Sealing to the Osha 1910.119 process safety management standard and the clean air act of 1990. 8-10

The Process Safety Management Standard was created to prevent the unwanted releases of hazardous chemicals. The standard identifies more than 130 specific toxic and reactive chemicals covered in specific quantities and processes that involve flammable liquids and gases in quantities of 10,000 pounds or more. Hydrocarbon fuels may be excluded if used solely as a fuel.

A process is covered if it involves the toxic or reactive highly hazardous chemicals at or above the specified threshold quantity of the standard. The threshold quantity is the amount of the chemical present at any given point in time, not aggregated over a period of time. If you look in the last pages of this paper you will find a list of these highly hazardous chemicals, toxins and reactives, along with their threshold quantities.

The clean air act was created in 1990 to address the escape to atmosphere of Volatile Organic Compounds (VOC). The proposed amendments for chemical plants apply to any component in contact with a substance that is at least ten percent applicable VOC, and is in gaseous or light liquid VOC service more than 300 hour annually.

To determine the amount of VOC in a gaseous leak, the VOC is measured at a distance no more than one centimeter (less than a half inch) from the source.


Phase 1 at the onset

greater than 10000 ppm.

Phase 2 one year later .

greater than 5000 ppm.

Phase 3 two and one half years later

greater than 1000 ppm

Polymerizing polymer

greater than 5000 ppm.

Food/ Medical

greater than 2000 ppm.

All other pumps

greater than 1000 ppm.

For components with moving parts (pumps) the first attempt to repair a leak must be made within two days after the leak is detected. The standard also require the monthly visual inspection of all single mechanical seals.

Pumps with dual mechanical seals can be exempted from the monthly inspection if the barrier fluid pressure between the seals is at a higher pressure than the pump stuffing box pressure at all times and the barrier fluid is not a light liquid VHAP (Volatile hazardous air pollutant), or is equipped with one of the following three features designed to prevent VOC emissions from the outboard seal:

If a leak is detected between the seals the first attempt at repair must be no later than five days and the repair or replacement no later than 15 days.

Single seals are available that can satisfy current standards. They must be monitored monthly (EPA Method 21) and visually inspected weekly. If they are detected leaking:

The only sensible approach to the sealing of fluids and gases identified in these acts is the use of dual seals designed with a two way hydraulic balance and the barrier fluid pressurized at least one atmosphere above maximum stuffing box pressure. The tandem configuration would be a logical choice for both rotating and stationary versions of a dual seal.

In the following diagram I am showing a simple, unbalanced version of a dual tandem seal for demonstration purposes. The preferred configuration would be:

The preferred configuration should not only satisfy the regulations, but also will provide additional safety features:

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