UNIT 9

SUPPLEMENTARY HYGIENE SAMPLING

AND COMPLIANCE INFORMATION

BASIC DESCRIPTION OF VARIABLES USED IN HYGIENE

CALCULATIONS AND SAMPLING CONSIDERATIONS

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

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

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 diff erence to calculate duration

SAMPLE DURATION

The volume collected can be determined by using the sample flow rate and sample duration

NOTE: 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

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 (µg) nanograms (ng)

MASS OF SUBSTANCE

Concentration of a substance is calculated using the volume collected (previously calculated) and the mass reported by the laboratory

Incorporating flow-rate formula we get an overall formula:

CONCENTRATION

Sample ID

Start Time

End Time

Sample Duration(min)

Pre flow rate (l/min)

Post flow rate (l/min)

Average flow rate(l/min)

2001 8:02 4:20 1.998 1.967

2051 8:05 4:01 1.965 1.725

2053 9:10 4:32 1.971 1.968

SAMPLE CALCULATION (STEP 1: CALCULATE SAMPLE DURATION/FLOW

RATE)

= (4:20 pm – 8:02 am) = (16:20 – 8:02) = 8 hours + 18 min = 480 min + 18 min = 498 minutes

Where,8 hours * (60 min/hour) = 480 min

SAMPLE CALCULATION (STEP 1: CALCULATE SAMPLE DURATION/FLOW

RATE)

Sample ID

Start Time

End Time

Sample Duration (min)

Pre flow rate (l/min)

Post flow rate (l/min)

Average flow rate(l/min)

2001 8:02 4:20 498 1.998 1.967

2051 8:05 4:01 476 1.965 1.725

2053 9:10 4:32 442 1.971 1.968

= (1.998 l/min + 1.967 l/min) 2= (3.965 l/min) / 2= 1.982 l/min

𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒=(𝑝𝑟𝑒 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒+𝑝𝑜𝑠𝑡 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒)

2

Take smaller fl ow rate and multiply by 10%/5%: 1.967 l/min * 0.1 = 0.197 l/min

Check to ensure other fl ow rate is within 10% 1.967 l/min + 0.197 l/min = 2.164 l/min (OK)

Check fl ow rate within 5% 1.967 l/min * 0.05 = 0.098 l/min + 1.967 l/min = 2.065 l/min (OK)

Sample ID

Start Time

End Time

Sample Duration (min)

Pre flow rate (l/min)

Post flow rate (l/min)

Average flow rate(l/min)

2001 8:02 4:20 498 1.998 1.967 1.982

2051 8:05 4:01 476 1.965 1.725 1.845

2053 9:10 4:32 442 1.971 1.968 1.970

SAMPLE CALCULATION (STEP 2: CHECK FLOW RATES WITHIN 10 & 5

%)

Pre and post flow rates for samples 2001 and 2053 are within 5% of each other Valid Samples

Pre and post flow rates for sample 2051 are not within 10% of each other invalid sample (Throw out)

SAMPLE CALCULATION (STEP 2: CHECK FLOW RATES WITHIN 10 & 5

%)

Sample ID

Start Time

End Time

Sample Duration (min)

Pre flow rate (l/min)

Post flow rate (l/min)

Average flow rate (l/min)

2001 8:02 4:20 498 1.998 1.967 1.982

2051 8:05 4:01 476 1.965 1.725 1.845

2053 9:10 4:32 442 1.971 1.968 1.970

= (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)

Sample ID

Sample Duration (min)

Average flow rate (l/min)

Volume (liters)

Volume (m3)

Mass (mg)

Concentration (mg/m3)

2001 498 1.982

2051 476 1.845

2053 442 1.970

= (2.54 mg)/(0.987 m3)= 2.57 mg/m3

SAMPLE CALCULATION (STEP 4: CALCULATE CONCENTRATION mg/m3)

Sample ID

Sample Duration (min)

Average flow rate (l/min)

Volume (liters)

Volume (m3)

Mass (mg)

Concentration (mg/m3)

2001 498 1.982 987 0.987 2.54

2051 476 1.845 Na Na Na

2053 442 1.970 871 0.871 1.89

*Na = Not applicable

SAMPLE CALCULATION (FINAL CONCENTRATIONS)

Sample ID

Sample Duration (min)

Average flow rate (l/min)

Volume (liters)

Volume (m3)

Mass (mg)

Concentration (mg/m3)

2001 498 1.982 987 0.987 2.54 2.57

2051* 476 1.845 Na Na Na Na

2053 442 1.970 871 0.871 1.89 2.17

FIELD BLANKS

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 fi eld blanks? To test for contamination of samples during transportation, handling,

and storage

How many fi eld 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

What do you do if mass is reported on field blanks? 1. 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

2. 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

3. Ignore contamination and include all samples It is recommended not to use this option bad practice

HOW TO TREAT FIELD BLANK RESULTS

COMMON REASONS PEOPLE DO NOT TAKE FIELD BLANKS

1. Don’t know they should Many people taking hygiene samples lack training on proper

sampling collection procedures and best practices

2. 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 reputation viewed as doing “bad job”/inadequate performance

Feel like all the work was done for nothing not completing tasks

3. Budget restraints Often budgets for hygiene sampling is very limited and people do

not want to allocate a significant proportion (~10%) to “blanks”

What does it mean if we fi nd 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 fi eld blanks) We can overestimate exposures May lead to:

1. Additional sampling (probably more costly than including 10% blanks)

2. Implementation of potentially unnecessary controls (very costly)

3. Workers’ compensation orders for non-compliance

In summary, fi eld blanks: Increases our confidence in our measurements Saves time and money

HOW TO ‘SELL’ FIELD BLANKS

LIMIT OF DETECTION

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 diffi cult to deal with and interpret

LOD DEFINITION

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

DETERMINING COMPLIANCE FROM

EXPOSURE DATA

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 confi dence limits

For this topic please recall readings from last week that covered confi dence limits and determination of compliance (pg. 510-512 of text) and also readings from this week (pg. 516-517)

DETERMINING COMPLIANCE

The fi rst step to determine compliance is to calculate the upper and lower confi dence 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 “true” 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

Confi dence limits are limits placed around the mean (i.e. average) that represents the amount of uncertainty in our samples

The confi dence 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 confi dence limit ↔ lower confi dence limit) specifi es the range of values in which the true exposure mean may lie at a specifi ed confi dence 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

The confi dence limit method used to determine compliance compares the mean, upper and lower confi dence limits to the exposure limit

If the upper confidence limit is below the exposure limit we can say that we are complaint “on average”

If the lower confidence limit is above the exposure limit we can say that we are not compliant “on 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

Mean

Lower Confidence Limit

COMPLIANCE CHART

Exposure Limit

Conce

ntr

ati

on

Compliant Possibly non-compliant Non-Compliant