Industrial Hygiene in Construction

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 measuring by air sampling for a job task, or an employee’s personal exposure, how many samples should you take?

Sometimes it is easier to place one filter cassette (or media) on the employee for the duration of their day.  At the end of the shift, you collect your equipment, mail it to the lab, and they spit out a 8-hour time weighted average (8-hour TWA). This is simple and easy to understand.

However, if you have the time and resources, it is usually beneficial to obtain multiple samples throughout the day. Taking multiple samples allow you to:

• obtain peaks, lows, and anomalies.
• look at: set up & clean up activities (separate from daily tasks)
• measure multiple employees doing the same task (to better capture the job task)
• calculate your own time weighted average
• capture short term exposure levels (STELs), or excursion limits *
• choose appropriate PPE for short duration tasks
• determine if employees are “falsifying” the data (skewing the data high or low)
• reduce filter overloading (in some cases)

There are some reasons NOT to obtain multiple samples:

• collection limit constraints (sometimes the method of sampling does not allow for this type of multiple sampling)
• it can be costly
• it is very time consuming (and nearly impossible, if you have multiple pumps on multiple employees throughout the site)
• difficulty interpreting the data (the math, the inferences, etc)

If you are hiring an industrial hygienist to perform air monitoring, ask about multiple samples. It might be slightly more expensive, but the information and data might be worth the cost.

*ACGIH recommends that if the compound does not have a STEL, all airborne levels should not exceed 3x the 8-hour TWA as an excursion limit.

Assume your general contractor reports that he has found a material (floor tile, popcorn ceiling, etc) with less than 1%. He wants you to remove it with the rest of the demolition because, as you know, “…if it’s less than 1%, it’s NOT considered asbestos containing!”.

Are you ok to remove it?

Yes, and no. There is more to consider. The “1% rule” (as it’s called) as it is called states that they only regulate asbestos containing materials if they contain more than 1% of asbestos. Here are a few other considerations:

1. OSHA definition. Don’t get stuck on the definition. If you have employees, you must still follow parts of the OSHA rules. At a minimum, you must train your employees, work practices, clean-up and disposal requirments. More details on training here.
2. How were the samples taken? If one bulk sample shows less than 1% asbestos, you still might have a problem. According to the EPA/AHERA sampling rules, some types of materials must have up to 7 samples taken. This rule is in place because, back in the day, asbestos was added to joint compound (or anything similar) and it could really vary in amount according to where you take the sample. In addition, OSHA does not allow for composite sampling (combining the layers).
3. Do you know that 0.99% asbestos is still bad for you? Asbestos is a carcinogen. The greater the exposure, the greater the risk of disease. Any exposure could be the one to cause the disease. If the material is friable and you are disturbing it, I would NOT recommend performing that activity. Hire an abatement contractor.
4. Finally.Let’s assume it’s non-friable, you are not going to disturb it (when removing it) and it’s less than 1%. What will you do if your neighbor next door decides to call OSHA/EPA? Do you have a written plan and procedure? Have your employees been trained on the hazard? How to remove it? How to dispose of it? …Sometimes bad publicity will get you in worse trouble than any monetary fine.

 

For people who work with asphalt everyday, this may be a obvious statement: Silica is in asphalt.

There are two areas where this might be of concern:

1. During the mixing of the asphalt there is usually some ratio of rocks that are added to the product. The size of these rocks is where safety personnel should have concerns. If they are adding the smallest fraction of rock to the mix, you may have airborne exposures to silica. This size of rock is called P200 (or, using a 200 sieve screen to get anything less than 200 parts per inch). Usually this is seen during the transfer of rock from the loader or from the belt conveyor.
2. The other method of exposure to silica in asphalt is if you cut it. Rocks may contain silica. When asphalt is cut, you incidentally cut through various rocks (contained within the asphalt). Silica (and dust) is released during the cutting. Please use water when you are cutting asphalt. Direct the water at the blade.

After performing an industrial hygiene survey (air monitoring), have you considered when you should resample? Here are some considerations that might help you in determining when.

• Are there specific rules that state when you must resample? For example, the construction lead standard (1926.62) states that you must resample yearly (or actually, that you can only use relevant results for one year).
• Has the process changedsince the last time you sampled? This one is hard to determine. Lot of things can change air monitoring results, here’s a “starter list” of things that can change a process.
  • Different employee?
  • Time of year? Summer versus winter? (closed up/open and humidity)
  • Is a new tool in place?
  • Has the ventilation changed?
  • Have new controls been put in place? (administrative, systems operations)
• Has the product changed? Check the safety data sheet (aka MSDS).
• Are more (or less) employees exposed to this hazard? This might change some assumptions you have made about your risk.?

If you have air sampling performed, make sure you have a written report of your findings. Laboratory results without an explanation of how they sampled, where, # of employees, process description, PPE used, safety data sheets, etc….is worthless. You may remember is well enough, but OSHA will have a hard time believing that it is a similar exposure the next time you do the “exact same thing”.

Having this report and sharing it with the employees will fulfill (part of) the hazard communication standard requirement to employees.

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:

Do you measuring dust on your project/ workplace? If you are a safety professional and you are self-performing this type of sampling here are some tips.

• Measure for the full shift (including prep and clean up) – clean up can be the worst
• Depending on the type of dust, you might need to measure by either respirable, or inhalable (IOM) methodology.  -more on this at a later date
• Watch the dust filter build-up. You might want to change the filter out so as not to overload the cassette. Especially during clean-up.
  
• Have you checked for metals? Many types of dust can contain metals. Ask the laboratory for assistance.
• Consider the placement of the sampling filter. Do you want it downwind? On the collar? Is it on the best employee for sampling?
• Do you perform an area sample? These are not usually recommended, but sometimes they can give you great information.
• Information. Capture all the information that might be important to this sampling. Time, humidity, temperature, controls (or lack of), open doors/windows, employee practices, etc.

Are you measuring for zero accidents? Is this even possible? I agree it is a worthy goal. But, if you are presenting this to management, can you actually achieve it?

There is plenty of discussion around this issue. Maybe a better goal is something harder to measure, but more successful/beneficial in the long term. What about measuring one of these? (or a combination)

• response time from complaint to resolution (from employees)
• number of requests for safety related issues
• satisfaction of safety by workers (rate 1-10)
• safety committee interest & interaction
• decrease in airborne exposure levels year over year
• keeping track of engineering/administrative controls put in place per year

My 2 cents.

Occasionally (actually, far too often), I hear from a subcontractor who was told by the General Contractor (or owner) there is no asbestos onsite. Then, after they have been working for a month they find out it actually IS asbestos, and they were disturbing it. What do you do?

The first thing to do is stop work. Do not try to clean it up. Call an abatement contractor. They will identify the asbestos onsite, clean it up, and provide an airborne clearance test.

Next, you will need to provide awareness training (or better, let the abatement company provide it). Ideally this will occur on the day you start back working. Train everyone onsite about asbestos.

Finally, you (as the safety manager), need to identify and characterize the exposure to the employees. It should probably be a formal letter written to the owner, general contractor and employees.

Here are some tips on writing the letter:

• include employee names, work hours, type of work, PPE worn, and locations they were working
• describe the asbestos. Amount found, locations, type, estimated amount disturbed.
• describe remedy process and steps taken. Names of GC, owner, abatement company, airborne levels found. Who was trained afterwards.
• describe how things will change in the future. Here’s a tip:  any building before 1985 WILL have a building survey performed for asbestos….in writing.

Really, one exposure to asbestos is probably* not enough to contract a disease (asbestosis, or mesothelioma). It will take 15-30 years for symptoms to appear. But, it might be worth the “goodwill” to send affected employees into a occupational health doctor for a check up. The physician will reassure the employee and may provide some comfort.

*asbestos is a carcinogen. Greater exposure = greater chance of cancer. no amount is safe.

Living in the NW, stucco is not as prevalent, compared to other areas of the US, as a building material. I finally got the opportunity to perform air monitoring for silica during stucco crack repair. From what the contractor explained, only the top layer of stucco (1/8 inch) is removed. He claimed the top layer is mostly an acrylic. The employee was wearing a 1/2 face tight fitting respirator with P100 (HEPA) cartridges. In addition, engineering controls were used.  The contractor had a grinder with a shroud and vacuum to remove the dust. This would not be considered a worse-case sampling scenario. From conversations with the plasterer-employees onsite, grinding is usually “VERY dusty”.

Sampling performed only for the duration of the grinding (3 hours). Conclusion?: We did not find any detectable levels of silica or respirable dust.

Please don’t use this sampling as the only information on how to proceed for your project. However, here are my observations:

• If acrylic material is the top 1/4 inch, you may not impact silica (or have any airborne).
• Airborne dust was very well controlled by grinder with shroud & vacuum (see pic below).
• Assume you will have dust until you can observe (or prove) otherwise. Wear a respirator.
• Perception is huge. If there is a big dust cloud coming from your grinder—even if there’s no silica… the observers don’t know the difference, and, well,…you know the story.