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37 <br /> APPENDIX 1: <br /> Factual information concerning airborne particles <br /> 1. The most significant risk to humans from airborne solids is inhalation of very <br /> small particles, which lodge inside the lung, causing respiratory trauma and <br /> disease. These particles are roughly ten times smaller than the width of a human <br /> hair, and are literally invisible to the human eye. <br /> 2. Particles of the sizes of concern to major regulatory programs by health <br /> authorities and the EPA are PM 2.5 and PM 10. The "PM" numbers identify the <br /> rough diameter of the particles in microns, and 2.5 and 10 are used as convenient <br /> snapshots within the wider range of particulates in fugitive dust (airborne <br /> materials that escape the boundaries of a particular site or operation). A micron is <br /> one-one millionth of a meter. There are over 600 microns across the period at the <br /> end of this sentence. Many bacteria are smaller than PM 10. PM 2.5 particles can <br /> only be seen with powerful microscopes. <br /> 3. Breezes of less than ten miles per hour can pick up these and even larger particles <br /> and move them considerable distances, particularly when turbulent wind currents <br /> are encountered. For example, particles of PM 10 and smaller have been <br /> measured hundreds of miles from their point of origin. <br /> 4. Fugitive dust is primarily caused by physical processes: crushing of materials by <br /> application of mechanical force such as repeated heavy-vehicle traffic,unconfined <br /> material storage, grinding and crushing operations, and aerial entrapment of dust <br /> particles by the action of wind across an exposed surface. <br /> 5. Common sources of fugitive dust include unpaved roads, unprotected materials <br /> storage piles, transportation of unprotected materials, and heavy materials <br /> processing operations. Once fine particulate materials have left the desired <br /> containment area,they cannot be controlled. <br /> 6. Larger dust particles are gradually deposited, falling in response to gravity as <br /> "nuisance dust" closer to the source,with the smaller particles continuing to move <br /> with the wind. If the source of the dust is continuous or repeated, there will be <br /> continuous exposure to fine particles at a given location as long as the source is <br /> not mitigated. <br /> 7. PM 2.5 and PM 10 particles are so small that they respond more to wind speed <br /> and turbulence than to gravity, and hence appear in all locations downwind for <br /> considerable distances. Fog droplets (roughly PM 25), mist (PM 40), fine spray <br /> (roughly PM 60), very light rain (PM 1000, or one millimeter) and similar liquid <br /> aerosols can help us to recognize how tiny PM 10 and smaller particles really are. <br /> 5 <br />