Industrial Hygiene in Construction

Controlling most of these types of exposures is really simple. If you know the job- and you know it will generate airborne silica = Pre Task Plan!

I wish Superintendents would enforce their project managers, or project engineers, to make a pre-task plan for every concrete/silica producing task. Then, (please don’t stop yet), review the plan once the project starts!

Below are two examples with different outcomes:

1. Cutting concrete block.

The pretask plan called for a garden hose with attachment(s) to wet the cutting area. Everything was perfect until the water was shut off. But, they improvised and found an electric water pump with bucket and recycled the water. It was a great outcome. What if the power went out? They could have used a Hudson sprayer.

2. Grinding plaster off a brick wall.

They built an enclosure and containment. They had a negative air machine with HEPA filters. They had a vacuum with HEPA filters, tyvek, 1/2 face respirator, eye protection, etc. But, as they worked the vacuum couldn’t keep up with the amount of dust generated by the 7 inch Bosch grinder. It was really dusty. They worked like this for days. No one onsite saw them because they were in containment. Unfortunately  the project is almost over and it could have been better. A simple shroud to the grinder, like this one (no endorcement) might have controlled the dust & silica. Sure, it might have been troublesome to find the exact one, and get a vacuum attachment, and have the extra weight, and ….

So, let’s talk to people about silica, talk about solutions, and then check to see if they’re effective.

If you operate a ready-mix plant and have concrete trucks, you are aware of this process. Once a year (hopefully, only once) a person must climb into the drum of the ready-mix truck and chip off excess concrete. What happen during regular use, is that some concrete hardens, which usually sets-up over and around the blades. Access into the drum is by either the 3×4 hole in the side, or down the chute.

Yes, it is a confined space (def’n: 1. large enough to enter, 2. not designed for occupancy, and 3. limited entry/egress).

Here are a list of the possible hazards:

• silica dust (from chipping concrete)
• noise exposure
• hazardous atmosphere (curing concrete uses up oxygen, which we DO need BTW)
• slipping hazard (drum is round inside)
• heat stress (if you’re trying to do this activity in the summer)
• eye hazard (chipping)
• electrical hazard (if you’re using water & have an electric hammer)
• lock out / tag out (if the truck drives away, or if the barrel starts turning)

There are many resources available (see below). Some things to keep in mind; ventilation (fans, etc) to control the airborne silica dust are usually not effective (too much dust versus exhaust). Water controls are best, but you must limit the amount of water and the direction of the sprayer. I suggest looking at what others have done.

Keep in mind, if you perform this activity you will need (as a company):

• respiratory program (medical, fit test, written plan)
• confined space program (multi gas meter, written program, attendant?)
• lock out /tag out policy or procedures
• training (for each of the above, and for this specific activity)

At this point I know what my contractor-friends are thinking…I will subcontract this out!   ha. If you do, please make sure your sub is doing it right.

Resources:

Georgia Tech – good presentation & guidance

Georgia Tech/OSHA – Safe Work Practices (in Spanish too!)

Teamsters H&S hazards & controls

Illinois DCEO – Consultation on ready mix cleaning

When performing air monitoring it can be useful to take multiple samples on the same individual throughout the day. Here are some reasons to change out the filters:

• build up of dust on filter – can cause overloading
• break-out the exposure data. Morning versus afternoon, or by job tasks, or the physical area the employee is working in, controls vs. no-controls, etc.
• if you question the employees motives. If you think the employee might skew the results, multiple samples might give you better control- or at least tell you if one is way-out-of-line.

Once you have your data results, how do you combine them?

If you’re taking particulate (dust, lead, cadmium, silica, etc) and you have the concentrations (from the lab) here is what to do.

1. note the time (in minutes!) and the concentration results (mg/m3, ug/m3, etc) for each sample
2. multiply the time and concentration for each – then add each number together
3. finally, divide the above number by the total number of minutes sampled. This is your time weighted average (TWA).

Simple?! Yes. …And it’s really easy to make a mistake too. Check your math, and then eyeball the results and see if they make sense logically.

Here’s an example:

Andrew took three samples during one shift while Shelley was rivet busting through leaded paint. The first sample (118 minutes) was reported as 6.8 ug/m3 of lead, the second was for 245 minutes and had a concentration of 18 ug/m3. The last sample was taken for 88 minutes and was reported a level of 29 ug/m3. The overall results is 17.2 ug/m3 for the total time sampled. (Side: if you sampled for their entire exposure, and they worked longer hours, you could add those hours (assuming zero exposure) into the final time-in step three)

See the math below:

The big industrial hygiene conference (AIHCe) is held in a different city each year. This year was Indy, Indiana. Below is my personal top ten list  of “lessons learned” from last week.

1. IH’s need to do a better job of sharing. We don’t share data, experiences, information, knowledge or our ideas well.
2. CPWR is trying to share. Center for Construction Research & Training.  I’m looking forward to seeing their published independent review of local exhaust ventilation (LEV) units.
3. The minimum exhaust rate for a portable exhaust unit must be 106 cfm (cubic feet per min) to capture particulates (dust, silica) during tuckpointing with a 5 in grinder (but it’s also a good rule of thumb).
4. Asphalt milling machines are still a huge silica problem. Water controls are NOT enough. You need a local exhaust system too. (here’s an earlier post I made on it)
5. GHS Safety Data Sheets – it’s not as complicated as you think. There are some significant changes, but don’t worry, OSHA’s here to help (ha). Seriously, more information will be available soon.
6. Ignite. Have you seen these before? Short, stand up speeches about their ideas/passions. Similar to TED. Some were better than others. But, did I mention they were short?
7. Committees. Be careful when you open your mouth. My idea was so great, they are making me do it.
8.  ANSI A10.49! A health standard for construction. Great idea, but lots of work.
9. Check out Environment for Children. I don’t know much about it, but they have a great mission.  Believe me, in the US, we’re WAY ahead.
10. Presentation. It’s all up to you to make it. I will not cast blame on those who had bad presentations. BUT, it reminds me that I should work on this skill. Even if you have something good to say, if you give a horrible presentation, it’s likely no one will notice. On the other side, if your presentation is good, people will listen, even if you’re talking about nothing!  My favorite of the week: Dr. Mike Morgan (Univ. of Washington) on Chromium VI. He was very factual, not too flashy, and make the point without needless details.

‘Tis the season for silica (here, and here too).

I had four observations about this picture,

1. paper dust masks are totally inadequate for this task, and
2. why isn’t there any engineering controls (water?, vacuum?), and
3. why is the observer standing in the dust plume?, and
4. what does the employees do with their clothes after work?

Please be safe out there.

I had posted a few weeks ago about a recent sighting of silica exposures during concrete/asphalt cutting. Then, today, at a stoplight…there it is.

A worker was using a gas powered hot saw (cut off saw) with an abrasive blade to cut a concrete pipe. No respirator.

If you were me, what would you do? (Leave your answer in the comments section)

• call the company main office?
• stop and caution the employee?
• call OSHA?
• take a picture and post it for the world to see (check…ha)
• offer to buy a respirator
• perform air monitoring for them? (for free, of course.?)

In  the trainings I perform for employers, I try to explain to them that there IS overexposure to silica on their jobsite. I tell them that if I could be at their site everyday, and be ready to perform air monitoring at a moments notice, I could find overexposures.

Here is an example of a road crew cutting asphalt with a concrete saw. I’m sure it was a small cut (since they were not a concrete cutting subcontractor, and it was a tiny little saw). But the haze you see is the dust plume from the cutting.

I just happened to drive by and be stopped at a red light when this occurred. I know, I probably shouldn’t have touched my phone (while in my car) to take a picture…but I couldn’t resist. And, with that same train of thought, the road construction crew probably thought, “it’s just a small cut and it will only take 5 minutes”. So, neither of us are innocent

.

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.