Industrial Hygiene in Construction

No, and maybe yes.

Crystalline silica (the dangerous type) is typically NOT added into precast concrete. On the other hand, Silicon dioxide (also called micro silica, or silica fume) is added for strength, bonding, and compression strength to concrete. It is usually added at the cement factory. This type of silica binds with the portland cement and (from an inhalable particulate standpoint) is not dangerous.

However, danger lies it what ELSE is added to the precast concrete…..ROCKS!

Rocks, dirt and soil contain varying amounts of silica in the Northwest US. And, if these are broken, ground, chipped, hammered, they can become airborne….which allows the crystalline silica to be released and THAT is dangerous.

Always use wet methods when working with precast concrete.

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.

As I compiled information for a presentation titled, “Industrial Hygiene in Construction”, I wondered how to approach this topic. What I decided, is that I would start with the most frequent, the most common, with the most room for improvement. So, my list begins.

The caveat is that this list is NOT a list of the relative hazard compared to each other. This is just the IH hazards I see the most frequently. They should really NOT be compared to each other.

1. Silica – in regards to airborne overexposures and lack of controls.
2. Noise – in regards to overexposures and lack of adequate controls.
3. Lead – in regards to compliance with OSHA / EPA.
4. Asbestos – in regards to training employees and compliance with OSHA/EPA
5. Welding – in regards to overexposures and lack of controls.

I have done a bunch of respirable silica dust air monitoring during drywall sanding activities. I have found varying results from the data (meaning overexposures & within the exposure limits). I have found silica in the drywall mud (or possibly the drywall itself).  I have also found that most drywall sanders wear a paper dust mask. In recent years I have not found any airborne silica in my samples. However! I have found airborne (total) dust levels higher than five times the exposure limits during sanding. What does this mean?

Well, the issue is that most drywall sanders use paper dust masks, or equivalent N95 or P100. Like this.

NIOSH has rated these masks for a protection factor of 5. Meaning that you are “allowed” to be exposed up to 5 times the exposure limit. IMO there are many things wrong with these masks. For starters, their fit on your face is really a guess. There are no “tried-and-true” methods for assuring these masks fit.*  Second, if you admit that you need to wear a respirator (meaning: you need to protect yourself) why would you choose an inferior product? I could go on…

Therefore, or finally, we come to my recommendations:

• if you’re drywall sanding:  wear a 1/2 face tight fitting respirator with HEPA cartridges. It will protect you (given a proper fit) and based on my findings, you can rest assured you won’t be overexposed.

Besides who wants to look like this at the end of the day?

*Quantitative fit testing is a reliable fit test method, but for these types of masks, I find it to be totally useless in the real-world

Asphalt milling machines are used to remove road asphalt in wide sections. It has been awhile since I’ve had the opportunity to perform air monitoring for silica on these operations. However, my experience in the past tells me that they can produce a lot of respirable silica dust. I snapped this picture while I was driving (I was going slow, but yea- probably not safe) on a road crew working.  I didn’t capture the cloud of dust hitting the sunlight, but it was a beautiful/scary sight.

The drums on the asphalt machines have many sharp teeth. The drum is lowered onto the asphalt surface and basically chews up the asphalt while carrying it to a belt. As you can imagine, the drum gets really hot. Water is kept on board the milling machine to cool the drum.  The theory is that the drum is wet, so the silica issue must be at a minimum.  I have found really high exposures to airborne respirable silica during this process. I believe due to the water NOT being directed at the cutting teeth.

The solution? Unfortunately, I don’t have an easy one. For starters, I’d make sure the water is directed at the point of cutting (which can vary from day to day). Respirator are not really an option. The road crew must communicate with each other and doing this with a respirator is extremely hard. The noise from these operations is also very high and most crews have ear muffs with communication head-sets.

I would love to hear your comments on engineering solutions to this issue. I don’t believe there is much research going into this issue.

I was at another rock crushing site this week. This company has a mobile crusher that can crush some nice sized rocks. Which, by the way, is unique, since most crushers that can handle these size rocks take various cones, belts and screens.  Air sampling conditions were definitely not “worst case” due to morning mist and cloudy conditions for almost the entire day. However, any dust that was generated was most likely from the crusher- not gravel trucks, haul trucks, or wind. We did perform airborne silica monitoring and noise dosimetry on the crushing crew.

I did emphasize some easy, but usually overlooked, tips for the crew:

• keep the doors closed! (this reduces dust and noise)
• keep the radio and CB turned down as low as you can
• backup alarms should point to the back (not at the cab)
• wear hearing protection in high noise areas (around generators)

It’s still dry here in the Northwest and the crusher operations have been in full swing. This mobile, 2 cone crusher was just moved to the coast for about a six week project. We performed airborne respirable dust monitoring and noise dosimetry on the crushing crew. We use a 37mm aluminum cyclone to obtain the respirable fraction. If you run the pump at 2.5 Liters per minute you get a balanced sample across each size in the curve -5 um (microns) and smaller. I analyze for respirable dust, crystalline quartz and cristobalite. We’ve never found trydimite in this area.

There was visible dust coming from the crusher. However exposure might be a non-issue since everyone was either in the cabs of their equipment, or in the operator’s booth.  Silica exposure is nothing to take lightly. Here is a MSHA video on the subject titled, “What Does Silica Mean to You“. (windows media)

For MSHA noise dosimetry is done very similar to the OSHA methods. There are only slight difference between the two. MSHA has a nice fact-sheet here.

You can see one of the cones in the picture below (before it was running).

I was requested to perform training for a management team (VPs, Estimators, Superintendents, PMs, PEs) on health topics. The request was specific: asbestos, lead, silica and mold/ IAQ (indoor air quality). I was given an hour, which is hardly enough time. However, the audience took well to it.  I was impressed with the questions and discussion that followed the training. Here are some highlights from that training that the management team adopted as policy. Most of these can be considered tips for good management of IH programs.

ASBESTOS:

• Before the project begins we will have (in writing) an asbestos survey
• As a contractor you typically sub the abatement work
• Employees need awareness training at some level (usually class IV)
• Any asbestos found is to be sampled (by an inspector) and NOT to be touched

LEAD:

• Before the project begins we will have (in writing) a lead survey of the building
• As a contractor we must manage lead on the project (no abatement usually)
• Any lead found on the jobsite WILL BE controlled
• Employees need awareness training – site specific
• Lead ACTIVITY (s)  must be characterized and assessed for possible exposures – and further steps

SILICA:

• There is/will be silica on our jobsite
• We WILL take steps to control the silica exposure when it occurs
• Employees will be trained as to the dangers of silica

MOLD/ IAQ:

• We will manage any mold/fungus found onsite
• We will have a plan for how we handle the situation as we arises
• We will be sensitive to any health or mold/fungus concerns

Industrial hygiene at a surface-mine rock crushing operation is primarily 2 major hazards: 1. airborne silica dust and 2. noise. (there are many more safety hazards but I will focus on IH)

Silica– this can vary due to:   the amount of silica in the rock, weather conditions, type of equipment, if water is used, and where the miners work around the crusher. If it’s a dry-day the groundmen’s silica exposure is right at the limits. Operators in enclosed booths, and loader operators are usually within the limits, unless their cab doors are open. And, as a caveat, to all of this information: you HAVE to do your own monitoring. There are just too many variables.

Noise– with only a few exceptions, noise levels (dosimetry)  are usually well above the MSHA Action limit of 85 dBA. Therefore most rock crushing operations need to have a hearing conservation program. – which for most companies is just measuring their employees hearing (audiogram) every year.  I always recommend that these companies have an active program. Rock crushers are LOUD.

MSHA inspectors, in our state, usually come out to each of the surface rock crushing sites 2x/year. I think it is great they get as many “safety” visits as they do, however, I’ve heard many complaints about the inspectors. Most complaints  stemming from silly citations that aren’t a safety issue, just a rule interpretation. But, to defend them, they have a hard job. They have to fly/drive all over the place, deal with miners, irritated owners, and make sure someone doesn’t get killed after they leave.

Mines (not just underground) can hurt people….but most people have seen that show on the news.