Viskase Corporation - Executive Summary

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Viskase Corporation is a manufacturing facility that produces cellulose food casings for the meat packing industry.  Viskase utilizes the regulated chemical carbon disulfide in the cellulose food casing process.  Viskase's commitment to providing a safe, healthy work environment for employees as well as providing a safe, healthy environment for the surrounding community is supported by Viskase's installation of  the latest technology in process controls, active mitigation, passive mitigation, and monitoring detection systems.  Viskase adheres to all applicable Federal, State and local safety and environmental regulations for the prevention of releases of this chemical. 
A worst-case scenario analysis was conducted for the carbon disulfide process at Viskase utilizing requirements containe 
d in EPA guidelines.  EPA has defined a worst-case release as, "a release of the largest quantity of a regulated substance from a vessel or process line failure that results in the greatest distance to a specified endpoint."  The release is assumed to occur instantaneously.  Administrative controls that limit the quantity of a substance in a vessel or pipe can be considered when determining the worst-case scenario.  The possible causes of the release or the probability that such a release might occur is not considered in the worst-case scenario analysis; the release is simply assumed to take place.   
For toxic liquids, such as carbon disulfide, the total quantity in a vessel is assumed to spill onto a flat, non-absorbing surface.  Only passive mitigation systems may be taken into account for the worst-case consequence analysis.  The total quantity spilled is assumed to spread instantaneously to a depth of 0.39-inch (1 centimeter) in an undiked area or the spill will cover a diked area 
instantaneously.  The release rate to air is estimated as the rate of evaporation from the liquid pool. 
The toxic endpoint for carbon disulfide is 0.16 mg/L.  This airborne concentration has been published by the American Industrial Hygiene Association (AIHA) and is the maximum airborne concentration below which is believed that nearly all individuals can be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action. 
Meteorological conditions for the worst-case scenario are defined by EPA Guidance as atmospheric stability class F (stable atmosphere), wind speed of 1.5 meters per second (3.4 miles per hour), and ambient air temperature of 25 degrees C. Topography for the worst-case scenario is either rural or urban. 
The analysis conducted by Viskase Corporation identified the worst-case carbon dis 
ulfide release as the carbon disulfide railcar splitting open while spotted on site. Due to the conditions required by EPA, it is assumed that the entire contents of the railcar will release instantaneously.  Containment walls or "splash walls" are located around the railcar, with the exception at the ends of the railcar, that direct any release or spill into the containment that is located directly under the railcar.  The ends of the railcar are protected by splash baffles in the containment basin.  The containment, which contains four (4) inches of water, will hold the entire contents of the railcar. 
Viskase calculated that 99% of the total volume released from the railcar would flow into the containment beneath the railcar.  One percent (1%) is assumed to "splash" onto the ground surrounding the railcar due to the wave action if the railcar were to rupture instantaneously.  The total amount that could be released from the railcar is 105,100 pounds.  Therefore, one percent (1%) of  
the release would be 13.53 ft3.  A spill of carbon disulfide from the railcar would: 1) flow into the containment underneath the railcar, and 2) splash from the containment area onto the ground around the railcar.  Carbon disulfide is heavier than water, therefore, the carbon disulfide that flows into the containment would sink beneath the water level which would act as blanket and will eliminate the carbon disulfide from evaporating to the air.  Therefore, only the surface area of the amount "splashed" as a result of the release (13.53 ft3) is used to calculate the evaporation rate and the duration of the release.  The distance to the toxic endpoint of the release is based upon the evaporation rate and duration of the release from the amount that splashed. 
A wind speed of 1.5 meters per second and an atmospheric stability class of F was used in calculating the worst-case scenario per Risk Management Guidance, and the topography of the area surrounding the property is urban.  
Using t 
hese parameters it was determined (using EPA Offsite Consequence Analysis Guidance tables) that with a carbon disulfide release of 13.53 ft3, an estimated distance to the toxic endpoint of 0.16 mg/L is 0.87 miles. 
This worst-case scenario does not take into account Viskase's active mitigation measures that are in place for the carbon disulfide system, and or materials of construction of the railcar, that would make a release of this type improbable.  The railcar unloading location is equipped with a deluge system that is triggered manually or by heat sensors that will protect against vapor ignition.  In addition, Viskase's operating procedures require constant monitoring of the railcar during unloading activities, which improves emergency response time.  
EPA requires that an alternative scenario be analyzed for each regulated toxic chemical present above the threshold quantities. The release scenario must include consideration of the following: 
1. Tran 
sfer hose releases due to splits or sudden uncoupling; 
2. Process piping releases from failures at flanges, joints, welds, valves and   
  valve seals, and drains or bleeds; 
3. Process vessel or pump releases due to cracks, seal failure, drain bleed, or 
  plug failure; 
4. Vessel overfilling and spill, or overpressurization and venting through 
  relief valves or rupture disks; and 
5. Shipping container mishandling and breakage or puncturing leading to a spill. 
Alternative release scenarios, as required by EPA guidance, should be those that lead to concentrations above the toxic endpoint beyond the facilities fence line, unless no such scenario exists.  In identifying alternative scenarios, active mitigation systems are allowed to be considered, such as interlocks, shutdown systems, pressure relief devices, flares, emergency isolation systems, and fire water and deluge systems, as well as passive mitigation systems. 
Meteorological conditions for the alternative release scenario are d 
efined by EPA Guidance as atmospheric stability class D, wind speed of 3.0 meters per second, and ambient air temperature of 25 degrees C and 50 percent humidity.  Topography for the alternative release scenario is either rural or urban. 
The alternative release scenario identified for the carbon disulfide process would be a release due to a leak or break at a flange on the pump side of the piping.  This scenario was chosen because a release of this type is the only alternative scenario identified that would lead to concentrations above the toxic endpoint beyond the facilities fence line. 
If a break or release at the flange at this location occurred, the amount being pumped from the pump plus the amount from the piping from the pump to the nearest backflow valve would represent the total quantity that could be released.  The backflow valve located on the piping would prevent any carbon disulfide from  flowing back in 
to the piping from that point on.  The amount of piping, which is two inch (2") Schedule 10 stainless steel, from the backflow valve to the break or site of the release is approximately 500 feet.  The carbon disulfide (CS2) process pump is equipped with CS2 sensors, which detect CS2 in the exhaust gas at the pump.  When this sensor is triggered, an audible alarm is sounded.  Viskase carbon disulfide operators can manually stop the pump from the control panel; but if operators fail to manually shut the pump off, the pump automatically stops operating after two minutes even during normal operations.  Therefore, in the event of a leak or break at the flange in the piping at the beginning of the pump cycle, the pump would continue to operate for 2 minutes.  Therefore, the total amount of CS2 that would be released is the amount released from the pump operating for 2 minutes and the amount released from the piping from the backflow valve to the break.  A release of carbon disulfide at this  
area would flow onto a concrete pad beneath the flange, which then directs the flow of carbon disulfide into the railcar containment area.  Fifty percent (50%) or more of the total release would flow into the containment basin underneath the railcar unloading area due to the grade and flow pattern of the concrete pad on which the release would occur.   
Meteorological conditions for the alternative release scenario is atmospheric stability class D, wind speed of 3.0 meters per second, and ambient air temperature of 25 degrees C and 50 percent humidity.  Topography for the alternative release scenario is urban. 
Using these parameters it was determined (using EPA Offsite Consequence Analysis Guidance tables) that with a carbon disulfide release of 599.5 pounds, the estimated distance to the toxic endpoint of 0.16 mg/L is 0.17 miles. 
Although this scenario could occur, preventative maintenance, scheduled inspections of the equipment in the carbon disulfide process and continuous monitor 
ing by Viskase operator's help to identify and reduce the risk of this scenario from occurring.   
Viskase complies with the Process Safety Management rule of OSHA standard 29 CFR 1910.119 for the prevention of hazardous chemical releases.  The Process Safety Management Plan is a comprehensive program with fourteen elements, including process hazard analysis, employee training, operating procedures, mechanical integrity, pre-safety startup, contractor safety, emergency planning and response, compliance auditing, and employee participation.  The Process Safety Management Program ensures that the processes and the equipment in the processes are designed, constructed, and maintained according to industry codes and standards and that the processes are operating according to  good engineering practices.  The mechanical integrity element of the program includes scheduled inspections and tests of equipment and of monitoring devices in the process to detec 
t any deficiencies or defects in equipment.  Preventative maintenance and replacement policies of parts and equipment ensures that deficiencies are addressed and corrected before they could potentially contribute to a release incident.   All elements of the Process Safety Management Program help to ensure an uncontrolled release of carbon disulfide is prevented. 
No accidental releases of carbon disulfide have occurred at Viskase in the past five years. 
Viskase has developed an emergency response plan (in accordance with 29 CFR 1910.38) that includes provisions to evacuate employees from the facility in the event of an uncontrolled accidental release of a hazardous chemical.   It is Viskase's policy to contact the local emergency planning committee, and the local fire department in the event of a hazardous chemical release.  Viskase also conducts annual community drills with the local fire department, the local police departmen 
t and the local emergency response agency.  Viskase utilizes an emergency response group (Ferguson Harbor) that will respond to a hazardous chemical release and any cleanup operations.  Viskase has coordinated with the local emergency planning committee on its emergency response plan, and in the unlikely event of an uncontrolled release, the local emergency management agency will notify any affected neighbors or surrounding properties if an evacuation is necessary. 
Viskase is committed to continuous efforts to improve the safe operation of the carbon disulfide process by implementing preventative maintenance programs, inspection programs, and employee training in the safe operation of the equipment and the system.  The carbon disulfide process is designed in accordance with good engineering practices.  Periodic auditing of the Process Safety Management Prevention Program ensures that any system changes or modifications are evaluated and necessary sa 
fety precautions and or safety improvements are made before the process is placed into operation.
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