60mm paver

Silica Part III: How Much Dust is Too Much?


In our introduction to this series on understanding the OSHA PEL, we described what a PEL is and outlined the three factors which determine the PEL: Air, Dust and Time. Here in part III we’re going to explain the second factor: Dust.

There are a few questions we need to answer about dust:

  • How much dust is produced from cutting materials?
  • How much silica is in that dust?
  • How much dust is too much?

Measuring Dust

Let’s start by figuring out how much dust is released from a common cut. For this example we’ll use a familiar material, a standard 60mm paver.

The typical weight for masonry materials is 145 lbs. per cubic foot, or 65,770 grams. This works out to 38 grams per cubic inch. Remember that, we’re going to use it later.

Now let’s look at the dimensions of the cut we’re making. Our depth of cut is 60mm or 2.36 inches, and our length of cut is 4 inches. If we’re using a standard table saw our blade width plus overcut is 0.125 inches. Multiplying these will give us the volume of material removed in a single cut:

2.36 inches * 4 inches * 0.125 inches = 1.18 cubic inches

If we’re removing 1.18 cubic inches of material, and we know that a cubic inch weighs 38 grams, we can calculate the weight of material removed:

1.18 cubic inches * 38 grams = 45 grams

So in one standard 60mm paver cut using a table saw we are removing 45 grams of material.

Converting to micrograms we can start to understand how much dust we’re talking about in OSHA terms:

45 grams
= 45,000 milligrams
= 45,000,000 micrograms


worker cutting block with dustWe’ve determined that one paver cut releases 45 million micrograms of dust into the air. But not all of that dust is silica.

Our tests have shown an average silica content in masonry materials of +/- 20%. If 20% of that dust is silica, we can calculate silica by weight:

45,000,000 * 20% = 9,000,000 micrograms

Through these calculations we now know that 9 million micrograms of respirable crystalline silica is released into the environment in one paver cut.

Great, so what does that mean?


Looking again at the current OSHA PEL:

50 micrograms of respirable crystalline silica per cubic meter of air, or:

50 μg/m3

In other words, for every cubic meter of air a guy breathes, he’s allowed to inhale 50 micrograms of silica.

Let’s go back to part II of this series, where we learned that an average male working at a moderate pace breathes 16.8 cubic meters of air in an eight-hour day. At 50 micrograms for every cubic meter, that means a guy is allowed to breath 840 micrograms in a day within the current OSHA PEL.

And one standard paver cut releases 9 million micrograms.

That’s enough silica to exceed 10,714 days worth of dust exposure.

Using our example, if you were to breathe 100% of the dust from one single paver cut, you’d be breathing over 29 years worth of silica in the OSHA PEL.

We don’t recommend doing that.

So What

Considering these numbers, smart and responsible contractors should understand how dust is measured, how much is too much, and how much their workers are being exposed.

In this example we’ve learned how much silica is produced from a single paver cut relative to the current OSHA PEL. While we know how to calculate the amount of dust being released, we still need to figure out how much of that dust your workers are being exposed to.

The last factor we need to consider is time. For how much time can workers cut, at what level of exposure, and still be within the OSHA PEL?

You’ll have to read Part IV in our series on Understanding the OSHA PEL.

Visit our Silica Dust Home Page. Also check out our dust control power cutters and learn more about what they can do for you and your health.

Previous articles in this series:
Silica Part I: What Contractors Should Know About the OSHA PEL
Silica Part II: The OSHA PEL in Simple Terms

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Comments 12

  1. Please run one musing a skil saw to cut hardie panel over 8 ft or 6 piece of lap siding stacked on a chop saw! Please is really like to know and I think people need to be informed this way

  2. Cutting hardiplank with electric saw,,used respirator part time. Couldn’t s see with mask and safety glasses
    Wegeners vasculitis followed have RA factor

  3. I am cutting, grinding and sanding natural Stone, Flint, quartz.was doing it for days before wearing gloves and mask, then for a couple weeks before wearing more of a respirator mask. What are the hazards.

  4. Hello, please help im a bit worried. I cut a hardibacker cement board inside bathroom with a circular saw and didnt know much about the dust. I continued to work in that bathroom for another 6-7 hours. At the end i used a vacuum, but it brought dust up. The next day i used a vacuum as well. Also i used a circular saw to cut outside. What should i do? i just learned about silica dust. How much did i breath in? Chances i already have silicosis? Thank you

  5. I recently dry swept a room of about 500 sq ft. The floor was moderately covered in concrete dust and wood chips and I was only bearing an N95 half mask. The rooms main entrance was covered with a large floor to ceiling tarp and I had two windows open at the opposite side of the room. When I thought the dust had settled I sat in that room to eat. I was in that area from start to Finnish about an hour or maybe just over. What risk am I at for developing any Silica related issues?

  6. This has to be the most messed up thing I’ve ever heard about. When I was younger, people told me to shrug off breathing in this dust, little did I know, it’s not only incurable, it’s also fatal (at the smallest doses). Here I am, never having worried about this before, suddenly having trouble breathing, from drilling 3 tiny holes in a ceiling. What I’m reading about it is that I’ll be dead in the next few months. I thought I had to watch out for sun exposure, but that’s nothing compared to this. Needless to say, I’ll be creating awareness of this as much as I can the coming days, never did I ever think, that something so easily prevented, would kill me so suddenly at the prime of my life. Let that be a lesson too, don’t ever trust anyone when they say they know what they are talking about. Here’s to hoping for semi-good news at the doctor’s office tomorrow. Farewell.

  7. James, I had a similar experience a few days ago and am worried, too.
    How have things progressed with you? Are you okay? Any symptoms? Visits to doctor?

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