1
CHE 450G SAFETY EXAMINATION
Procedure:
Before lab keys are issued to a new student, he or she must pass the Inorganic Department Safety Examination. A copy of the exam with answers is given to the new student by the group safety officer to study. When the student is ready to take the examination, the copy with the answers is returned and the student is supplied with a copy of the exam without answers. The test is administered by the safety officer in a location of his or her choice. The test is to be taken in private without outside resources. No time limit is imposed.
The exam is to be graded by your TAs prior to beginning scheduled laboratory experiments. If incorrect or incomplete answers are given, the TA and/or instructor will review these areas with the student. The graded and reviewed exam is then passed on to the instructor. The TAs will then return a copy of the exam with answers to the student for future reference.
Safety Exam Questions
PartI. General Lab Safety
1.What safety references should you consult to assess the hazards of a chemical or planned experiment?
The chemistry library has several texts on safety in the reference section:
Prudent Practices in the Laboratoryon-line summary
Safety in Working with Chemicals
Sigma-Aldrich Library of Chemical Safety Data
Merck Index
Aldrich Catalog
On-line MSDS sheets:
Univ. of Ill. MSDStelnet://romulus.ehs.uiuc.edu:3000
Fischer Scientific MSDS
Safety TechLine 1 800 356-2501
2.What steps should be taken when injured in lab?
Get TA and instructor
Stop bleeding if necessary
Wash affected area with cold water (if chemicals are unreactive with water)
Seek medical attention as necessary
3.Compressed gas cylinders are quite common in inorganic labs. Discuss their handling, use, and transport.
Even if a gas cylinder contains an inert gas, it should be handled carefullybecause of the high pressures involved. Tanks should always be strapped or chained to a stable surface and should only be moved on a cart designed to transport them. A metal valve cover cap should enclose the valve before moving
as well. Each type of gas requires a particular regulator. Oxygen tanks in particular require regulators free from hydrocarbon grease. Teflon tape should never be used.
4.General vocabulary as seen on the Safety Examination (answered verbally to the group safety officer):
DewarAspirators
Vacuum pumpSchlenk line
Alkali metalRotary evaporator
MercaptanHeating mantles (Variacs)
Base bath/Acid bathPhosphine
Bleach
5.How should you dispose of the following reactive wastes? (each should be done in a well-functioning ventilation hood while stirring the mixtures) For more detailed descriptions see Prudent Practices for Disposal of Chemicals from Laboratories and/or
a.Oxidizing agents (chromates, permanganates, chlorates, etc.)
Acidify a dilute solution (<5%) to a pH<3 with sulfuric acid and slowly add a 50% excess of aqueous sodium bisulfite.
b.Sodium borohydride
Add water slowly until the solution is less than 3%. Add excess aqueous acetic acid dropwise with stirring under nitrogen.
c.Mercaptans and sulfides
Add a 25% excess of bleach to oxidize these compounds with stirring; sometimes a more concentrated bleach substitute, calcium hypochlorite (swimming pool chlorine, HTH brand name) can be used. For a more detailed procedure see Prudent Practices for Disposal of Chemicals from Laboratories page 65.
d.Alkali metals (a major source of laboratory fires)
Add 3:1 kerosene:isopropanol or tert-butanol slowly while stirring. After gas evolution ceases, often several hours or days later, add 95% ethanol slowly with stirring. After the metal has been consumed, and no large solids are evident, add cold water slowly while stirring. Slowly add a 5% aqueous HCl solution until aqueous layer is neutralized (pH ~ 7). Place organic layer into the non-halogenated waste jerry can and pour the aqueous mixture down the sink so long as no solids are visible.
e.Metal sulfides
Add slowly to ice water. Keep in hood-H2S evolution.
f.Nonmetal halides
Hydrolyze these compounds by slowly adding them to a stirred 2.5 M solution of sodium hydroxide.
g.Metal carbonyls
Oxidize these compounds with bleach.
h.Nonmetal alkyls (BR3, PR3, AsR3, etc.)
To a dilute (<5%) solution (of the alkylating agent in an inert solvent), slowly add a 10% excess of tert-butyl alcohol in a high-boiling hydrocarbon solvent such as heptane under nitrogen. Add cold water and then 5% hydrochloric acid.
i.Organomercury compounds
Oxidize these compounds with bleach.
Part III.Fires and explosions: Prevention and extinguishing.
1.There are four general classes of fires which are likely to pose a genuine threat to your laboratory safety. What are the four classes of fires and what type of extinguisher is required to put out each fire?Additional information is given below for your benefit, but you need only answer the highlighted question above.
Class A fires:
Ordinary combustible solids: paper, rubber, textiles.
Frequently accompanied by destructive distillation producing flaming vapors or toxic gases. Also may leave hot ash or residue which may initiate ignition. Effectively extinguished by water, which is recommended if the water poses no further hazard. Also extinguished by CO2, N2, volatile halocarbons (CF3Br, etc.), and dry chemical extinguishers, though these may spread ashes due to rapid release of compressed gas from the extinguisher cylinder. Dry ice will usually rapidly smother these fires if it isreadily at hand.
Class B Fires:
Involves flammable liquids.
Spreading of the fire is a major complication which is commonly encountered if a vessel of flaming liquid is overturned or broken. Easily extinguished by the exclusion of air by covering it in an upright vessel or by blanketing in foam, CO2, N2, volatile halocarbons, or sometimes dry chemical (depending on the situation). Again, dry ice or liquid nitrogen is very effective if it is at hand. Compressed gas extinguishers can lead to spreading and worsening of the fire if the force from the extinguisher overturns a vessel containing the flammable liquid.
Class C Fires:
These are Type A or B fires in which electrical equipment is involved.
Can be treated as class A or B, if the power is turned off. Never use water as an extinguisher, even in the event power is disabled (some electrical equipment will store charge, resulting in an electrocution hazard). A CO2 extinguisher is the best extinguisher to use as it does not leave a damaging residue like dry chemical extinguishers. Again, dry ice or liquid nitrogen is very effective if available.
Class D Fires:
These fires involve active metals (e.g. Li, Na, K, Zn, Al, Mg, etc.) or active hydrides (NaH, KH, LiAlH4, etc.).
These fires cannot be extinguished by CO2, HCO3-, H2O, or volatile halocarbons. Inert powder must be used (sand, talc, or alkali metal salts). Bicarbonate extinguishers (dry), Halon, and CO2 extinguishers should not be used as they may react violently with these active species. Metal-X extinguishers are highly recommended.
2.After use of a fire extinguisher, who should be contacted?
Inform your TAs. Call the fire department to get the extinguisher refilled.
3.What should you do if you suspect that an ether is contaminated with peroxides?
Call Environmental Health and Safety to have the bottle in question removed.
4.What precautions must be taken when flame-sealing frozen liquid in an ampule or NMR tube?
Evacuate the NMR tube at room temperature so the inert gas does not condense in the sample when you freeze it. It could cause an explosion when it warms up. Tubes should be warmed slowly in a hood or behind a shield.
5.Name three common methods of heating reaction mixtures and their advantages and/or disadvantages.
(a)Thermostated hot plate
These units create a spark each time they turn on or off which can ignite organic vapors. An external thermostated bath controlled via a thermocouple is safer because the power source is placed away from the reaction mixture.
(b)Heating mantle
These should always be used with a variac controller. A possible problem with heating mantles is that localized hot spots can develop. For this reason, it is recommended that heating mantles be used only for very high boiling solvents or for large reaction flasks that require overhead stirrers.
(c)Stirred oil bath
Oil baths provide provide the best uniform heating. Mineral oil baths are useful for low boiling solvents and should never be heated above 150 ˚C. Silicone oil baths should be used for higher temperatures (up to 250 0C). There is a greater fire hazard with mineral oil baths--stop heating if they smoke.
6.Liquid nitrogen cooled traps (on a vacuum or Schlenk line) should not be left opened to the atmosphere, why?
Liquid oxygen can condense (blue in color) in the trap and explosively react with any oxidizable materials present. Sudden warming or bumping of the oxygen-filled trap which will pressurize the system and may cause an explosion as well.If liquid oxygen is observed in a trap, immediately raise the Dewar (to keep the O2cooled), close any stopcocks to air, and pump out the trap for several minutes.
7.Hazards from explosion or implosion are often present in a chemical laboratory. Potential sources of implosion are rotary evaporators and other evacuated flasks. Respond to each statement and give reasons to support your claim.
(a)The body of a rotary evaporator should not be implosion protected since this would obscure your vision of condensates and the condition of the condenser coil (clean-dirty).
This statement is false since there is a real danger from implosion and
protection can be provided without loss of visibility. Netting of the glass or plastic coating is recommended.
(b)A one-liter flask is the largest which should be evacuated.
This statement is true because of the higher probability of implosion with a larger flask.
(c)The implosion hazard from a water aspirator vacuum (~20 mmHg) is less than that from high vacuum systems (<0.5 mm Hg).
False, both are equally hazardous since it is the differential pressure whichpropels broken glass and both pressures are far from atmospheric pressure.
8.The sinks and benchtops made of a pressed fibrous material which is chemically unreactive to most materials. Explain why dry ice, liquid nitrogen, or cooled baths should not be poured into the sink basins or placed onto the lab counter tops.
While the sinks are chemically inert, they are subject to mechanical damage due to their glass-like properties. The sink basins and counter tops are made from materials having high thermal coefficient of expansion and can be cracked by pouring extremely hot or cold substances into the sink.
9.What precautions should be taken to protect yourself from implosion of dewars or rotary evaporator traps?
Dewars should be taped with elastic electrical tape, and if possible, netted.Rotary evaporator traps should always be netted.
10.Whenever you work with malodorous compounds, care must be taken to be surethat no odor escapes into the atmosphere (even in the hoods).
Phosphines, sulfides, mercaptans, and isonitriles are some of the more infamous examples of such materials. Special chemical precautions must be taken to avoid releasing these materials (especially sulfur compounds) since these odors may alarm people inside and outside the building (ethyl mercaptan gives natural gas its characteristic odor). The phosphorus and sulfur compounds are easily neutralized by passing the gaseous effluent through NaOCl (bleach - very large volumes) solutions, or even better Ca(OCl)2 solutions.
For example 30 mL of CS2 requires that 6.7 L (25 % excess) of household bleach be used while only 2.2 L of Ca(OCl)2 (65% solution, 550 g) is required. A detailed and effective procedure can be found in Prudent Practices for Disposal of Chemicals from Laboratories, page 65.
Glassware, gloves, and hands may be deodorized with a solution of Diaperene, a tetraalkylammonium salt used to deodorize diaper pails. Isonitriles are absorbed by alcoholic iron(II) solutions. In addition to the chemical precautions, what other precautions should be taken?
UK OHSHA should be notified in advance of mercaptan or other malodorous compound use. The exact location and experiment duration should also be provided to Howard and the fire department.
Part IV.First Aid and Health Hazards
1.In an emergency, there are certain telephone numbers that you should have memorized or have easy access to:
Emergency (police, fire dept., paramedics)9-911
Poison Control Center1-800-543-2022
2.In the event of chemical splashes or spills, it may become necessary to thoroughly flush chemical from contact with your skin. How is this done?
For spills on your hands or arms, you will usually be able to wash the chemicals off over the sink. Remember you should use cool water to rinse as warm water opens skin pores, thus accelerating systemic absorption. The affectedareas should be washed for at least 15 minutes. For large chemical spills orcontamination in or around the eyes, each lab in Chemistry-Physics are equipped with safety showers and eye wash stations.
- In the event that you or one of your group members is cut, there are two preferred methods that are recommended to control blood loss. Describe the two methods.
For serious bleeding apply direct pressure, elevate the wound above the heart, and call for medical assistance. If the cut is minor, control the bleeding through direct pressure and go to a hospital emergency room or to the UK Student Health Center (see question #2 of Part I).
Direct pressure by hand over the dressing is the preferred method for control of bleeding since it limits blood loss without interruption of circulation. This should be used in conjunction with elevation of the affected region.
4.In the event that a strong acid or base is spilled onto your skin or clothing, what is the correct procedure for minimizing chemical burns of the skin?
(a)Remove clothing from the areas involved.
(b)Wash away the chemical with large amounts of water using the sink or safety shower in your lab (whichever is appropriate), as quickly as possible for at least 5 minutes.
(c)Apply a concentrated solution of sodium bicarbonate to neutralize the acid or base after flushing with water.
(d)Apply a dressing bandage and call for medical aid.
5.There are two classifications of thermal burns that we will be concerned with: first- and second-degree burns. First-degree burns result from slight skin contact with hot solids or liquids A red appearance of the skin results. Second-degree burns are those resulting from longer-duration contact with hot liquids, surfaces, or burning materials. Blistering and reddening of the skin are characteristic of second-degree burns. How should you treat each of these cases?
(a)First-degree burns
Apply cool water (not ice water), or immerse the affected area in cool water for several minutes. Dry by blotting and apply dressing (gauze) if necessary.
(b)Second-degree burns
Immerse the affected area in cool water (not ice water) until the pain subsides.
Blot dry, gently.Do not break blisters or remove tissue.
Apply dry, sterile gauze or clean cloth as a protective bandage.
Do not use an antiseptic preparation, ointment, or spray on a severe burn.
If the arms and legs are affected, keep them elevated.
Seek medical assistance.
6.What are the problems associated with wearing contact lenses in a chemical laboratory?
Chemicals or other materials entering the eye can be physically held against the eyeball and not washed free due to contact coverage. Soft contacts will often absorb organic vapors like MeOH, CHCl3, or other serious lachrymators. If you should become unconscious after a laboratory accident, the attending medical personnel will most likely be unaware that you wear contacts. Quite often contacts will displace to one corner of the eye, making easy identification of contact users difficult if not impossible. Serious eye damage could result. Contacts should never be worn in the lab and should be replaced bycorrective glasses made of impact resistant material (polycarbonates).
7.Food storage and consumption in a chemical area is a health hazard. Outline the problem and preventive measures to avoid accidental chemical poisoning.
Food and drink are never allowed in a chemical area since they can become contaminated with dangerous chemicals by direct contact with airborne dust, surfaces, and vapors. Areas where food is to be consumed or stored must be clearly labeled as a non-chemical area, and laboratory reagents and chemicals must be clear of this space. Eating in the laboratory is not recommended.
8.The clothing you wear in the laboratory is a factor which will influence your safety.Outline appropriate and inappropriate clothing, and indicate hazards associated with wearing each in a chemical laboratory.
Loose clothing should not be worn since it may be accidentally exposed to
chemical contact or become caught in machinery. It also presents a greater fire hazard. Long hair can also be a problem because it can easily catch fire or become entangled in equipment. "Skimpy" clothing will offer little protection in the event of a chemical splash or spill. Shoes must be worn at all times. Perforated shoes or sandals should not be worn in the lab. Hosiery should not be worn since it will react or dissolve ("melt") upon contact with acid and some chemicals. The "melted" hosiery and chemicals trapped in it will adhere to the skin and are likely to increase the severity of a chemical burns.