October 28, 2026
This week’s photo is courtesy of- Western Hydro Engineering- Cochise, AZ, USA .
Safety Focus
Part 3 of 4: Respiratory Protection Program
A respirator only works if air goes through the filter, not around it. That is what fit testing, seal checks, and care are for.
Fit testing. Anyone wearing a tight-fitting facepiece is fit tested before first use, whenever a different facepiece (size, style, model, or make) is used, and at least once a year after that. A new test is also required when changes such as facial scarring, dental changes, or an obvious change in body weight could affect the fit. A qualitative test (the pass or fail taste or smell test) may only be used for negative-pressure air-purifying respirators that need a fit factor of 100 or less. A quantitative test measures the fit; passing is a fit factor of at least 100 for a half facepiece and 500 for a full facepiece.
The seal. The standard does not allow tight-fitting respirators on anyone whose facial hair, or anything else, comes between the seal and the face. And a user seal check is required every time the respirator goes on.
What the mask can do. OSHA assigns a protection factor of 10 to a half-mask air-purifying respirator and 50 to a full facepiece. In plain terms, a properly fitted and used half mask is expected to cut the exposure inside the mask to about one-tenth of the air outside. That is why a bad fit matters so much.
Filters and cartridges. For dusts, the filter must be NIOSH-certified. For gases and vapors, the standard's answer is not "change it when you smell it." The cartridge needs a NIOSH-certified end-of-service-life indicator, or the employer sets a change schedule based on objective data so cartridges come out before they are spent.
Leave the area. The employer must ensure workers leave the respirator area to wash the face or facepiece, to replace the respirator or its filters or cartridges, or if they detect breakthrough, a change in breathing resistance, or leakage.
Care. Respirators used routinely are inspected before each use and during cleaning, and cleaned and disinfected per the standard's Appendix B-2.
Key Takeaways:
• Fit test before first use, with any change in facepiece, after physical changes that could affect fit, and at least annually; seal check every time it goes on.
• No tight-fitting respirator where facial hair sits under the seal.
• Half mask APF 10, full facepiece APF 50, only when the fit is right.
• Gas and vapor cartridges run on an end-of-service-life indicator or a change schedule, not your nose.
Sources:
Knowledge Share
Part 3 of 4: Formation Sieve Analysis
Tuesday you read a curve. Today you build one, in the order you would work it on the bench.
1. Size the sample. A Bureau of Reclamation study found the minimum test specimen should weigh 100 times the mass of the largest particle in it. Coarse material needs a bigger sample. To keep it simple, assume you need a sandwich bag size sample.
2. Dry and weigh it. That starting dry weight is the number everything else is measured against.
3. Stack and shake. Nest the sieves coarsest on top down to the pan, shake, and weigh what stays on each sieve.
4. Do the math. Here is a 500-gram illustrative sample, the same one plotted Tuesday:
Sieve (opening) | Retained (g) | Cumulative retained | Percent passing |
#8 (.0937") | 10 | 2% | 98% |
#16 (.0469") | 50 | 12% | 88% |
#30 (.0234") | 140 | 40% | 60% |
#40 (.0165") | 95 | 59% | 41% |
#50 (.0117") | 85 | 76% | 24% |
#100 (.0059") | 95 | 95% | 5% |
#200 (.0029") | 20 | 99% | 1% |
Pan | 5 | 100% | 0% |
Cumulative retained is the running total divided by 500. Percent passing is 100 minus that. The masses add back to 500 grams. If yours do not come close to the starting weight, find out why before you plot.
5. Plot and read. Grain size goes on a log scale, percent on the other axis. Connect the points, then read D10 and D60 where the curve crosses 10 and 60 percent passing. For this sample, D60 is .023", D10 is about .007", and Cu is about 3.3.
What this means for your operation:
• Size each sample to the coarsest material in it.
• Check that the retained weights add back to the starting weight before trusting the curve.
• When a lab runs the analysis, ask for the raw weights and whether the sample was washed.
Sources:
• U.S. Bureau of Reclamation: Minimum Test Specimen Mass for Gradation Analysis (GR-88-2)
Recommended Print References:
• Hydraulics of Wells: American Society of Civil Engineers
• Handbook of Ground Water Development- Roscoe Moss Company
• Groundwater & Wells, Third Edition- Edited by Robert J. Sterrett, Johnson Screens
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