Chapter 6: Risk Assessment
A. Section 6.1.1 Living Safely with Hazards
1.
Incident 6.1.1.1 Fatal Lab Exposure
2.
Risk in Labs
a. All activities have risks (driving a car), and labs are no different
b. Assessing Risk in a Systematic Way is a goal of this course
c. We have the knowledge and tools today to minimize (but not eliminate) lab risks
3. Hazard ≠ Risk
a. Hazard = potential source of danger or harm
i. Associated with a chemical or piece of equipment
ii. Does not change; can’t be made to go away
b. Risk = probability of suffering harm from a hazard
i. Can be reduced if the nature of the hazard is understood
ii. Acetone (hazard = flammable); Reduce risk: use in hood, no ignition source
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c. Risk Equation: Risk Level = (Hazard Severity)(Probability of Exposure)
i. Risk of HCN poisoning = (very severe)(small probability if KCN in cabinet)
ii. Risk of acid burn from 0.1 M HCl = (not severe)(high probability used often)
4. Risk Assessment ≠ Risk Management
a. Risk Assessment = identify risks of a new chemical reaction (cryogen involved)
b. Risk Management = steps taken to reduce risk (no sealed vessel, wear gloves)
i. Reducing the amount of the hazard is often a key (smaller scale reaction)
ii. Significant costs can be involved (small yield, much time to repeat)
5. Assessing Probability of Exposure to a Hazard—three main considerations
a. How we use chemicals
i. Contain the chemical—fume hood, closed vessels, good technique
ii. Use Personal Protective Equipment—gloves, lab coat, respirator, etc…
b. How we control the physical environment
i. Knowledge and vigilance against physical hazards required (this course)
ii. Take time to step back and examine the reaction, procedure, equipment
c. Behavior of other people
i. Human error is always preventable
ii. Can’t control others’ actions—assess likelihood of others making a mistake
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6. Risk Assessment Matrix
a. Catastrophic = huge damage to property and/or loss of life [Extreme Risk]
b. Significant/Serious = damage to property and/or serious injury [High Risk]
c. Moderate = some damage and treatable injuries [Moderate Risk]
d. Minor = little damage; injuries treatable by the patient [Low Risk]
e. Categories and risk values: judgment call (you and I might differ)
f. Reconsider your plan if in “Danger” or “Warning” zone: figure out how to fix
7. Perception of Risk
a. Chemists become familiar with chemicals and gain control of procedures
b. This allows us to fairly evaluate risk
c. We can become too familiar and lose perspective on the risk (Ex: distillation)
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8. Example: Prepare 1 L of 1 M H2SO4 from concentrated H2SO4
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B. Section 6.2.1 Globally Harmonized System
1.
Incident 6.2.1.1 Hydrogen Sulfide Leak
2.
GHS = Globally Harmonized System of Classification and Labeling of Chemicals
a. Classification system to help you assess hazards of particular compounds
b. It is complicated, but there are lots of chemicals and hazards in existence
c. More Hazardous = Lower Number
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d. Manufacturers or Suppliers are responsible for classifying based on known data
e. We don’t have to classify; our goal is to use system to assess risk
3. Acute Toxicity Data and Chemical Toxic Hazards
a. Most data comes from animal testing (human poisoning or accidents also)
b. MSDS sheets may have this data, but they are notoriously unreliable
c. LD50 values help sort chemicals into Hazard Classes
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4. Examples
a. Osmium Tetroxide used to stain for electron microscopy (solid)
i. Find LD50 (oral, mice) = 162 mg/kg
ii. Oral Toxicity Table: HC3 “Toxic if Swallowed” and “Danger”
iii. Handle with correct gloves and in a chemical fume hood
b. Methyl Iodide (CH3I) used as a methylating reagent (boiling pt = 42 oC)
i. LD50 (oral, rat) = 76 mg/kg; LC50 (inhalation, rat) = 1.3 mg/L
ii. Oral Toxicity Table: HC3 “Toxic if Swallowed” and “Danger”
iii. Inhalation Toxicity Table: HC2 “Fatal if Inhaled” and “Danger”
iv. Handle with correct gloves and in a chemical fume hood
c. Allyl Alcohol used in synthesis (boiling pt = 97 oC)
i. LD50 (oral, mouse) = 85 mg/kg; LC50 = 165-520ppm; LD50 (dermal, rat) = 45
mg/kg
ii. Oral Toxicity Table: HC3 “Toxic if Swallowed” and “Danger”
iii. Inhalation Toxicity Table: HC2 “Fatal if Inhaled” and “Danger”
iv. Dermal Toxicity Table: HC1 “Fatal in contact with skin” and “Danger”
v. Critically important to wear correct gloves, work in hood, DON’T SPILL
5. TOXNET = National Institutes of Health website for toxicity data
http://toxnet.nlm.nih.gov / ChemIDPlus / Search for Chemical Name / Toxicity
/ Haz-Map / Search for Chemical Name
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6. Assessing Other Acute and Chronic Health Hazards
a. Categories outside of Acute Toxicity don’t have very good data: examples
commonly found in labs given of each highest GHS hazard class
b. GHS Labeling has yet to be implemented, but a sample is shown below
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7. More Examples (Using TOXNET)
a. Carbon Disulfide (S=C=S)
a. LD50 (oral, rat) = 3188 makes is HC5 “Slightly Toxic”
b. bp = 46 oC and vapor pressure = 300 mmHg at 20 oC signals inhalation route
c. LC50 range 10-25 mg/L = 6400ppm is HC4 “Moderately Toxic”
d. Severe skin and eye irritant, easily absorbed through skin
e. Not carcinogenic, Not genotoxic
f. Flash Point = -30 oC = extremely flammable
g. Fume Hood, gloves, no ignition sources
b. Toluene diisocyanate (TDI)
a. LD50 (rat, oral) = 2060 mg/kg is HC5 “Slightly Toxic”
b. LC50 range 0.06-0.35 mg/L is HC1 “Fatal if Inhaled”
c. Powerful irritant, corrosive, respiratory sensitizer, eye damage
d. Many precautions need to be taken
c. Chloromethyl methyl ether (ClCH2OCH3)
a. LD50 (oral, rat) = 500 mg/kg is HC4 “Harmful if Swallowed”
b. LC50 (rat) = 0.18 mg/L is HC1 “Fatal if Inhaled”
c. Potent human carcinogen (HC1 for carcinogens)
d. Causes second degree burns to skin (HC1 for corrosives)
e. Gloves, fume hood, lab coat
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C. Section 6.2.2 Occupational Exposure Limits
1.
Incident 6.2.2.1 Mercury Poisoning in an Academic Lab
2.
Goals
a. Understand what OEL’s are (Occupational Exposure Limits)
b. Understand how to use them to assess relative risk of hazards
c. Most lab settings will never approach OEL’s: for industry, lots of compound
i. May exceed OEL if you don’t use a hood
ii. May exceed OEL if you spill a chemical
3. Acronyms
a. ACGIH = American Conference of Governmental Industrial Hygienists
i. Not a government body
ii. OSHA (Occupational Safety and Health Administration) often uses their #’s
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b. TLV = Threshold Limit Values
i. Recommendations, not mandatory limits (unless OSHA says they are)
ii. Airborne concentration limits (unless otherwise noted)
iii. Estimates for TWA (Time Weighted Average) value an employee can be
exposed to (5d/w, 8h/d)
iv. Assumes 150 pound male between 25-44 years old
v. TLV ± 10% not considered inherently safe/unsafe (wiggle room)
vi. Updated listing is published every year
vii. TLV-STEL = Short Term Exposure Limit (max value for 15min exposure)
viii. TLV-C = Ceiling level (not to be exceeded at any time)
c.
PPM = Parts Per Million
i. Common way to express concentrations used in TLV’s
ii. 1.5 teaspoons of oil added to a gasoline tanker truck (2000 gallons)
iii. 1 molecule out of 1,000,000 molecules is the solute
d. PEL = Permissible Exposure Limit
i. Usually the same as the original TLV’s (1972)
ii. Legal limits which can result in fines if exceeded
iii. TLV’s often more strict, because they are updated yearly
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4. Using TLV’s and/or PEL’s to Assess Hazards
a. Usually only found for chemicals common to industry (about 500 listed)
b. TOXNET lists many of these values
c. NIOSH Pocket Guide to Chemical Hazards lists them
i. REL = NIOSH “Recommended Exposure Level”
ii. IDLH = Immediately Dangerous to Life or Health = maximum concentration
to be exposed to for 30 minutes without irreversible health effects
iii. Registry for the Toxic Effect of Chemical Substances (RTECS)—periodical
d. NO2 Example
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D. Section 6.3.1 Assessing Chemical Exposure
1.
Incident 6.3.1.1 Laboratory Exposure to Solvents
2.
Why and When to Sample
a. Constant Sampling is rarely required
i. Oxygen levels in confined spaces
ii. CO in homes using commercial detectors
iii. Radioactive materials used in a lab on a regular basis
iv. Costly, inconvenient, and unnecessary most of the time
b. OSHA requires only when reasonably expected to exceed safety level
3. Air Sampling in Assessing Chemical Exposure
a. Old School: canaries in coalmines
b. Active Samplers: draw air in with a pump
c. Passive Samplers: rely on diffusion from air with no pump
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d. Sorbent Tubes: chemical is adsorbed onto a medium—charcoal, silica gel, etc…
i. Open by snapping off sealed end
ii. Air is drawn in for a set amount of time
iii. Example: 200 ml/min for 4 hours
iv. Tube is capped and sent for analysis
v. Desorb with flow into a gas chromatograph: ppm reported
e. Impingers: active samplers using a liquid adsorbent
d. May be placed in a pump to pull air through the liquid
e. Analyzed as is the sorbent tube
4. Biological Monitoring
a. Measuring parent chemical and its metabolites in blood, urine, etc…
b. Often used to confirm exposure to a chemical: air was contaminated, was it inhaled
c. Expensive and inconvenient, but gives actual body concentrations
d. Dimethylmercury Poisoning Example
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E. Section 6.3.2 Working or Visiting a New Lab
1.
Incident 6.3.2.1 Nitric Acid Splash in the Face
2.
Surveying the Scene at a New Lab
a. Scene Survey by Emergency Responders
i. Firefighter assesses what is on fire, probability of occupants, weather, etc…
ii. EMT assesses number of patients, power lines down, will car catch on fire
b. New Lab Worker should also do a Scene Survey
i. Introductory Lab: few chemicals, much safety equipment, few hazards
ii. Research Lab: many questions and observations should be made
Many chemicals, hoods, benches, instruments, people
What are the special hazards of the chemicals in the hood?
What kind of fire extinguisher will you need?
Where is the eye wash station and safety shower? Exits?
What kind of Personal Protective Equipment do you need? Where is it?
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F. Section 6.3.3 Safety Planning for New Experiments
1.
Incident 6.3.3.1 Large Scale Reaction Out of Control
2.
Safety Planning must be BEFORE THE EXPERIMENT
a. Recognize the hazards in the new experiment
b. Assess the risks and make changes if too risky
c. Minimize the hazards by using appropriate techniques, equipment, behavior
d. Prepare for emergencies likely to be encountered
3. Checklist
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