Almost all safety authorities require a 4:1 margin of safety below the LFL, based on worst-case conditions. This means that enough dilution air must be used to always maintain a concentration of less than 25% of the LFL, according to the National Fire Protection Association standard NFPA 86.
Experience has shown that explosions in ovens and dryers can happen very quickly. The key hazard is an explosion from the build up of solvent vapors in the oven or dryer atmosphere. This buildup could occur by a malfunction in the production process such as:
In any of these cases, the concentration of flammable vapor has an opportunity to rise above safe levels, creating a potentially explosive mixture of vapor in air.
Many industries involve coating products with a flammable solvent or mixture of solvents and then run through an oven or dryer to dry the solvents, so they are removed from the finished product.
Hazardous gases are stored and distributed in the semiconductor plant, which includes:
In these operations there exists the possibility that the hazardous gas could accidentally leak or spill into the surrounding area. Pumps, control valves, manifolds, piping junctions, fittings and connections are some of the potential sources for leaks or spills. With so many opportunities for leakage, continuous monitoring of such hazards is an essential part of keeping the plant safe.
Process tools are enclosed areas in which specific wafer processing functions occur. Any process tools handling flammable gases require a hazardous gas detection system to ensure safety and be in compliance to codes. The FM standard states that “ventilation shall be provided for all tools handling flammable and combustible liquids. Ventilation shall be provided to ensure the atmosphere does not exceed 25% of the LEL (LFL) in the event of the largest possible leak.”
Containers of hazardous gases, both flammable and toxic, are often isolated from the surrounding environment by safety enclosures (gas cabinets). Some process tools have a gas control enclosure section that serves the same purpose as a gas cabinet. It is important to monitor these enclosures for leaking gas to save product as well as prevent a toxic condition. The cabinets and enclosures are ventilated to prevent the buildup of any leaking gas.
Semiconductor manufacturing facilities employ a number of hazardous gases in their production processes.
For the past couple weeks we shined the spotlight on the Pollution Control Industry; we've looked at the three ways to reduce emissions (Oxidizers, Incineration & Solvent Recovery). This week let's discuss HOW, by looking at real life applications:
Solvent recovery systems recover and re-use solvents from manufacturing processes. Solvent laden air from the processes is passed through an activated carbon bed. When the carbon bed is nearly saturated with solvent, a steam-down cycle occurs to condense out the solvent for re-use. The carbon is then regenerated for another collection phase. Two carbon beds are used so that one bed can process the solvent-laden air while the other one is regenerating.
