This hazard is somewhat difficult to understand. There are number of reasons for the confusion, but the easiest way to explain it is to realize that:


Diesel exhaust = Diesel particulate matter (DPM) = lots of different chemicals & particulates

AND: There is not a perfect way to measure the exact exposure.

The Long Story:

The term ‘diesel particulates‘ includes the following (not a comprehensive list):

  • elemental carbon (the most reliable method for testing occupational exposure to exhaust, Birch & Cary 1996)
  • organic carbon
  • carbon monoxide (CO)
  • carbon dioxide (CO2)
  • hydrocarbons (PAH)
  • formaldehyde
  • oxides of sulfur & nitrogen

You can quickly see that these are very different substances, and to make it more confusing, you can change the amounts by:

  • the fuel (on road/off, low emission fuel, biodiesel)
  • the motor type
  • the tuning of the motor (& dynamic versus idle), new motor restrictions
  • scrubbers, etc.

In addition, there are not any well-established occupational exposure limits specifically for diesel exhaust. However, the International Agency for Research on Cancer has classified “whole diesel engine exhaust” as a carcinogen (cancer causing), so there is reason for concern. Most of the research and rules are in the mining industry, which uses a lot of diesel equipment and the exhaust really has no where to go.

  • OSHA = none, but they have a hazard bulletin, and of course, some of the components have exposure limits
  • MSHA = 0.4 mg/m3 for total hydrocarbons and 0.3 mg/m3 for elemental carbon
  • Canada (CANMET) for respirable combustible dust (66% of respirable dust in mines is from diesel exhaust) = 1.5 mg/m3
  • ACGIH = none (for now)
    • 1995 proposed 0.15 mg/m3 (for diesel particulate matter)
    • 1996 proposed lowering it to 0.05 mg/m3 (for diesel particulate matter)
    • 2001 proposed a different limit of 0.02 mg/m3,
      • but for elemental carbon and
      • said it was a suspected carcinogen
    • 2003 withdrew proposed limit- citing not enough scientific information

Bottom line:

  • control the exhaust & where it goes (better fuel, better mechanical, scrubbers, ventilation).
  • most exposures to diesel are below the (now retracted) ACGIH TLV of 0.02 mg/m3 (or 20 ug/m3) (Seshagiri & Burton, 2003).
  • If you have a confined area, unusual concerns, or a particularly stinky situation; measure for multiple parameters (CO, CO2, elemental carbon and maybe NOx, and SOx). Compare these to their respective limits and classify the exposure (describe the conditions)

As I have said in an earlier post, some OSHA, EPA, and MSHA rules are a good fit. They blend well with health research, scientific technology, good practices, and a low-cost-of-compliance for employers. Other rules are just bad. They are  totally out of date, not protective enough, or just not feasible/practical. Here’s my plug for a good safety manager/industrial hygienist – A good one will know which rules/guidelines to follow.

The New York Times (July 19, 2012, Cara Buckley) recently wrote an article on the US noise standards which are not protective enough for employees. In construction we also have three additional problems.

  1. hearing loss is expected (or at least assumed in certain fields – carpenters, sheetmetal, ironworkers, etc.) and,
  2. work shifts are usually over 8-hours. Noise exposure is usually calculated on an 8-hour time weighted average. During the busy months, an 8-hour work day is rare. It’s at least 10, maybe 12-14 hours. This doesn’t allow your ears to “rest” between shifts. For more information on extended work shifts go here.
  3. extracurricular activities contribute to overall hearing loss – my point is that most construction workers don’t sit at home at the end of their shift. Almost everyone I know in construction is involved in one of these activities: hunting, shooting, motorcycles, water sports, yard work, cars, wood working/cutting, concerts, music, etc. Each of these activities contribute to their overall hearing loss, and again, doesn’t allow your ears to “rest”.

…which reminds me that I need to keep a set of ear plugs in my motorcycle jacket.

Here in the Northwest, rock crushing definately has a season…and that season is now. Road crews are getting set up and now is the time to make sure you get everything is in order…before the MSHA inspector shows up.

Below is my safety punch-list, specific to industrial hygiene:

  • Training – I know it’s required for MSHA sites, but double check. Does everyone have it? What about contractors onsite?
  • Water controls working & in place? The dust isn’t bad, yet.
  • Air monitoring for silica – done it yet? Are you at a new location? New part of the quarry? Better do it again.
  • Miner’s hearing checked (audiogram taken?). Anyone with a threshold shift? Make sure you follow up with another test.
  • Are the air conditioning units working in the vehicles? – if they’re not= the windows will be down = noise levels WILL be up.
  • Noise monitoring (dosimetry) performed 8-hour time weighted averages? If you don’t do it, MSHA will (maybe will be citation too).
  • Is your shop done hardfacing the equipment? see my earlier post here.
  • Paperwork in order?

Be safe out there!


Sometimes when I am at an employer’s site I am amazed at how hard people work and the determination and skills they muster to complete the task at hand. Other times, I realize how hard their job is on their body, health and being. Since I am in the U.S., I rarely get to see “horrific” conditions, but I know they exist.

Pictures are such a great to describe working conditions. If you have time, look at the pictures by on coal mining around the world. For me, it is a reminder of how blessed we are to live where we do.

This question, at times, can really make a difference with how you proceed. Where you get your information, and, more importantly, who provides the information is essential. Not only for compliance, but also for how your employees are protected.

Unfortunately, the answer is often complicated.

To address this question, the answer is YES. They all might overlap depending on what you are doing, and in what situation. I will attempt to briefly summarize when each specific rule or standard might apply.

  • OSHA – if you have employees and they work for you – you must comply. Sometimes each state (Washington, California, Oregon all have their own) may have a specific rule that enforces a bit differently, but Federal OSHA is the minimum rule.
  • MSHA – if you are operating in a mine (surface or underground) they have jurisdiction. Your shop may (or may not) be in their umbrella.
  • ACGIH – If they are referenced, it is usually a good practice to follow their rules. Look specifically at the date of the information. ACGIH updates their information yearly and is protective of the employee. Follow these rules if at all possible.
  • AIHA – Another good recommended source of information (like ACGIH). However, they just announce they will not be updating (due to funding) their WEELs and BEELs.
  • State rules – Occasionally, or more likely, depending on the specific issue, states will make specific rules. The Department of Human Services or similar will provide protective rules for the public. This may be an issue if your are working on a public project, or where small children, HUD, or other specific situations arise.
  • Local rules – Similar to the state rules, sometimes a city will make rules to protect it’s citizens. Being active in the local community is the easiest way to find these rules. Searching through the local city or county rules is a chore, but may reveal some obscure rules.

Finally, at more importantly, why are we looking at rules?

I would suggest focusing on employee health, employee concerns, best practices, and available data to best help our employees. They perform their jobs for a long duration in the day. They usually have the answer, or the best suggestion for fixing it…if we would listen.

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.

Some people really know how to stir it up, don’t they?

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).

Whom enforces the rules?

Based upon my previous post, and my reference to  MSHA (Mine Safety & Health Administration),  I realized I should back up a bit and explain why MSHA matters. The differences of who is regulating the site is subtle, confusing, and terribly important. Given the right cirumstances, all 3 could be at one location with a different boundary-line. And there are others too…

  • MSHA– Mine Safety & Health Administration.   It is clear that if you are working in a shaft mine, they are the ones who regulate you. However, the not-clear part is if you own a rock crusher and occasionally decide to crush some rock. MSHA jurisdiction if you sell the rock. If you crush it onsite, and leave it for your own use, then it might be OSHA. In Oregon, most of the MSHA activity is through metal/non-metal surface mines.
  • Federal OSHA – Occupational Safety & Heath Administration. Governs anyone who is an employee (who has employees)  So what do they do? They enforce, help, govern, provide assistance for employees. In some states, Federal OSHA doesn’t control your state because many states have their own state-run OSHA which does these tasks. Some states without a state-run OSHA are: Idaho, Colorado, Texas.  Federal OSHA classifies the ares into regions. (Idaho is region 10) I’m not an attorney, but I’ve heard that if you are an owner (or in some cases there can be multiple owners) and are not paid hourly, and don’t have any employees, OSHA does NOT have jurisdiction.
  • State OSHA – (aka Oregon-OSHA, L&I (Labor & Industries -Washington), CAL/OSHA (California), Arizona (Industrial Commission of Arizona) These states (and others) have their own state-run OSHA program. The states are required to adopt the Federal OSHA regulations so they can be “at least as effective as” Federal OSHA. Some states have more-stringent rules. This is fine as long as it is as-protective-as the Federal rules.  An interesting fact is that in Oregon there are tribal Indian lands. Even though we have a state-run program, Federal OSHA has jurisdiction if you are working on that land. Another example of this is railroads.
  • Others – Now, there may be other rules and regulations depending on where you are working and what substances you are handling. There is the Department of Transportation (DOT). City rules, Housing and Urban Development (HUD).
  • Other-Others – To make it more-confusing, these are just the “rules”. There are many, and I would argue, better, resources for the most-protective guidance in employee health & safety. Some of these examples are: American Conference of Governmental Industrial Hygienists (ACGIH), American National Standards Institute (ANSI), and National Institute of Occupational Safety & Heath (NIOSH), among others.

My opinion is the rules should be secondary to this:  Are your employees safe? If we are protecting them, the rules are only a start.

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