The "mental dusts" are referring to the Eight Mental Dusts. Breathing NORM contaminates from dusts should be prevented by wearing respirators with particulate filters. Sodium fluoride is classed as toxic by both inhalation (of dusts or aerosols) and ingestion. Flammable dusts when suspended in air can explode. The respirable fraction of lunar dusts may be toxic to humans. The short-term exposure limit is set at 3 mg/m for caprolactam dusts and vapors. Control involves application of insecticides in various forms including dusts and liquids. An additional route of exposure is inhalation of atmospheric gases and dusts. Examples of low-resistivity dusts are unburned carbon in fly ash and carbon black. Some coal flue dusts contain small quantities of gallium, typically less than 1% by weight. Occupational exposure limits exist in many countries recognizing the hazard of wood dusts. Some exporters focus primarily on broken-leaf teas, fannings, and dusts. After the whole-leaf teas, the scale degrades to broken leaves, fannings, then dusts. Whole-leaf teas are the highest quality, followed by broken leaves, fannings, and dusts. It is a component of dusts from blast furnace refining of lead.