Granular Airborne Risks

March 2015

FD-85 (Floor Dry) is a dried, granular diatomaceous earth product. The ore from which FD-85 is manufactured, is composed primarily of the frustules of diatoms (amorphous, opaline silica – SiO2.nH2O), with minor quantities of associated detrital and precipitated minerals. These associated minerals include various feldspars, clays, limonite, and quartz.

The drying process drives off all free moisture, a portion of the water of hydration, and also promotes oxidation of some of the trace minerals. The drying temperature and duration are not high and long enough to result in a change of phase in the diatomaceous silica from amorphous to crystalline.

Therefore, FD-85 and similar granular DE products from EP Minerals (including MP-77, MP-79, Axis, etc), only contain small quantities (< 1%) of crystalline silica that are naturally found in the diatomaceous ores. The crystalline silica phases that can be present are quartz and occasionally minor amounts of Opal-C or cristobalite (a phase of crystalline silica that is associated with volcanism and often forms in flux-calcined diatomaceous earth products). FD-85 typically has the following chemical makeup:

SiO2 (amorphous)

88.4 %

SiO2 (quartz)

0.3 %


5.9 %


2.3 %


0.6 %


0.5 %


0.3 %


0.4 %


0.4 %

Other Oxides

0.4 %

Loss on Ignition

0.5 %

In comparison to clay-based sorbents and typical soils, FD-85 typically contains much less crystalline silica. Clay-based sorbents usually contain 3 to 10% crystalline silica (quartz), while common soils can contain well over 10% quartz.

The Permissible Exposure Limit (PEL) is defined as the time weighted average maximum amount to which workers can be exposed for an 8 hour shift during a 40 hour week. Under OSHA regulations, DE is included under Table Z-I- A, Limits for Air Contaminants, Federal Register, Vol. 54, No. 12, effective March 1, 1989, which is presented in the following table.








Quartz (respirable)


Cristobalite: (respirable)


Tridymite: (respirable)



Diatomaceous Earth, containing


less than 1 % crystalline silica


Inert or Nuisance Dust:


Respirable fraction


Total dust


The crystalline silica concentrations for the application of these limits are to be determined from the fraction passing a size-selector with the characteristics given in 29 CFR 1910.1000.

The granular nature of the Floor Dry and similar products means that the quantity of respirable dust in the product is extremely low. At the manufacturing facilities at which our granular DE products are made, our industrial hygiene program has consistently demonstrated that airborne levels of crystalline silica-bearing dusts are well below the permissible exposure level. In fact, crystalline silica is rarely even detected in the dust samples. When airborne levels are below PELs, respiratory protection is not required.

The use of these products can require the pouring of the product from the bag, and smaller particulates can become entrained in the air during this activity. The relative danger of inhalation exposure to crystalline silica in this case is extremely low, and use of dust respirators is not normally required. If such protection is desired, we recommend the use of dust masks rated to N95 specifications.

Peter Lenz,
Senior Research Scientist EP Minerals, LLC