Unit 9 hygiene calculations sampling issues compliance


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Unit 9 hygiene calculations sampling issues compliance

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