In a message dated 11/16/05 2:53:47 PM, Viateur writes: <<What are the health problems that might result from the use of dry perlite ?>>
Perlite is primarily silicon, volcanic in origin & 'puffed' by rapid heating. The resulting material is then crushed into the desired size (a more scientific definition may be found at the end of this post). The perlite typically found in garden stores is processed further & has much less dust - but is too small to be useful in most orchid culture. 'Sponge rock' is only partially refined & includes a large amount of silicon dust. It may not feel like you're rubbing glass shards between your fingers, but that's essentially what happens when you breathe it in. The dust is difficult to remove once it gets into the lungs and results in scarring called silicosis. In coal miners, it's called Black Lung. Wear a mask & goggles (preferably a respirator) when handling dry perlite or dry mix containing perlite. Rinse your perlite before use - the dust just clogs up the air spaces you're trying to create. Damp your media before potting. It doesn't have to be wet - just enough to keep down the dust. I make up batches of media in a concrete mixer. The sponge rock & charcoal is rinsed in a 5-gallon bucket with holes drilled into the bottom. That goes into the mixer first - otherwise it stays at the top & doesn't mix well. Bark, coconut husk, etc. is soaked & drained a week before to give it time to drain well. Ammendments like lime go in last. Any mix I don't use that day gets spread on a tarp to dry down some, then stored in a large open bin. For gardeners/orchidists, another common source of silicon dust is diatomaceous earth which is made up of the 'shells' of diatoms (single-celled aquatic organisms). Use a mask when spreading this around or refilling your pool filter. "Perlite is a light gray, glassy volcanic rock with a vitreous, pearly luster and a characteristic concentric or perlitic fracture. It differs from other volcanic glasses principally in its combined water content, which produces the unusual characteristic of expanding up to 20 times its original volume upon being exposed to rapid, controlled heating. The resulting expanded particles are spherical in shape, usually fluffy or frothy, highly porous due to a foam-like cellular internal structure, and have a very low density." _______________________________________________ the OrchidGuide Digest (OGD) orchids@orchidguide.com http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
