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Dr Mike Casey

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Safety is of paramount importance in the laboratory. ... Thiols, volatile sulfides & disulfides often have a terrible tench and some are toxic. ... – PowerPoint PPT presentation

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Title: Dr Mike Casey


1
Safe Handling of Hazardous Chemicals
  • Dr Mike Casey
  • UCD School of Chemistry Chemical Biology
  • Safety Training Course, September 2007
  • Basic Rules
  • Hazard Assessments
  • Common Classes of Hazardous Chemicals

1
2
  • Safety is of paramount importance in the
    laboratory.
  • You have a moral and legal responsibility to work
    safely.
  • Your supervisor is responsible for ensuring that
    you work safely.

3
  • 1. Basic Rules Avoiding Common Hazards
  • Treat all chemicals with caution.
  • Always wear safety spectacles and a lab coat.
  • Do not get any compounds, especially those for
    which no specific safety information is
    available, on your hands or skin.
  • Do not breathe vapours or dust.
  • Use protective clothing, e.g. gloves, as
    necessary and only handle more dangerous or
    unpleasant compounds in fume cupboards.
  • Wash your hands thoroughly immediately after
    leaving the lab.

3
4
  • Do not leave spillages.
  • Clean up spillages promptly and safely.
  • It is particularly important that you clean up
    spillages in communal work areas, e.g. beside
    balances or instruments.
  • Dispose of hazardous material safely.
  • Proper methods for disposal of waste solvents and
    chemicals must be used. Consult your supervisor
    and books on safe disposal procedures. Do not
    allow hazardous waste or spent reagents to
    accumulate, deal with them promptly.
  • All sharps must be placed in the special bins
    provided.
  • All laboratory waste must be segregated in the
    special bins provided.

4
5
  • What to do if chemicals get on your clothing or
    skin, or in your eyes.
  • If a hazardous chemical gets on your clothing,
    remove the contaminated clothing and wash any
    area of skin that might have been affected with
    copious amounts of water. Continue washing for
    at least 5 minutes.
  • If a hazardous chemical gets on your skin, seek
    help from colleagues or supervisors, and wash
    immediately with copious amounts of water.
    Continue washing for at least 5 minutes.
  • If any chemical gets in your eyes, summon help
    and wash immediately with water. Try to wash
    under the eyelids, and continue washing until
    arrangements are made to take you to hospital for
    an eye check.

5
6
  • Be aware of the danger of fires.
  • The consequences of a fire are potentially
    catastrophic.
  • Many solvents are both volatile and flammable,
    and may ignite if the liquid or the vapour comes
    in contact with flames or hot surfaces.
  • Diethyl ether and hydrocarbons, e.g. petroleum
    spirits, are particularly dangerous in this
    respect.
  • Take great care with solvent stills. Make sure
    that they do not run dry, or overflow. Never
    leave them running unattended.
  • Do not use a Bunsen or any other naked flame
    except in specifically designated areas.
  • If the fire alarm sounds, quickly secure any
    potentially dangerous apparatus or chemicals, and
    leave via the nearest fire exit. Obey all
    instructions from the fire marshals.

6
7
  • What to do if there is a fire.
  • If there is a very small fire, consider if it can
    be extinguished by cutting off the oxygen supply,
    e.g. by placing a clock glass over a vessel
    containing a burning chemical.
  • If the fire is larger, or you are in any doubt,
    summon help and leave the area.
  • If the fire is small and you have been trained in
    the use of fire extinguishers, try to use the
    appropriate extinguisher. Otherwise leave the
    area, and if necessary, set off the fire alarm.
  • If the fire alarm sounds, leave the building
    immediately via the nearest emergency exit. Obey
    all instructions from fire marshals.

7
8
  • Do not work alone.
  • It is a strict rule that you never do
    experimental work unless there is another person
    close by.
  • If you are working out of hours, you must sign
    the register beside the main entrance.
  • Obey the rules regarding unattended experiments.
  • Unattended experiments are potentially very
    dangerous, strict adherence to the Departmental
    guidelines is required.
  • Only use thermostatted heating baths.
  • Fit water switches to reflux apparatus, so that
    the power will be cut off if the water pressure
    drops.
  • Secure water tubing to taps and apparatus
    securely using plastic ties.

8
9
2. Hazard Assessments The School Safety
Instructions, and the law, require that you check
the hazards of, and safe handling procedures for,
all chemicals and procedures that you may
encounter before you carry out experimental work.
This requirement is implemented by means of
hazard assessments.
  • There is a strict requirement that you carry out
    a "hazard assessment" before starting each new
    experiment.
  • The safety audit consists of
  • A thorough assessment of the potential hazards
    arising from the use of chemicals and apparatus.
    Consult "Material Safety Data Sheets" (MSDS) and
    related sources to obtain information on hazards.
  • A listing of the control measures to be adopted
    to minimise the risk of an accident.
  • An assessment of the level of the risk involved.

9
10
  • Information on hazards and safe handling
    procedures
  • The information you will need can be found in
    various books including "The Sigma Aldrich
    Catalogue of Safety Data", "Hazards in the
    Chemical Laboratory", and Prudent Practices in
    the Laboratory (also available online).
  • A collection of International Chemical Safety
    Cards, which are very nicely presented summaries
    of essential safety data for compounds, is
    available at http//www.ilo.org/public/english/pr
    otection/safework/cis/products/icsc/dtasht/index.h
    tm.
  • Extensive compilations of "Material Safety Data
    Sheets" (MSDS) are also available on the UCD
    computer servers and on the internet. A very
    useful site from which you can search for MSDSs
    is http//hazard.com/msds/.

10
11
  • Information on hazards.
  • Brief "Safety and Risk Phrases" can be found for
    each compound in chemical suppliers catalogues.
    For example
  • R12 is Extremely flammable.
  • R23/24 is Toxic by inhalation and in contact
    with skin.
  • S15 is Keep away from heat.
  • S36/39 is Wear suitable protective clothing and
    eye/face protection.
  • MSDSs tend to contain exhaustive listings of
    every possible hazard. It is sometimes difficult
    to pick out the hazards that you really need to
    be concerned about. The ICSCs and risk and
    safety phrases highlight the hazards more
    clearly.
  • Watch out for phrases such as highly or
    extremely flammable, explosive, toxic or very
    toxic, severe, cancer, etc.

11
12
  • 3. Common Classes of Hazardous Substances
  • Solvents Dont become complacent about commonly
    used solvents
  • Several, including hydrocarbons, ethers, alcohol
    and acetone are highly flammable (see earlier).
    These are also incompatible with many oxidising
    agents.
  • Chlorinated solvents may react explosively with
    alkali metals and react violently with alkyl
    metals. Chloroform (CHCl3) is sensitive to base
    and may react violently with acetone in the
    presence of base. Keep waste chlorinated
    solvents separate from non-chlorinated.
  • Some, including benzene, carbontetrachloride,
    hexane and hexamethylphosphoric triamide (HMPA)
    are known carcinogens. Use them only if
    absolutely necessary, and work carefully in good
    fumehood.
  • Acetonitrile (CH3CN) is toxic.
  • Nitromethane, and other nitroalkanes can react
    violently with strong bases and with bromine.
  • Dimethyl sulfoxide (DMSO) reacts very vigorously
    with acid chlorides and other reactive
    electrophiles.

12
13
  • Alkali metals
  • Sodium is still widely used for drying solvents.
    It reacts violently with water with formation of
    the highly flammable hydrogen! Take great care
    in disposing of sodium residues. Quench by slow
    addition of isopropanol, caution H2 evolution,
    and then ethanol, before adding water.
  • Never use sodium to dry chlorinated solvents a
    violent explosion may result.
  • Potassium is much more reactive than sodium and
    requires extreme care.
  • Metal hydrides
  • Sodium hydride (NaH) and potassium hydride (KH)
    are finely divided powders which are used as
    powerful bases. They react violently with water
    with formation of the highly flammable hydrogen
    gas, and ignite on contact with moist air. They
    are stored as suspension in mineral oil, which
    are relatively safe and can be exposed, briefly,
    to the air.
  • Sodium and potassium amides (Na/KNH2) have
    similar reactivity.
  • Lithium aluminium hydride reacts violently with
    water. Be careful in working up reactions. Use
    pellets rather than powder, if possible, because
    the powder can be blown around, dispersed by
    static, etc. Keep away from filter paper, other
    combustible materials.
  • Diisobutylaluminium hydride (DIBAL), another
    useful reducing agent, is sold as solutions in
    hydrocarbon solvents. It is extremely reactive
    to air and moisture and must be handled using
    inert atmosphere techniques (see alkyllithiums
    below).

13
14
  • Alkyllithiums and other alkylmetals
  • Available as solutions in hydrocarbon solvents
    and used as powerful bases and nucleophiles.
    React violently with water and air. Must be kept
    under an inert atmosphere and transferred using
    syringe techniques. Consult textbooks and more
    experienced colleagues for instruction on safe
    technique.
  • Old bottles must be disposed of carefully and
    promptly, and not allowed to accumulate. Once
    you suspect that the solution has deteriorated,
    quench by slow addition to isopropanol.
  • Tert-butyllithium is pyrophoric and needs special
    syringe techniques.
  • Grignard reagents, alkylaluminium and alkylzinc
    compounds, and boranes have similar reactivity
    and must be handled using inert-atmosphere
    techniques.
  • Many of these compounds also react violently with
    halogenated solvents.

14
15
  • Halogens
  • Bromine is toxic and highly corrosive and it
    reacts violently with many easily oxidisable
    compounds.
  • Iodine is harmful by inhalation and by contact
    with skin.
  • Chlorine and fluorine are very reactive toxic
    gases that require use of special procedures.
  • Strong Lewis acids
  • Several metal halides and metalloid halides
    (AlCl3 , PCl3, PCl5, BCl3, BBr3, etc) react very
    vigorously with water. Handling details vary,
    but be careful with these strong Lewis acids.
  • Acyl halides and related compounds
  • Acid chlorides react vigorously with water and
    other nucleophiles with the formation of highly
    corrosive HCl. Many have pungent unpleasant
    odours. Keep them in well-sealed containers,
    preferably with an outer container as well.
  • Oxalyl chloride is particularly reactive.
  • Phosgene (ClCOCl) is a very toxic gas and should
    not be used unless absolutely necessary.
  • Many inorganic acid halides (SOCl2, POCl3, etc)
    are similar to organic acid chlorides, as are
    various anhydrides such as phosphorus pentoxide
    (P2O5) and barium oxide (BaO).

15
16
  • Alkylating agents
  • Strong alkylating agents are generally very
    toxic.
  • Iodomethane is very volatile aand toxic. Be
    careful in working up reactions.
  • Dimethyl sulfate (Me2SO4) is toxic, can cause
    severe burns and is aprobable human carcinogen.
  • Methyl triflate (MeOSO2CF3) is a powerful
    alkylating agent and is very toxic.
  • Many benzyl halides (ArCH2X) are potent
    lachrymators. Careful containment, cleaning and
    disposal needed.
  • Sulfur compounds
  • Thiols, volatile sulfides disulfides often have
    a terrible tench and some are toxic. Careful
    containment, scrubbing, cleaning and disposal
    needed. Advance notice must be given to John
    Coffey if they are to be used.
  • Hydrogen sulfide (H2S) may be generated in
    reactions of some sulfur compounds. It is
    volatile, toxic, and extremely foul smelling, and
    requires the same precautions as above.

16
17
  • Oxidising agents
  • Strong oxidising agents, e.g. mCPBA, tBuOOH,
    H2O2, O3, CH3CO3H, KMnO4, and R4NMnO4 are widely
    used . They may react violently with easily
    oxidised materials, such as alcohol, acetone and
    hydrocarbons, to cause fire or even explosion.
    Check carefully for chemical incompatibility
    before use ands keep them away from potential
    fuels.
  • Perchloric acid (HClO4) is also a strong
    oxidising agent and nitric acid (HNO3)
    sufficiently oxidising to ignite ethanol and
    other solvents
  • OsO4 is very toxic.
  • Explosion hazards
  • Hydrogen gas is extremely flammable and forms
    explosive mixtures with air.
  • Azides (RN3) are prone to explosive
    decomposition. Extreme care is needed, and you
    should only work with small quantities, use
    shields, etc. Sodium azide (NaN3) is also toxic.
  • Diazonium salts (ArN2X) are potentially explosive
    and should be kept cold and never be isolated
    from solution.
  • Many perchlorate salts are highly explosive, and
    perchloric acid (HClO4) is very corrosive and
    strongly oxidising.
  • Diazomethane (CH2N2) is prone to explosive
    decomposition. Extreme care is needed, working
    with small quantities only, and special glassware
    must be used.

17
18
  • Miscellaneous very hazardous substances
  • Carbon monoxide Extremely toxic gas and is
    odourless so there is no warning.
  • Cyanide salts, Hydrogen cyanide Extremely
    toxic. Special permission needed for use,
    special precautions must be in place. Consult
    John Coffey before use.
  • Hydrofluoric acid (HF) Causes very severe burns.
    Special permission needed for use, special
    precautions must be in place. Consult John Coffey
    before use.
  • Many compounds of Cr, As, Cd, Pb, Hg, and Be are
    very toxic.
  • Heterogeneous hydrogenation catalysts
  • Hydrogenation catalysts, particularly palladium
    on carbon (Pd/C), and Raney nickel, especially
    when they have hydrogen adsorbed on their surface
    are pyrophoric and will ignite easily combustible
    materials. They should be kept under an inert
    atmosphere and, if possible, kept wet. Dry
    catalyst should never be added to an organic
    solvent in the presence of air, and great care
    should be taken when working up hydrogenation
    reactions.

18
19
  • Conclusion Ignorance is the biggest danger
  • Very hazardous substances can be handled with
    little risk, provided you
  • are aware of the hazards,
  • have found safe purification and handling
    procedures, and
  • have found safe waste disposal procedures.
  • The key is to get advice from your supervisor and
    from senior colleagues, and to consult
    authoritative reference sources.

19
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