CHEMICAL LABORATORY SAFETY SAFE LABORATORY PROCEDURES

Objectives

This section describes the procedures which are commonly used in the laboratory and which are the most common sources of accidents or are the least understood.

GLASSWARE

Lacerations from broken glassware are common laboratory injuries but most could be avoided by following safe procedures for handling and working with glassware.

Stress and Flaws

Glassware breaks due to stress.

Stress that is insufficient to cause breakage of the glassware may cause flaws which will later contribute to breakage.

A flaw can be created by a thermal or bump check.

• Thermal Check - uneven heating or sudden changes in temperature.
• Bump Check - striking with a hard surface or scratching.

Flawed glass can break when subjected to stress from increased vacuum or pressure, being dropped, or through uneven heating.

Inspect glassware for chips and cracks before use (polarscopes are useful for this).

If defects in the glass are observed, DO NOT use the glassware.

Chipped and cracked glassware is nothing more than an accident looking to happen.

PROTECT YOURSELF

Protect your hands from broken glass. Use leather gloves to pick up broken glass.

Use gloves when unscrewing a stubborn cap on a glass bottle.

NEVER try to catch falling glass.

INSERTING GLASS TUBING

The most common cause of lacerations is glass tubing which breaks while being pushed through a rubber stopper.

Lubricate with glycerin, hold by the base of the tube, and use leather gloves.

USING PRESSURE or VACUUM

All glassware which is being subjected to increased pressure or reduced vacuum should be taped with fiber-reinforced tape.

The setup should also be placed behind a shield.

CHEMICAL TRANSFERS

Improper transfers of chemicals are another frequent cause of accidents.

When pipeting, always use a mechanical device to create suction in the pipet.   Never use your mouth.

Pouring is a common method of transfer.    There are several rules to observe when pouring:

• pour from large bottles to immediate sized beakers to the final destination.
• use a stirring rod to control pouring.
• pour away from the label to protect the label from the chemical and wipe the cap threads when finished.
• use a pump on five gallon bottles.

When transferring flammable liquids, make sure any metal containers are grounded.

When carrying a glass container of chemicals, use a bottle carrier to cushion it and protect against spills. (remember chemical incompatibility)

When opening ampules, cool the contents with ice or dry ice before opening.

Never reseal flammable liquids contained in a ampule.    Transfer the flammable to a storage bottle and use paraffin as a seal.

When adding chemicals to a reaction, be aware of the order in which the chemicals are added.

Acids are always added to water.

CRYOGENS

Cryogens are materials used maintaining extremely low temperatures.   These substances are hazardous for several reasons.

• Cryogens can injure living tissue as badly as a high temperature source.
• Cryogens can cause asphyxiation upon evaporating.
• The liquid state gives them a higher concentration that exaggerates the hazardous properties.

Whenever handling or transferring cryogens, wear loose fitting heavily insulated gloves.   Keep in mind that the higher the heat capacity of the substance, the greater the danger of burns.

Liquefied gases have extremely high expansion ratios.    Nitrogen expands by a factor of 700 in going from a liquid to a gas.    A 60 liter dewar of liquid nitrogen, if released, can displace enough air in a 400 cubic meter room to cause asphyxiation.

Cryogens are stored in large highly insulated containers.   These containers have vents to allow the continuous escape of gas to prevent a buildup of pressure.   mproperly handling the container can allow air inside and moisture can freeze and plug the vent.

Liquefied gases are very concentrated which can exaggerate their hazardous properties.  Liquid oxygen can cause organic materials to spontaneously burst into flames.

Be aware that oxygen can condense from the air into your liquefied system whenever you have temperatures below the condensation point of oxygen (-183 C).   For example, oxygen can condense on the finger of a cold trap and react with organic residue.

HEATING METHODS

Always choose the best heating method for your purpose.

• If heating to less than 100 ^oC, use a water bath.
• If heating to slightly greater than 100 ^oC, use steam.

For higher temperatures, there are several options:

• hot plate/stirrer

• heating mantle

• oil bath

• sand baths

• heat guns and Bunsen burners

Hot plate / stirrer

Be aware that the thermostat can form an electric arc which is a dangerous ignition source when heating flammable liquids.

Use an explosion-proof hot plate.

Electric Heating Mantle

A less hazardous source of heat than the hot plate but suffers from problems with hot spots.   Heating mantles which fit most shapes and sizes of glassware are commercially available.

Oil Baths

A more uniform source of heat than the heating mantle is the oil bath.   Silicone oils are available to provide different viscosities and useful temperature ranges.

Be aware that these oils decompose at around 300 ^oC and decomposition results in toxic products temperature control is lost.

Although oil baths give uniform heating, they do not cool rapidly.   A jack is recommended to adjust the heat.

Be careful not to contaminate the oil.

Contamination can drastically reduce the flash point of the oil.   Load reactants into the vessel before placing it in the bath.    Make sure that the reaction vessel doesn't overflow into the oil bath.

Over-temperature controls are recommended for use with oil baths.   Instead of just one thermostat, a second is set to turn off the heating element if the temperature of the oil rises 5 to 10 degrees above the desired temperature.   This mainly acts as a backup for the primary controller.

Heating to Higher Temperatures

Still higher temperatures require other more hazardous heat sources such as molten salt baths, Wood's metal, and fluidized sand baths.

• salt baths - sometimes strong oxidizers

• Wood's - toxic fumes

• Sand baths - fine dust

Heat Guns and Burners

Heat guns and burners should never be used near flammable liquids.   Flammable vapours are drawn into the heat gun and contact the electric heating coils.

COMPRESSED GASES

Every employer should have a comprehensive policy regarding compressed and liquefied gases in cylinders.   Gas cylinders are hazardous because of the high pressures within them.

There are a few basic rules you should know about handling compressed gas cylinders.

• When moving a cylinder, always use the shipping cap.

• Always secure it from falling.

Cylinders containing gases which are neither poisonous or flammable are equipped with safety relief devices to release pressure if the pressure inside gets too high.   Make sure the ports are not plugged or corroded.

If the gas you are using is corrosive, never leave valves and regulators under pressure for long periods of time and always relieve the pressure in the system after use.   Corrosives under pressure will corrode the valves and make it impossible to turn off later.

Never empty a cylinder completely.   Return the cylinder to the vendor with about 25 psi remaining.   This will prevent the cylinder becoming internally contaminated and causing problems later.

Use a regulator designed for the specific gas you are using.   Some gas cylinders have right handed connection while others have left.    This is to insure that gases and regulators which are incompatible are not used together.   NEVER use an adapter to defeat the safety feature.

Don't use lubricants with gases which are oxidizers.   The oxidation of grease is highly accelerated in the presence of a pure oxidizing gas under pressure and can cause an explosion.   Parts which come into contact with an oxidizing gas should also be decreased.

Gas cylinders are labeled according to Department of Transportation (DOT) requirements.  Gases are labeled as one or more of the following:

• nonflammable flammable

• corrosive poisonous

• oxidizer radioactive

Two very common laboratory gases are hydrogen and acetylene.   Both gases are flammable.

Acetylene is supplied in 250 psi cylinders but this is possible only because the acetylene is dissolved in acetone packed in a porous material.

Outside of this medium, acetylene will explode violently above 15 psi and the higher the pressure, the less shock is required to cause an explosion.

Acetylene can also react with copper to form explosive acetylides.   NEVER use copper tubing with acetylene.

Hydrogen can be ignited by a small amount of energy.   A hydrogen leak will usually ignite spontaneously because static electricity is formed by the gas movement or dust particles.

All flammable or toxic gases should be used in a fume hood.   If the bottles are too large, consult your employer's rules.

Compressed gas cabinets are available that provide ventilation, fire resistance, and a metal door for changing and adjusting cylinders.

One of the best engineering controls for hazardous gases is the critical orifice.   This is a tiny hold that limits the maximum volume of gas per unit time that can flow through the hole for a specific pressure drop.

Critical orifices have two shortcomings:

• they can be plugged from dirt outside the cylinder

• they don't provide a positive shutoff in emergencies

The dirt problem can be solved by including a filter ahead of the orifice.

The positive shutoff can be provided by an excess flow valve which snaps shut when the pressure drops exceeds a preset limit.

Other engineering solutions are:

• purging hardware

• detectors for toxic or flammable gases

• overpressure relief valves

WASTE DISPOSAL

Chemical waste disposal is a complex subject because local and state codes determine permissible disposal practices.   These codes are generally based on federal regulations (EPA) and thus a common foundation.

Local conditions and the local administration of sewerage treatment plants force different rules in different areas.   Follow your employer's rules on this subject.

Waste disposal begins with minimizing waste.

• Use the smallest amount of chemical possible.

• Make use of surplus chemicals first.

• Convert your waste to less hazardous or nonhazardous chemicals if possible.

• Use scrubbers to trap or neutralize gaseous waste.

EMERGENCY EQUIPMENT and PROCEDURES

Mistakes happen.

When they do, you must be prepared to deal with the consequences.   One key to dealing with these emergencies is understanding what should be done and have the training to do it.

Eyewash Fountains and Showers

ANSI Z358.1 gives performance and design specifications.    When placing these, the specification maintains a maximum of 100 feet or 10 second travel time.   Eyewashes should be located within the laboratory room.

Test the showers and eyewashes periodically to ensure performance and clean out any rusty water.

Know instinctively where the eyewash fountain is.

Hold your eyelids open with your fingers and roll your eyes around to clean all areas.   Flush 15 minutes.

Portable eyewashes should not be used unless they provide 15 minutes of water.   Change the water frequently since it is subject to the growth of harmful bacteria.

The portable eyewash should do both eyes.

If you need to use an emergency shower, walk quickly to the nearest one.   Remove all clothing as you can since clothing keeps the chemical in contact with your skin.   Leave goggles on until you are sure all chemicals have been washed from your hair and scalp.

Fire extinguishers

OSHA provides several approaches to dealing with a fire.

• flee

• fight

• provide local extinguishers

Flee - evacuate the building a call professionals

Fight - form a trained and equipped fire brigade comprising of about 10% of the lab population.  In this case, extinguishers are for only those trained in their proper use.

Provide extinguishers - provide fire extinguishers in all the laboratories and train laboratory personnel in their use.   This training is designed to teach personnel to use hand-held extinguishers, but not to fight significant fires.

Fire extinguishers should be placed by the door of the laboratory.   This allows you to position yourself between the fire and the exit.

Spill Cleanup Kits

Spill cleanup kits are specific for many different types of chemical spills.   A kit usually includes gloves, an absorbing or neutralizing medium, a pan, and a bag.   Be sure you know how to use the kit and dispose of the material after cleanup.

Know How to Handle an Emergency Situation

• Your employer should provide you with a written document describing all emergency procedures.

• Read it carefully. It provides you with the best professional help in the shortest period of time while complying with all pertinent laws and regulations.

• Make sure all emergency equipment is accessible.

• Emergency procedures should be explained to you on the first day of work

• Know what to do in case of a medical emergency, fire emergency, or chemical spill.

• Know how to turn in an emergency call and how to respond to an emergency.

• There should be an evacuation plan and map posted in your area.

• Be aware of the work being done around you, especially if it is hazardous.

• Know what to do in case a laboratory worker becomes frozen due to high-voltage.

• Do you know where the circuit breakers or power switches are located?

• Do you know the first aid procedures associated with the chemicals you are working with?

• Be prepared to help others.

SPECIAL PROCEDURES

There are special procedures which should be followed when working with chemicals of the following properties: (Prudent Practices for Handling Hazardous Chemicals in Laboratories)

MODERATE CHRONIC or HIGH ACUTE TOXICITY

When working with chemicals of moderate chronic or high toxicity, a second person should always be present.

The second person should know the emergency procedures and first aid associated with the chemical.

Work with moderately chronic or highly acute toxins only in designated areas.

In addition to other protective equipment, protect you hands and forearms by wearing either gloves and a lab coat or long gloves to avoid contact of toxic material with the skin.

Procedures involving volatile or gaseous toxic substances or possible generation of toxic aerosols should be conducted in a fume hood or other suitable containment device.

After working with toxic materials, wash your hands and arms immediately.

Never eat, drink, smoke, chew gum, apply cosmetics, take medicine, or store food in areas where toxic materials are being used.

Place apparatus containing these materials in or above catch-pans made of impervious plastic or line the surfaces of hoods with plastic-backed paper.

Place warning signs in the area and use a scrubber or condense vapours before releasing to the hood exhaust.

HIGH CHRONIC TOXICITY

When dealing with chemicals which exhibit high chronic toxicity, follow the rules for highly acute toxins plus the following additional procedures:

Plan the experiment from beginning to end, including decontamination and waste disposal.

Review your plans with others to make sure you have not overlooked anything.

Record amounts stored and amounts used.   Also record dates of use and users.

Store and use chemicals in a controlled access area.    Store the chemicals in a secondary container in case of breakage.

If a glove box is used, the ventilation rate should be at least 2 air changes per hour and the pressure within the box should be at least 0.5 inches of water negative with respect to the room.   Exhaust gases should be treated with a scrubber or HEPA filters.

Besides gloves, additional personal protective equipment may be necessary depending on specific material and procedures.   Consult your supervisor.

Upon leaving, wash and dispose of protective clothing according to local rules.

Chemical disposal must follow local rules.    The best procedure is chemical detoxification.

If the chemicals cannot be detoxified, they must be well packaged and labeled as a suspected carcinogen or a chemical of high chronic toxicity.

HIGH FLAMMABLES

Chemical which exhibit high flammability should be kept away from points of ignition.

Never heat over an open flame or with a hot gun or hot plate. Use water, steam or an oil bath if possible.

Electrically ground any metallic containers to prevent sparks caused by static electricity.

Work in a fume hood if possible to keep vapour concentrations as low as possible.

Follow all local fire codes when dealing with flammables, and remember the OSHA regulations regarding containers and quantities.

HIGH REACTIVITY

When dealing with chemicals which are classified as highly reactive, review your plans with others to make sure you have not overlooked anything.

Limit the quantity of chemical to a minimum necessary to do the experiment.

Wear safety goggles, lab coat and a full face shield with throat and ear protection when you are exposed to the chemical. Heavy gloves are necessary and either handle the reaction vessel remotely or with tongs.

Use shields as primary barricades.