Unit 9 hygiene calculations sampling issues compliance
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Unit 9 hygiene calculations sampling issues compliance Presentation Transcript

  • 1. Unit 9Supplementary hygiene Sampling and compliance information
  • 2. Basic description of variables used in hygiene calculations and sampling considerations
  • 3. Flow rate is the rate of which air is being pulled through the sampling device
    Typically reported as liters/min (l/min)
    Calculate average between pre and post calibration measures
    π‘“π‘™π‘œπ‘€π‘Ÿπ‘Žπ‘‘π‘’=(π‘π‘Ÿπ‘’Β π‘“π‘™π‘œπ‘€π‘Ÿπ‘Žπ‘‘π‘’+π‘π‘œπ‘ π‘‘Β π‘“π‘™π‘œπ‘€π‘Ÿπ‘Žπ‘‘π‘’)2
    NOTE on calibration:
    Pre and post measurements must be within 10% or sample is invalid and should be thrown out
    If >5% but <10%, sample may be considered with caution
    Flow Rate
  • 4. Sample duration is the total length of time the sample was collected
    Typically this is reported in minutes (min) but can also be reported in seconds, hours, days, or weeks
    During measurement record the (1) start time and date when sampling begun, (2) the end time and date when sampling ceased
    Take the difference to calculate duration
    π‘‘π‘’π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘›=Β π‘’π‘›π‘‘Β π‘‘π‘–π‘šπ‘’Β βˆ’π‘ π‘‘π‘Žπ‘Ÿπ‘‘Β π‘‘π‘–π‘šπ‘’
    Sample duration
  • 5. The volume collected can be determined by using the sample flow rate and sample duration
    π‘£π‘œπ‘™π‘’π‘šπ‘’=π‘“π‘™π‘œπ‘€Β π‘Ÿπ‘Žπ‘‘π‘’Β βˆ—π‘‘π‘’π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘›
    π‘£π‘œπ‘™π‘’π‘šπ‘’Β π‘™π‘–π‘‘π‘’π‘Ÿπ‘ =π‘™π‘–π‘‘π‘’π‘Ÿπ‘ π‘šπ‘–π‘›π‘’π‘‘π‘’βˆ—π‘šπ‘–π‘›π‘’π‘‘π‘’π‘ 
    π‘£π‘œπ‘™π‘’π‘šπ‘’Β π‘™π‘–π‘‘π‘’π‘Ÿπ‘ =π‘™π‘–π‘‘π‘’π‘Ÿπ‘ π‘šπ‘–π‘›π‘’π‘‘π‘’βˆ—π‘šπ‘–π‘›π‘’π‘‘π‘’π‘ 
    Volume will most likely need to be converted to m3, which can be done either before entering into concentration equation or after
    Volume Collected
    If we multiply the flow rate by duration we can see that we cancel out minutes and are left with liters
  • 6. For most analytical methods we will be provided with a mass value from the analytical laboratory that conducted the analysis of the samples
    The units will depend on the measurement method
    Common unit values would include:
    grams (g)
    milligrams (mg)
    micrograms (Β΅g)
    nanograms (ng)
    Mass of substance
  • 7. Concentration of a substance is calculated using the volume collected (previously calculated) and the mass reported by the laboratory
    πΆπ‘œπ‘›π‘π‘’π‘›π‘‘π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘›=π‘šπ‘Žπ‘ π‘ π‘£π‘œπ‘™π‘’π‘šπ‘’=π‘šπ‘”π‘™π‘–π‘‘π‘’π‘Ÿ
    Incorporating flow-rate formula we get an overall formula:
    πΆπ‘œπ‘›π‘π‘’π‘›π‘‘π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘›=π‘šπ‘Žπ‘ π‘ π‘“π‘™π‘œπ‘€π‘Ÿπ‘Žπ‘‘π‘’βˆ—π‘‘π‘’π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘›=π‘šπ‘”π‘™π‘–π‘‘π‘’π‘Ÿπ‘ π‘šπ‘–π‘›π‘’π‘‘π‘’βˆ—π‘šπ‘–π‘›π‘’π‘‘π‘’π‘ 
  • 8. Sample calculation (step 1: Calculate sample duration/flow rate)
    π‘¬π’™π’‚π’Žπ’‘π’π’†Β π‘Ίπ’‚π’Žπ’‘π’π’†Β π‘°π’…Β πŸπŸŽπŸŽπŸ
    π‘‘π‘’π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘›=Β π‘’π‘›π‘‘Β π‘‘π‘–π‘šπ‘’Β βˆ’π‘ π‘‘π‘Žπ‘Ÿπ‘‘Β π‘‘π‘–π‘šπ‘’
    = (4:20 pm – 8:02 am)
    = (16:20 – 8:02)
    = 8 hours + 18 min
    = 480 min + 18 min
    = 498 minutes
    8 hours * (60 min/hour) = 480 min
  • 9. Sample calculation (step 1: Calculate sample duration/flow rate)
    π‘¬π’™π’‚π’Žπ’‘π’π’†Β π‘Ίπ’‚π’Žπ’‘π’π’†Β π‘°π’…Β πŸπŸŽπŸŽπŸ
    = (1.998 l/min + 1.967 l/min)
    = (3.965 l/min) / 2
    = 1.982 l/min
    π‘“π‘™π‘œπ‘€π‘Ÿπ‘Žπ‘‘π‘’=(π‘π‘Ÿπ‘’Β π‘“π‘™π‘œπ‘€π‘Ÿπ‘Žπ‘‘π‘’+π‘π‘œπ‘ π‘‘Β π‘“π‘™π‘œπ‘€π‘Ÿπ‘Žπ‘‘π‘’)2
  • 10. π‘¬π’™π’‚π’Žπ’‘π’π’†Β π‘Ίπ’‚π’Žπ’‘π’π’†Β π‘°π’…Β πŸπŸŽπŸŽπŸ
    Take smaller flow rate and multiply by 10%/5%:
    1.967 l/min * 0.1 = 0.197 l/min
    Check to ensure other flow rate is within 10%
    1.967 l/min + 0.197 l/min = 2.164 l/min (OK)
    Check flow rate within 5%
    1.967 l/min * 0.05 = 0.098 l/min + 1.967 l/min = 2.065 l/min (OK)
    Sample calculation (step 2: Check flow rates within 10 & 5 %)
  • 11. Pre and post flow rates for samples 2001 and 2053 are within 5% of each other οƒ  Valid Samples
    Pre and post flow rates for sample 2051 are not within 10% of each other οƒ  invalid sample (Throw out)
    Sample calculation (step 2: Check flow rates within 10 & 5 %)
  • 12. π‘¬π’™π’‚π’Žπ’‘π’π’†Β π‘Ίπ’‚π’Žπ’‘π’π’†Β π‘°π’…Β πŸπŸŽπŸŽπŸ
    π‘£π‘œπ‘™π‘’π‘šπ‘’=π‘“π‘™π‘œπ‘€Β π‘Ÿπ‘Žπ‘‘π‘’Β βˆ—π‘‘π‘’π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘› = (1.982 l/min * 498 min)
    = (1.982 l/min * 498 min)
    = 987 liters
    Convert to m3 = 987 liters * (1 m3/1000 l)
    = 0.987 m3
    Sample calculation (step 3: Calculate volume m3)
  • 13. π‘¬π’™π’‚π’Žπ’‘π’π’†Β π‘Ίπ’‚π’Žπ’‘π’π’†Β π‘°π’…Β πŸπŸŽπŸŽπŸ
    πΆπ‘œπ‘›π‘π‘’π‘›π‘‘π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘›=π‘šπ‘Žπ‘ π‘ π‘£π‘œπ‘™π‘’π‘šπ‘’Β Β Β Β =π‘šπ‘”π‘š3
    = (2.54 mg)/(0.987 m3)
    = 2.57 mg/m3
    Sample calculation (step 4: Calculate concentration mg/m3)
  • 14. *Na = Not applicable
    Sample calculation (Final concentrations)
  • 15. Field blanks
  • 16. Field blanks are samples that are sent out during sampling that are opened and closed without pulling air through them
    What is the purpose of field blanks?
    To test for contamination of samples during transportation, handling, and storage
    How many field blanks should you use?
    It depends but recommended practice is 10% of your number of samples
    Do we have to analyze the samples?
    YES you must! Best practice
    Field blanks
  • 17. What do you do if mass is reported on field blanks?
    Throw the samples out for that sampling period
    Good option if contamination is limited to small number of samples or if contamination levels were high
    Adjust for the contamination
    Acceptable if contamination levels are not too high
    If small batch is contaminated we can adjust only those samples from the contaminated batch by the field blank value
    If contamination is on multiple blanks during a sampling project we can adjust for each batch or we can apply an adjustment to all samples using average field blank value
    Ignore contamination and include all samples
    It is recommended not to use this option οƒ  bad practice
    How to treat Field blank results
  • 18. Common Reasons people do not take Field blanks
    Don’t know they should
    Many people taking hygiene samples lack training on proper sampling collection procedures and best practices
    Don’t want to risk having to throw out samples
    Perceived risk of job
    Can be regarded as throwing money away in eyes of management
    Risk of reputationοƒ  viewed as doing β€œbad job”/inadequate performance
    Feel like all the work was done for nothing οƒ  not completing tasks
    Budget restraints
    Often budgets for hygiene sampling is very limited and people do not want to allocate a significant proportion (~10%) to β€œblanks”
  • 19. What does it mean if we find contamination in our blanks?
    We may potentially have contamination in our samples
    Our reported results may be higher than the actual exposure levels
    By having blanks we are aware of contamination and can adjust accordingly
    What does it mean if we had contamination and do not know (i.e. we don’t have field blanks)
    We can overestimate exposures
    May lead to:
    Additional sampling (probably more costly than including 10% blanks)
    Implementation of potentially unnecessary controls (very costly)
    Workers’ compensation orders for non-compliance
    In summary, field blanks:
    Increases our confidence in our measurements
    Saves time and money
    How to β€˜sell’ field blanks
  • 20. Limit of detection
  • 21. What is LOD?
    LOD stands for the Limit Of Detection
    This is the lowest level (e.g. concentration) measureable by an analytical method or sampling device
    Why is this important
    Measurements under the LOD do not give us much information on the hazard but they cannot be ignored/omitted from analysis or the discussion of results
    Having multiple LOD measurements often results in skewed or lognormal data distributions
    They can be difficult to deal with and interpret
    LOD Definition
  • 22. Several methods have been proposed, most important thing to remember is you cannot omit them from determining the average concentrations. Two most commonly used:
    Method 1
    Multiply the LOD by 0.5 (i.e. LOD/2) for each data point that was <LOD
    For example if the LOD reported is 2 ppm then you would input (2ppm*0.5 = 1ppm)
    Only use when the data are highly skewed (GSD approximately 3.0 or greater)
    Method 2
    Multiply the LOD by 0.707 (i.e. LOD/√2) for each data point that was <LOD
    For example if the LOD reported is 2 ppm then you would input (2ppm*0.707 = 1.4 ppm)
    Use when data not highly skewed
    Methods to deal with <lod measurements
  • 23. Determining compliance from exposure data
  • 24. Now that we have conducted sampling how do we determine if we are compliant with the regulations?
    Do we compare each reading/sample with limits?
    Do we calculate the % of samples over the limits?
    Do we compare the average of the readings/samples with the limits?
    Although these methods are commonly used compliance is a bit more complex and methods for determining compliance are under debate
    For this class we are going to review a method frequently used and accepted in North America using confidence limits
    For this topic please recall readings from last week that covered confidence limits and determination of compliance (pg. 510-512 of text) and also readings from this week (pg. 516-517)
    Determining compliance
  • 25. The first step to determine compliance is to calculate the upper and lower confidence limits of the mean
    Why do we do this?
    When we take samples we introduce uncertainty/error into our measurement
    This comes from error in our measurement, instruments, and analysis
    This means the measurement we take is not the β€œtrue” value of the exposure
    The true value is the measured exposure +/- error
    Calculating confidence limits (or the confidence interval) allows us to account for some of the error/uncertainty in our measurements
    Determining compliance using confidence limits
  • 26. Confidence limits are limits placed around the mean (i.e. average) that represents the amount of uncertainty in our samples
    The confidence limits include an upper and a lower bound estimate:
    LCL = lower confidence limit, the lower bound limit
    UCL = upper confidence limit, the upper bound limit
    This interval (upper confidence limit ↔ lower confidence limit) specifies the range of values in which the true exposure mean may lie at a specified confidence level (95% most common)
    More narrow the interval, the more precise our measurements are
    More wide the interval, the less precise our measurements are
    Confidence limits
  • 27. The confidence limit method used to determine compliance compares the mean, upper and lower confidence limits to the exposure limit
    If the upper confidence limit is below the exposure limit we can say that we are complaint β€œon average”
    If the lower confidence limit is above the exposure limit we can say that we are not compliant β€œon average”
    If the lower and upper confidence limit crosses the exposure limit it is unclear if we are compliant or not and require further testing
    Using confidence limits to determine compliance
    The next slide graphically displays the concept where:
    Upper Confidence Limit
    Lower Confidence Limit
  • 28. Compliance chart
    Exposure Limit
    Compliant Possibly non-compliant Non-Compliant