 The warmth of natural slate creates a permanent image of unrivaled quality and style. Today's leading architects, designers and building professionals prefer the rugged beauty of slate for a wide array of applications. The purpose of this video is to illustrate the best industrial hygiene practices in order to reduce hazardous exposures to both noise and dust during milling. Slate is a micro granular metamorphic rock and is characterized by excellent parallel cleavage. It is this cleavage that permits the rock to be easily split into slabs or shingles which depending upon the quality and size will determine its usage. The majority of the slate mined in this country is used for roofing. In recent years there has been an increased demand for slate shingles due to their decorative, durable and noncombustible properties. One of the minerals found in slate is quartz or crystalline silica. Silica dust presents a health hazard in many mining and milling operations. Dust and slate milling operations can contain between 15 and 40% silica. Respirable silica dust is very small in size and not visible to the naked eye. Because silica dust is small, it can be breathed deep into the lungs. Once in the lungs, the silica scars the lung tissue and restricts breathing. This scarring is called silicosis. The diagnosis of silicosis may be accomplished by obtaining a complete occupational history, chest x-rays and lung function testing. These x-rays should be evaluated by a qualified medical professional called a bee reader who is experienced in reading for silicosis to detect the disease in its early stages. Lung function tests should also be conducted every year by a qualified technician or physician. These tests will help track any changes in the worker's ability to breathe. Silicosis is an incurable disease, but can be prevented by controlling workers' exposure to silica dust. Another health hazard associated with slate mining and milling is noise exposure. Noise is generated from the rotary motion of saws and drills or the impact from splitting or trimming slate tiles. Prolonged exposure to these noise sources can result in varying degrees of hearing loss, depending on the magnitude of the noise and the duration of exposure time. The production of roofing slate requires close interaction between miners and the rock itself. This interaction exposes the employees not only to high concentrations of silica dust, but also to excessive noise levels associated with cutting, splitting, and trimming of the rock. The effective control of noise and respirable silica-bearing dust in the slate industry has long been a major concern of the Mine Safety and Health Administration, MSHA. Representatives of MSHA's Technical Support Center have visited a number of slate operations in the metal and non-metal northeastern district in order to assist the district and the mine operators in solving these difficult health-compliance problems. The production of roofing slate starts in the quarry. Occasionally, an air hammer, or in some cases, steel wedges and a sledge hammer are used to reduce thick slabs of slate to smaller size prior to entering the mill. In the mill, the slabs are placed on a metal conveyor table and transported to a diamond-edged saw. The first saw is referred to as a strip saw. It is used to cut off the rough edges of the slab, which are manually discarded. The squared off section of the slate is then cut into various width strips. After the stone has been cut into strips, it proceeds along the conveyor to the second diamond-edged saw, which is referred to as the block saw. The operator rotates the strips of slate manually with a pry bar or with the assistance of a positioning piston and cuts them into rectangular blocks. Dust control for both types of sawing operation is the same. The saw is the main dust source in a slate mill. If dust from the saw is not controlled, the entire mill will become contaminated with dust. The saw room should be separated by walls from other parts of the mill. The slate should enter and exit the room through strip curtains. Water applied to the saw acts to cool the blade while it traps dust particles and carries the dust away from the slate. Wall-mounted exhaust fans or localized exhaust ventilation should be used to create a negative pressure in the enclosure to carry away the dust. Typical airflow in the saw room is 3,000 cubic feet per minute or 3,000 CFM per saw. This airflow can be reduced by reducing the volume of the saw room. The air exchange rate should be 10 air changes per hour. For a 10 by 10 by 10 saw room, the airflow would be 750 CFM. The airflow for the mill should also provide 10 air changes per room. A 50 by 100 by 10 foot building would have to have an airflow of 8,500 cubic feet per minute to achieve 10 air changes per hour. A chimney located behind the saw allows entrained dust and dust-laden water vapor to be directed out of the saw room. Once the slate is cut into blocks, it is transported out of the saw room to the splitting line or stations. The splitter positions the block and then with a hammer and chisel, cleaves them into the desired thickness. To the extent practical, water should be used to wet down and wash off any accumulated dust from the sides of the slate blocks or shingles before they are split or trimmed. A localized exhaust system should be used to capture the dust that is generated during the actual splitting process. The closer the exhaust fan is to the point where the dust is generated, the better it will be able to capture and carry away the dust. If a wall-mounted fan is utilized, the splitter's position should be located as close to the fan as possible. Typical splitter fan volume is 1,000 CFM for each station. Once the splitter cleaves the block into the desired thickness, the slate tile is then trimmed to the desired width and length. This is accomplished by inserting each shingle into a dresser. The dresser has an electrically powered rotating blade inside of a close fitting box. The dresser or trimmer is placed against an outside wall and an exhausting wall fan is within the dresser enclosure. Dust generated from within the enclosure is typically exhausted either outside of the mill building or, more preferably, into a filtered dust collector. In order to be effective, both the enclosure and exhaust system must be properly designed and maintained. The velocity of the exhaust air should be fast enough to keep the dust particles in suspension. Generally, an airflow of at least 500 CFM is needed for each trimming station. Mounting holes are either drilled or punched into the shingles. Dust from hole drilling should be controlled by localized exhaust ventilation. The duct inlet should be placed behind the drill. The airflow at the drill should be 500 CFM. The finished shingles are stored on a pallet and, when full, the pallet is transported to a storage area. Additionally, good housekeeping should be practiced routine by washing down the floors and work surfaces to remove any accumulation of dust and prevent it from becoming airborne. Workers should be trained in the hazards of respirable silica dust. In order to assess the effectiveness of dust controls, the workers' exposure should be monitored annually or whenever there is a change to any of the controls. This monitoring is accomplished by the worker wearing a sampling unit for the entire shift. The dust sampling assembly consists of a filter, cyclone and dust pump. After the sample is collected, the cassette is analyzed in a laboratory for dust and quartz. Significant noise exposures have been measured throughout all phases of the milling operation. However, the highest noise levels are those generated by the strip and block saws. Slade operators have addressed this problem in differing manners. One such example was the construction of a permanent wall with access doors to the saw. This, coupled with the use of positioning piston between the rollers and girdling calipers to hold the stone, is very effective in protecting the operator. Another example is by building an enclosure around the saw itself. In order to increase the effectiveness of this design, strip curtain material was cut and affixed to the sides of the enclosure. This configuration not only blocked the noise and dust from the operator, but it permitted the free flow of stone as it passed the saw blade. In order to evaluate another type of control, a joint cooperative noise control demonstration was conducted between a Vermont slate mill and the physical and toxic agents division of MSHA's Brewston Technical Support Center. The concept was to construct a viable enclosure around the operator. Construction began by building a supporting framework around the saw controls. The overall design was to form the enclosure with two L-shaped doors, each with two windows. The inside of the enclosure was treated with a quilted fiberglass blanket material to absorb what sound passed through or leaked into the enclosure. On-site measurements showed a reduction of 19 DBA, from 107 DBA outside the enclosure to 88 DBA inside the enclosure. In order to accurately quantify the overall noise reduction, scientific quality tape recordings were made. These recordings were analyzed at MSHA's Brewston Health and Safety Technology Center. The original tape recorded noise is run through a one-third octave frequency analyzer, which takes the sample and displays it in frequencies from 25 Hz to 10,000 Hz. This information is then used to determine the effectiveness of engineering noise control. It is evident that this type of enclosure is not only viable from a production standpoint, but that it provides the necessary protection from the noise generated by sawing slate. The implementation and maintenance of these controls will afford permanent and adequate health protection to the employees in the slate industry.