Industrial Hygiene in Construction

If you are taking multiple samples employees to get an average total time weighted average (TWA), here is how you calculate TWAs.

First take the first concentration (mg/m3 or ug/m3, etc.) and multiply it by the time (in minutes). Do this again for each sample. Add each of these calculated amounts together.

Then, divide by the total minutes sampled.

Or, alternatively, by the total time in the work shift (480 minutes for an 8-hour day). You would only do this if you captured all of their exposure and the rest of the day was (in theory) zero additional exposure.

Look at the number. It should make sense and be logical. If not, look at your math, especially the units for each.

If you like math, here’s the formula: 

The question I commonly hear is:

Do I need to wear a respirator while cutting concrete wet? What, if so, what type?

To simple answer is, yes.

If wet concrete cutting is done correctly, you should not need a respirator. However, what happens is that in the field, many variables occur. ((Engineering Controls)) Sometimes the water will be directed at the top of the blade (for cooling, not for dust control). The water must be directed at the cutting site on the blade in order to control dust.

Another variable is ((Administrative Controls)) clean up. Do the workers clean up the wet slurry? Or, do they wait till it’s dry and then use a leaf blower?  Do they vacuum the slurry? What happens when the job is done and the vacuum is in the shop? Does the employee wet it down, or blow it off?

Also, what happens when your worker is cutting wet and the water stops? Does he continue? What about if he get to a curb? Do they get the Stihl hot saw and cut wet? What if they don’t have water for that saw?

So, technically, if done correctly, a respirator should not be needed. However, if you don’t have the protocols, air monitoring data, and management controls in place to do it correctly, get a respirator.

Which respirator, you ask? Minimum would be a tight fitting negative pressure half face with HEPA filters. If they are knowingly performing concrete cutting dry – then it needs to be a full face respirator.

Leaded sheetrock is what the name says, sheetrock with a lead layer. It is used in hospital x-ray rooms and other health office clinics for containing / controlling the emitted x-rays while the machines are in use.

Plastering / Drywall companies who install this type of drywall need to follow the OSHA Construction Rules for lead work. I have heard of airborne exposures being at the exposure limits (50 ug/m3) during the installation due to the cutting and breaking of the drywall. My own personal monitoring has been below the Action Limit (30 ug/m3), but I have consistently found levels above the detection limit. This information should be taken as a caution to others.

For starters the employer will need to provide:

• half face negative pressure tight fitting respirators with HEPA cartridges
• protective clothing (like Tyvek (R))
• containment (for the dust generated)
• training (in lead and respirators)
• hand washing / changing areas
• HEPA vacuums for clean up
• possibly air monitoring (by a qualified industrial hygienist)
• possibly blood lead testing

The sheetrock should be contained during transport. Installation should be performed in a contained area with employees in respirators who are trained and competent. Clean-up should be done with HEPA vacuums. Air monitoring should be performed to assure that employees were adequately protected during their activities.

Working with this type of material is no excuse to cut corners (no pun intended). Protect your employees, the hospital, the patients, and others.

To simplify OSHA’s rules for lead in construction this is how I explain it:

Do you have lead (lead in paint usually) on the construction project? …Then you must comply with the entire rules.

How do you start? You start by listing the tasks where you will disturb the lead. For example, demolition, hand scraping, torch cutting.

After you’ve identified the tasks, then you can look at the OSHA rules and determine the minimum personal protective equipment (PPE) that will be necessary for your employees to wear while they’re performing each individual task.

Next, train your empoyee’s in lead awareness, which is the dangers, prevention and hazards of lead poisoning.

There is one other important aspect. Measuring your airborne levels of lead. This is done by air monitoring with a battery powered pump (and is typically one role of an industrial hygienist). Airborne lead results will indicate if you are generating a lot of lead into the air, or not. If you’re not, you can sometimes downgrade (bad word) the level of respiratory protection for your employees.

• Caveat: this is not a complete summary of the rules. Please know and understand your local and federal rules entirely! This also does not cover the EPA’s Lead Rules which have specific items that you must do.

Most welders wear ear plugs. Why? Because of noise, sure, but also because of slag entering into their ear canal and harming the ear drum.

The average noise levels can vary throughout the day – depending on the project. During the day of this survey, welders were tacking and fabricating stairs and handrails. However, their typical business is large tanks. Do you think the noise levels might vary depending on what they’re making? I do.

I’d also bet that air monitoring during these events would vary. If the welder is inside a large tank performing welding for a few hours, I’d worry about more than just welding fumes. (some might be: welding gases displacing oxygen, electrical hazards, heat exposure, UV, and also the welding metal and rods).

Be safe out there!

When performing spray finishing activities with any product that contains isocyanates (diisocyanates, HDI, MDI, TDI) the minimum respiratory protection to be worn is a powered air supply respirator.

The reasoning is simple: isocyanates DO NOT have good warning properties.

Painters can usually tell when their cartridges are wearing-out, or getting “break through”. However, with isocyanates, the odor threshold is much too high to detect (it can be detected, but only at harmful levels).

In addition, isocyanates have a skin-notation, meaning that if the product gets onto the skin, it can be absorbed. As you can see, this employee was not wearing the proper PPE (personal protective equipment). However, when you’re a consultant, you have temper your comments. We did educate him and also told the general manager of our concerns and the reasoning.

On the plus-side, they had a manometer that was used and the employee knew when to change out the filters.  How this simple meter works is this:  A manometer measures the pressure differential between two different areas. In a paint booth it measures the pressure between each side of the air filters for the air coming into the booth. If the pressure gets too high, then the filters are clogged (or built-up). Notice the arrows on the bottom of the gauge to see when to service the filters. When the manometer (in this case) reads above 0.045 either the fan has to work harder, or the air escapes by the filter (in various ways- more information for another time)

Another week – another rock crusher. ”Tiz the season for the crushing to begin.

This particular rock crusher happened to be located a few miles up the mountain. Which had a great view, but the elevation difference can significantly change your flow rate if you precalibrated the pumps at sea level (which we did). The difference between our pre and post calibration (post calibration was done onsite) had a difference of 1.4%. Not too much, you say, but multiply that times 10 hours of sampling and… that might be significant.

The quick solution is to calibrate onsite. Pre and post. There is a formula you can use to calculate the difference in pressure (due to altitude) but it makes me dizzy just thinking about how to post it on this site.