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Fly Ash Exposure Concerns

Fly ash is the residue from the combustion of coal. Depending upon the source of the coal being burned, the components of the fly ash produced vary considerably but all include substantial amounts of silica (silicon dioxide, SiO2) both amorphous and crystalline (~18-70%) and lime (calcium oxide, CaO 1-30%) which are the major components of exposure concern. Understanding these concerns will help communities make informed decisions concerning the transport and use of this material in their midst.

In and of itself, fly ash is neither toxic or poisonous, nor is it considered hazardous EXCEPT when it becomes airborne! When released into the atmosphere, fly ash can be extremely dangerous to humans as well as all other animals.

To understand how and why this happens we need to “look” at these particles, particularly “crystalline silica” and the calcium oxide. Common “blow sand” with which we are all familiar, is made of “amorphous silica” which, if you could see one particle of it would look a little like a potato, rounded, smoothed and uneven. So, when you breathe a bit of it, it does not cut or scar the lungs. However, “crystalline silica” has a regular, repeating shape that is very sharp and pointed if you could see a part of the crystal. As an example, quartz crystals are composed of silicon dioxide and they are extremely hard, just behind diamond and corundum in hardness! So, when you breathe in “crystalline silica” it will cut the air sacs in your lungs forming scar tissue which reduces lung capacity. How small must something be before it is respirable? At 7 microns, particles can be breathed into the lungs. To put this into perspective, one micron is one one-thousandth of a millimeter which you can imagine if you could cut a pencil point into one thousand slices! One of the slices is a micron. About 20-40% of fly ash is in this 7 micron range including all of the crystalline silica. Now, how much of this must there be present to be considered unsafe? Sorry, but more numbers are required to make this understandable! OSHA and EPA list allowable crystalline silica in the atmosphere as 0.10 mg/m3. This is one tenth of one one-thousandth of a gram of crystalline silica in one cubic meter of air! Again, to “see” this imagine a normal raisin that weighs about one gram. Cut it into 1,000 pieces! Now, cut each of those pieces into ten more pieces. This gives you ten thousand pieces each of which is the stated 0.10 mg listed in the regulation. It takes the weight of just ONE of these raison pieces when it’s crystalline silica in a cubic meter to reach the allowed amount. Could you see the silica dust created by this amount? Of course not! So, you can’t know when the danger exists. If you could see the fly ash dust you are in severe danger as this is over 50 times the allowed limit!

What are the consequences of breathing this silica dust? As mentioned, it will cut and scar the delicate tissue of the lungs which could lead to bronchitis, silicosis and lung cancer. How long would this take? Allowable limits are based upon healthy adults, for the most part, where 5-20 years are required. But, children, asthmatics of any age, allergy sufferers and the elderly all of whom have reduced lung capacity can be affected in shorter periods of time. Further, exposure to silica dust is not limited to the lungs. It is irritating to the skin causing contact dermatitis by abrasion. Similarly, silica exposure causes eye irritation resulting in tearing and redness.

Now, as if that were not enough, lets look at the effects of contact to the other fly ash ingredient of concern, lime which is calcium oxide, CaO. This chemical reacts with water, H2O to form calcium hydroxide Ca(OH)2 which is a base. This causes fly ash to be very alkaline in nature with a pH somewhere between 10-12, a medium to strong base. What does this mean? When you breathe in calcium oxide (its dust is well under 7 microns) it combines with the water in your air passages and lungs causing a burning sensation as it can dissolve the sensitive tissues in these regions. Remember Draino? It is simply a strong base used to dissolve grease, fats, hair, etc.! Calcium oxide has the same effect upon your eyes and skin causing burning and irritation.

Again, the same groups listed above, children, asthmatics, allergy sufferers and the elderly are most at risk.

In summary, fly ash is not your normal dust. When it is airborne, it is a significant health hazard to those that become exposed. OSHA lists safety glasses with side shields, respirators with standards level marked, gloves as well as clothing that covers all skin for workers in an airborne fly ash environment. Communities can not provide this for its residents. Therefore, if a community decides to include fly ash based industries in its economic plan, then community leadership can require that fly ash bulk pumping operations be accomplished with closed pumping systems and that storage and handling have approved automated spill containment equipment. In the event of a major release of fly ash into the atmosphere, warning equipment for alerting all affected residents must be in place.

Peter Gillespie, Ph.D.
May 17, 2003