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For the past month we shined the spotlight on process ovens & dryers; we've looked at WHAT goes on in the application, WHICH hazards to avoid and WHY they should be monitored.

Controlling flammable vapors and installing solvent vapor monitors on your process oven and dryers allows the implementation of several money-saving steps:

Moving and heating large amounts of air can be extremely expensive. Many manufacturing processes must use chemical solvents in the production of their products. As a result, hot air dryers are frequently used as a means of evaporating those solvents.

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:

• a sudden or improper amount of coating 
• a change in ventilation controls 
• excessive speed

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.

For the past few weeks we shined the spotlight on the Semiconductor Application; we've looked at WHAT happens in a facility and WHY monitoring is necessary in the different parts of the facilities (PPM,

Hazardous gases are stored and distributed in the semiconductor plant, which includes:

1. Storage Areas
2. Distribution
3. Delivery Piping

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.