other solids

Segregate liquids as follows:

• Acids
  • Separate mineral acids (hydrochloric, sulfuric) from organic acids (picric, acetic)
• Bases
• Oxidizers
• Perchlorates
• Flammable or combustible liquids
• All other liquids

Segregate compressed gases as follows:

• Toxic gases
• Flammable gases
• Oxidizing and inert gases

Chemical Incompatibility Chart

Mixing these chemicals purposely or as a result of a spill can result in heat, fire, explosion, and/or toxic gases.  This is a partial list.

 

Acetic Acid	Chromic Acid, nitric acid, hydroxyl-containing compounds, ethylene glycol, perchloric acid, peroxides, and permanganates.
Acetone	Bromine, chlorine, nitric acid, sulfuric acid, and hydrogen peroxide.
Acetylene	Bromine, chlorine, copper, mercury, fluorine, iodine, and silver.
Alkaline and Alkaline Earth Metals such as calcium, lithium, magnesium, sodium, potassium, powdered aluminum	Carbon dioxide, carbon tetrachloride and other chlorinated hydrocarbons, water, Bromine, chlorine, fluorine, and iodine.  Do not use CO2, water or dry chemical extinguishers.  Use Class D extinguisher (e.g., Met-L-X) or dry sand.
Aluminum and its Alloys (especially powders)	Acid or alkaline solutions, ammonium persulfate and water, chlorates, chlorinated compounds, nitrates, and organic compounds in nitrate/nitrate salt baths.
Ammonia (anhydrous)	Bromine, chlorine, calcium hypochlorite, hydrofluoric acid, iodine, mercury, and silver.
Ammonium Nitrate	Acids, metal powders, flammable liquids, chlorates, nitrates, sulfur and finely divided organics or other combustibles.
Aniline	Hydrogen peroxide or nitric acid.
Bromine	Acetone, acetylene, ammonia, benzene, butadiene, butane and other petroleum gases, hydrogen, finely divided metals, sodium carbide, turpentine.
Calcium Oxide	Water
Carbon (activated)	Calcium hypochlorite, all oxidizing agents.
Caustic (soda)	Acids (organic and inorganic).
Chlorates or Perchlorates	Acids, aluminum, ammonium salts, cyanides, phosphorous, metal powders, oxidizable organics or other combustibles, sugar, sulfides, and sulfur.
Chlorine	Acetone, acetylene, ammonia, benzene, butadiene, butane and other petroleum gases, hydrogen, finely divided metals, sodium carbide, turpentine.
Chlorine Dioxide	Ammonia, methane, phosphine, hydrogen sulfide.
Chromic Acid	Acetic acid, naphthalene, camphor, alcohol, glycerine, turpentine and other flammable liquids.
Copper	Acetylene, hydrogen peroxide.
Cumene Hydroperoxide	Acids
Cyanides	Acids
Flammable Liquids	Ammonium nitrate, chromic acid, hydrogen peroxide, nitric acid, sodium peroxide, bromine, chlorine, fluorine, iodine.
Fluorine	Isolate from everything.
Hydrazine	Hydrogen peroxide, nitric acid, and other oxiding agents.
Hydrocarbons	Bromine, chlorine, chromic acid, fluorine, hydrogen peroxide, and sodium peroxide.
Hydrocyanic Acid	Nitric acid, alkali.
Hydrofluoric Acid	Ammonia, aqueous or anhydrous.
Hydrogen Peroxide (anhydrous)	Chromium, copper, iron, most metals or their salts, aniline, any flammable liquids, combustible materials, nitromethane, and all other organic material.
Hydrogen Sulfide	Fuming nitric acid, oxidizing gases.
Iodine	Acetylene, ammonia (aqueous or anhydrous), hydrogen.
Mercury	Acetylene, alkali metals, ammonia, fulminic acid, nitric acid with ethanol, hydrogen, oxalic acid.
Nitrates	Combustible materials, esters, phosphorous, sodium acetate, stannous chloride, water, zinc powder.
Nitric acid (concentrated)	Acetic acid, acetone, alcohol, aniline, chromic acid, flammable gases and liquids, hydrocyanic acid, hydrogen sulfide and nitratable substances.
Nitrites	Potassium or sodium cyanide.
Nitroparaffins	Inorganic bases, amines.
Oxalic acid	Silver, mercury, and their salts.
Oxygen (liquid or enriched air)	Flammable gases, liquids, or solids such as acetone, acetylene, grease, hydrogen, oils, phosphorous.
Perchloric Acid	Acetic anhydride, alcohols, bismuth and its alloys, paper, wood, grease, oils or any organic materials and reducing agents.
Peroxides (organic)	Acid (inorganic or organic). Also avoid friction and store cold.
Phosphorus (white)	Air, oxygen.
Phosphorus pentoxide	Alcohols, strong bases, water.
Potassium	Air (moisture and/or oxygen) or water, carbon tetrachloride, carbon dioxide.
Potassium Chlorate	Sulfuric and other acids.
Potassium Perchlorate	Acids.
Potassium Permanganate	Benzaldehyde, ethylene glycol, glycerol, sulfuric acid.
Silver and silver salts	Acetylene, oxalic acid, tartaric acid, fulminic acid, ammonium compounds.
Sodium	See Alkali Metals
Sodium Chlorate	Acids, ammonium salts, oxidizable materials and sulfur.
Sodium Nitrite	Ammonia compounds, ammonium nitrate, or other ammonium salts.
Sodium Peroxide	Any oxidizable substances, such as ethanol, methanol, glacial acetic acid, acetic anhydride, benzaldehyde, carbon disulfide, glycerol, ethylene glycol, ethyl acetate, methyl acetate, furfural, etc.
Sulfides	Acids.
Sulfur	Any oxidizing materials.
Sulfuric Acid	Chlorates, perchlorates, permanganates, compounds with light metals such as sodium, lithium, and potassium.
Water	Acetyl chloride, alkaline and alkaline earth metals, their hydrides and oxides, barium peroxide, carbides, chromic acid, phosphorous oxychloride, phosphorous pentachloride, phosphorous pentoxide, sulfuric acid, sulfur trioxide.

Flammable Liquids

Flammable liquids require special storage considerations. See Flammable Materials for more information.

Acids

Mineral acids, including phosphoric, hydrochloric, nitric, sulfuric, and perchloric acid can be stored in a cabinet designed for Corrosive Acids.  These non-metallic cabinets have no internal metallic parts, acid resistant coating and a cabinet floor constructed to be able to contain spillage. Volatile acids, such as nitric or sulfuric acid, should be stored either in an acid cabinet or in a vented cabinet, such as the fume hood base, particularly after they have been opened.  Concentrated mineral acids can be very reactive, even with each other. Concentrated acids can even react vigorously with dilute solutions of the same acid, if mixed together rapidly. For example: concentrated sulfuric acid mixed quickly with 1 molar sulfuric acid will generate a lot of heat. Different concentrated acids should be stored apart. If stored within the same cabinet, plastic trays, tubs or buckets work well to keep different acids apart within the cabinet.

Acetic acid is an organic acid and should be stored separately from mineral acids.  Since it is also flammable, it is best stored with other flammable liquids.

Picric Acid can form explosive salts with many metals, or by itself when dry. Perchloric Acid is an extremely powerful oxidizer and must be kept away from all organic materials, including wood.   See Section 7d, Corrosives for more information. 

Unstable Chemicals

Ethers and some ketones and olefins may form peroxides when exposed to air or light. Since they may have been packaged in an air atmosphere, peroxides can form even if the container has not been opened.

Some chemicals, such as dinitroglycerine and germane, are shock-sensitive, meaning that they can rapidly decompose or explode when struck, vibrated or otherwise agitated. These compounds become more shock-sensitive with age.

For any potentially unstable chemical:

• On the label, write the date the container was received and the date it was opened.
• Discard containers within 6 months of opening them.
• Discard unopened containers after one year, unless an inhibitor was added.

More information about unstable chemicals is available in Peroxide Forming Compounds and Reactives.

Designated Areas

Any area where particularly hazardous substances, including carcinogens, acutely toxic chemicals and reproductive toxins, are stored or used must be posted as a Designated Area. These materials should be stored separately from other chemicals, as space permits. See Particularly Hazardous Substances for more information.

Compressed Gases

Compressed gases pose a chemical hazard due to the gases themselves and a high energy source hazard due to the great amount of pressure in the cylinder. Large cylinders may weight 130 pounds or more and can pose a crush hazard to hands and feet.

• All cylinders must be secured to a wall, bench or other support structure using a chain or strap. Alternatively, a cylinder stand may be used.
• Segregate cylinders by gas type (e.g., flammable, inert, etc.).
• Store cylinders away from heat sources and extreme weather conditions.

See Compressed Gas Cylinders for more information.

Combustible Materials

Common combustible materials, such as paper, wood, corrugated cardboard cartons and plastic labware, if allowed to accumulate, can create a significant fire hazard in the laboratory. Combustible materials not stored in metal cabinets should be kept to a minimum. Store large quantities of such supplies in a separate room, if possible.

Personal Behavior (top)

Professional standards of personal behavior are required in any laboratory:

• Avoid distracting or startling other workers
• Do not allow practical jokes or horseplay
• Use laboratory equipment only for its designated purpose
• Do not allow visitors, including children and pets, in laboratories where hazardous substances are stored or are in use or hazardous activities are in progress.
• Do not prepare, store (even temporarily), or consume food or beverages in any chemical laboratory
• Do not smoke in any chemical laboratory. Additionally, be aware that tobacco products in opened packages can absorb chemical vapors.
• Do not apply cosmetics when in the laboratory
• Never wear or bring lab coats or jackets into areas where food is consumed.
• Confine long hair and loose clothing in the laboratory. Wear shoes at all times. Open-toed shoes or sandals are not appropriate.
• Under no circumstances should mouth suction be used to pipette chemicals or to start a siphon. Use a pipette bulb or a mechanical pipetting device to provide a vacuum.
• Wash well before leaving the laboratory. Do not use solvents for washing skin.
• Keep work areas clean and free from obstruction. Clean up spills immediately.
• Do not block access to exits, emergency equipment, controls, electrical panels etc.
• Avoid working alone.

Transporting Chemicals (top)

Spills and chemical exposure can occur if chemicals are transported incorrectly, even when moving chemicals from one part of the laboratory to another. One example of such an incident is described in Anecdotes. To avoid this type of incident, consider the following:

• Use a bottle carrier, cart or other secondary container when transporting chemicals in breakable containers (especially 250 ml or more) through hallways or between buildings. Secondary containers are made of rubber, metal or plastic, with carrying handle(s), and are large enough to hold the entire contents of the chemical containers in the event of breakage. A variety of such containers are available from the Chemistry stockroom or from laboratory supply catalogs.
• Transport of hazardous chemicals in individual containers exceeding four liters between buildings is strongly discouraged.
• When moving in the laboratory, anticipate sudden backing up or changes in direction by others. If you should stumble or fall while carrying glassware or chemicals, try to project them away from yourself and others.
• The individual transporting the chemical should be knowledgeable about the hazards of the chemical and should know how to handle a spill of the material.
• When transporting compressed gas cylinders, the cylinder should always be strapped in a cylinder cart and the valve protected with a cover cap. Do not attempt to carry or roll cylinders from one area to another.
• Transport chemicals in freight elevators rather than passenger elevators, if available.
• Keep chemicals in their original packing when transporting, if possible.

Working with Scaled-Up Reactions (top)

Scale-up of reactions from those producing a few milligrams or grams to those producing more than 100g of a product may represent several orders of magnitude of added risk. The attitudes, procedures and controls applicable to large-scale laboratory reactions are fundamentally the same as those for smaller-scale procedures. However, differences in heat transfer, stirring effects, times for dissolution, and effects of concentration and the fact that substantial amounts of materials are being used introduce the need for special vigilance for scaled-up work. Careful planning and consultation with experienced workers to prepare for any eventuality are essential for large-scale laboratory work. See Anecdotes.

Although it is not always possible to predict whether a scaled-up reaction has increased risk, hazards should be evaluated if the following conditions exist:

• The starting material and/or intermediates contain functional groups that have a history of being explosive (e.g., N—N, N—O, N—halogen, O—O, and O—halogen bonds) or that could explode to give a large increase in pressure.
• A reactant or product is unstable near the reaction or work-up temperature. A preliminary test consists of heating a small sample in a melting point tube.
• A reaction is delayed; that is, an induction period is required.
• Gaseous by-products are formed.
• A reaction is exothermic. Consider what can be done to provide cooling if the reaction begins to run away.
• A reaction requires a long reflux period. Consider what could happen if solvent is lost owing to poor condenser cooling.
• A reaction requires temperatures below 0^oC. Consider what could happen if the reaction warms to room temperature.

In addition, thermal phenomena that produce significant effects on a larger scale may not have been detected in smaller-scale reactions and therefore could be less obvious than toxic and/or environmental hazards. Thermal analytical techniques should be used to determine whether any process modifications are necessary.

Unattended Experiments (top)

Laboratory operations involving hazardous substances are sometimes carried out continuously or overnight with no one present. It is the responsibility of the worker to design these experiments so as to prevent the release of hazardous substances in the event of interruptions in utility services such as electricity, cooling water, and inert gas.

• Laboratory lights should be left on, and signs should be posted identifying the nature of the experiment and the hazardous substances in use.
• If appropriate, arrangements should be made for other workers to periodically inspect the operation.
• The Emergency Information Poster should include contact information for the responsible individual in the event of an emergency.
• Carefully examine how chemicals and apparatus are stored, considering the possibility for fire, explosion or unintended reactions. A description of a fire that occurred in a fume hood when an experiment was left unattended for several days may be found in Anecdotes.

Working Alone (top)

• If working alone is absolutely necessary, the worker should have a phone immediately available and should be in contact with another person (who knows that he or she is being relied upon) at least every 30 minutes.
• If no one from the laboratory is available, contact Public Safety at 258-3134 and request that the dispatcher check back by phone at regular intervals.

The laboratory supervisor or PI is responsible for determining whether the work requires special precautions, such as having two people in the same room for particular operations.

Section 7B: Flammable Materials

Section 6C: Personal Protective Equipment