odor thresholds

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)

Do you smell dirty clothes in your indoor building? Do you suspect your heating ventilation and air conditioning system of causing the smells?

It might be what’s called, “Dirty sock syndrome”. Typically found in high humidity locations. A brief video overview can be found here (You Tube 2:03)

Lawrence Berkeley National Laboratory has good information on indoor air quality and how it affects people as they work. They also have some scientific information about how improving the indoor space (by ventilation, temperature, particles, etc) can create a better environment.

AIHA has a “Position Statement on Mold and Dampness in the Built Environment” (March, 2013).  It lays out the reasons to control moisture in a building, and some basic steps for remedy (spoiler: air sampling doesn’t usually help).

Bottom line: Check your coils before replacing your entire system. Replacing these might be cheaper. Or, sometimes they can be cleaned, but it is a strict protocol. One possible solution is here (I do not endorsement, or recommend this particular product/brand. Do your own research).

Unfortunately I have no problem finding an appropriate picture for this blog on Ebay. People are weird. Yuk.

dirty sock

I regret I don’t have the energy to post every question and situation on this site.

However, occasionally there are very unique questions. I won’t say how I answered them, but I will offer some considerations. Here’s are my two favorites from the recent past:

  1. My construction crew is working on a “special TI (tenant improvement)”, alongside an elephant who has Turberculosis (TB). What personal protective equipment (PPE) do my workers need to wear?
    • Is the TB active
    • Does TB transfer from people to animal, and/or vice versa
    • How much contact (distance, time, amount of touching, etc) will the workers have with animal?
    • Will you offer prophylactic shots? (to the employees, of course)
  1. We are going to be excavating the carcasses of dead sheep. What type of PPE will my excavator operators need to wear while performing these tasks?
    • How large of an area (2-3 football fields)
    • How long have the carcasses been in this area
    • Any additives to the soil/area
    • Will workers be in contact with dead animals?
    • Will workers need to enter the excavation?
    • Will you use a multigas meter (4 gas)?


I’d love to hear your best (or worst) questions.

It is officially summer and construction road crews & roofing is in full swing. Some projects require the use and application of coal tar pitch. Not only is it stinky, it is is hazardous.

Here’s some info:

  • Uses
    • Roofing
    • Asphalt seal coating
    • Pharmaceutical treatment for psoriasis (scalp/skin condition)
    • Graphite industry (in the production of graphite)
  • General
    • Coal tar pitch is actually a make-up of a bunch of different substances (maybe even 10,000 of them)
    • Contains lots of polycyclic aromatic hydrocarbons (PAHs) and other chemicals including: benzene, pyrene, benzo(a)pyrene, phenanthrene, anthracene
  • Exposure
    • can be exposed by inhalation, ingestion (is this likely?), or exposure to skin, eyes
    • considered a carcinogen if the product contains more than 5% of coal tar
    • cancers include: skin, scrotal, lungs, bladder, kidney & digestive
    • increases your sensitivity to sunlight (easier to sunburn)
  • Safety
    • Pick a sealant/coating that does not contain coal tar. A list of some can be found here.
    • Avoid inhalation & skin/eye contact
    • Train your employees. A sample safety SDS (MSDS) can be found here.
    • Wear the correct PPE.
    • Air sample to determine exposures. OSHA has a method (58).
  • Resources


Let me first say that I am still learning about this hazard and why it is so dangerous.

Polyurethane foam is used as an insulating material. More info on it’s uses here. The danger is when you spray it (think: expandable type), or apply it, or cut/remove it after it’s cured. The danger is in the off-gassing.

There are two main considerations:spray foam

  • the process of applying the foam
    • spray type
    • quantity?,
    • ventilation?
  • the type (manufacturer/brand/type) of foam
    • curing rate,
    • type of hazard, etc.

What we know is that there is a hazard. AND, this hazard may not effect everyone, OR, it may not effect you until some time has gone by. But, some of the chemicals in these types of products include:

There is a huge potential for work related asthma when using these types of products. And, even contact with the skin can trigger an allergic response/asthma attack. If you have employees working around this type of product and have ANY respiratory symptoms (or asthma), please have them checked by an occupational medicine doctor.

Control of this hazard should include:

  • PPE for employees (respiratory, eye, & skin protection)
  • ventilation during application
  • ventilation during off-gassing & curing (can be 72 hours)
  • control plan for spills, cutting & demo
  • control plan for employee/occupants with asthma

The EPA has a quick reference card here (hat tip to Tom), and more detail from the EPA on how to control the hazard here. The Spray Polyurethane Foam Alliance has free training here (haven’t checked it out though), and be mindful that anyone can be an instructor (good & bad).

From what I have seen, there are not a large amount of formaldehyde exposures in construction. However, there is A LOT of formaldehyde used in construction materials. Formaldehyde can be dangerous at levels undetectable by your nose. And, the symptoms of exposure are nondescript (irritant & tingling of eyes, nose, respiratory tract).

Here are some products that may contain trace (or more) amounts of formaldehyde:

  • resins in plywood, MDF, CDX, particle board/fiber board
  • garage doors
  • drywall
  • roofing
  • glues / mastics
  • paint/coatings
  • carpets
  • insulation (spray in and batting)

I believe the reason we do not see high exposures is due to the limited duration of exposure, and the open-aired nature during the construction. Some exceptions are warehouses with large storage areas of particle board/MDF. (I have found exposures in these areas)

The OSHA exposure limit for formaldehyde is 0.75 ppm (action limit of 0.5 ppm, and short term limit of 2 ppm). However, this may not be low enough, based upon other standards (ACGIH says 0.3 ppm, NIOSH 0.1 ppm)

Another major issue with this hazard in construction is once the space is occupied.

  • Once construction is done, the space may be sealed up, heated, and additional curing can occur.
  • This may release more formaldehyde, and also NOT allow as much to escape (by dilution ventilation).
  • Compounding this issue are the type of occupants in the building. Are there children, non-working adults, immunocompromised individuals, sick, or elderly occupying this space? The OSHA standards are NOT protective for these types of people.

I do not forsee this type of sign being posted immediately after new construction.

formaldehydeOn the plus side, someone has discovered that plants may help reduce formaldehyde & VOC levels in homes. Horticulture Science Kwang Jim Kim, et.al


Many times an IH is called upon to determine the cause of a person’s ailing symptoms. For example, an employee might complain of congestion, irritability, bloody nose, etc. Someone has decided it might be from their exposure at work.homer sick

The practice of industrial hygiene is difficult to apply to an individual. What I mean is, this field of study was developed due to serious health concerns over a population of people at work. This is essentially how science works, you take a population, study it, find the differences, then make conclusions.

Trouble occurs when you try this backwards. If the same person (as example above) complains of congestion, irritability, bloody nose- can we assume they must have exposure to lead dust? Not usually. We must obtain other clues.

What industrial hygienists try to do in these instances is rule-out the possible over-exposures. Sometimes we can measure for chemical exposures to see if it might be of concern. But even then, it’s not fool proof. Below are a few issues which make it complicated.

  • exposure at work? job? extracurricular activities? home?
  • person might have autoimmune disease and gets sick easier
  • sampling is not feasible
  • sampling is somehow screwed up (by IH, lab, mail carrier)
  • exposure is through food, clothing, etc.

Even with these fallacies, there are things an individual can do to narrow down their ailments:

  • create a log. time, type of symptoms, pain scale, others experience/smell, food eaten
  • change things and see if it improves/makes it worse
  • research – but do it right. Look at the items you use, check the SDS


Many construction companies have a multi gas meter (s). Here is my word of caution: if you have one, know how to use it.

I bet if you’re reading this post, you do know how. However, do your employees?multi meter

This type of training is SO critical. Below are some common mistakes I’ve seen from construction companies using these types of equipment:

  • Let someone else (a GC, or subcontractor) tell you if it’s ok to enter a confined space (or hazardous one).
    • = do you own monitoring, & use your own equipment!
  • Use someone else’s multi gas meter.
    • =do NOT use someone’s meter unless you 1. know the machine and 2. are able to calibrate and see the documentation. Would you send your employees to work in an area you think there might be a deadly hazard? Treat the 4-gas meter like it is your only available tool.
  • Not performing a precalibration and bump test before using the gas meter.
    • = ALWAYS perform a bump test (not just zero-out)
  • Not knowing which sensors are inside the machine (and what they mean).
    • =train your employees on when/why it alarms. CO is not CO2.
  • Blame the machine if it alarms
    • =the machine is alarming for a reason. You either screwed it up, or something is going on. Figure it out. I had a project where the handheld radios were interfering with the multi gas meter. It took us 2 days to figure this out. Luckily no one was so desperate to work they ignored the alarm. On another project, employees were telling me it was ok to work while the alarm was sounding off. Their response was that, “it always goes off for CO, but we aren’t worried”. Yikes! I was.
  • Not knowing what the hazards are
    • =you must know what you are measuring for. If you have isocyanates inside the confined space, the multi gas meter is probably not going to give you adequate warning.- if any. Just like wearing the right type of filter cartridge on your respirator, know the hazard you are measuring.

There are some items you need to do BEFORE you wear a respirator. If you are using it on a voluntary basis, go here.

  1. obtain medical approvalfor employees to wear a respirator
  2. have a fit test performed
    • qualitative fit test unless you wear a full face mask, or a type better than this
    • my favorite choice is irritant smoke, but it could also be saccharine, isoamyl acetate (banana), or Bitrex (R).
  3. get trained. Learn how to:
    • clean it
    • store it
    • know what your respirator can’t protect you from
    • choose the right cartridges
    • know when you have break through
    • fit check (different than a fit test -BTW)

Wondering how often you must update the above steps? Go here. There are more steps to having a respiratory program, but you must do these things before you start.

…..: Red paint.

The point for the day is to remember that your sense of smell can be very good, or very misinformed depending on what you’re smelling (and who you are).

Sulfur (sulfur dioxide) can be smelled when it’s as low as 0.009 parts per million (ppm). The exposure limits are at 5 ppm. There are many chemicals that work just the opposite.

Before you make an assumption, figure out what you are smelling.

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