Hill Brothers Chemical Co. - Tucson facility - Executive Summary

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Hill Brothers Chemical Co. facility in Tucson, Arizona handles 150 pound cylinders and one-ton containers of chlorine for distribution to customers in southern Arizona. 
Hill Brothers Chemical Co. (HBC) developed this document to meet the requirements for a Program 3, Risk Management Plan (RMP) under the Accidental Release Prevention Program, Clean Air Act Amendments of 1990 for its chlorine storage and distribution  process located at 3602 East 34th Street, Tucson, Arizona. 
This RMP was prepared in accordance with the US Environmental Protection Agency (USEPA) requirements in 40 Code of Federal Regulations (CFR) Part 68. 
HBC prepared this RMP in conjunction with the Arizona branch of EMCON Environmental Associates (EMCON). 
The HBC Accidental Release Prevention & Emergency Response Policies 
The HBCs policy is to conduct all operations in a safe and conscientious manner to prevent accidental releases of any hazardous material, including substances regulated through the Federal Acc 
idental Release Prevention Program.  The HBC trains its employees at this facility to properly handle and store hazardous materials to minimize the possibility of adversely affecting its worker's health, the workplace, the public, and the environment. 
In the event of an emergency, HBC will contact the Tucson Fire Department to respond.  A designated emergency contact for the plant initiates emergency notifications.  All employees are trained in the proper procedures and their appropriate role in an emergency.  The Tucson plant maintains a highly cooperative relationship with the Tucson Fire Department to ensure a full understanding of the chlorine storage and emergency response and evacuation procedures related to regulated substances. 
General Description of Regulated Substance and Stationary Source 
The HBC's Tucson facility is located at 3602 East 34th Street, Tucson, Arizona.  The Tucson operation consists of a warehouse which stores liquefied chlorine and other materials.  HBC su 
pplies liquefied chlorine in pressurized containers to customers in the Tucson area. This warehouse is strictly a storage and distribution point for HBC; no processing or actual use of chlorine occurs at this facility. The North American Industrial Classification System (NAICS) code for this process is 422698, Other Chemical and Allied Products Wholesalers. 
Chlorine is a dense, greenish-yellow gas with a pungent, irritating odor.  Chlorine stored at the warehouse is contained in metal vessels designed to Department of Transportation standards.  Each chlorine container delivered, stored, and distributed at the warehouse has a steel valve protection cap which covers the container valve or valves.  These steel protective caps are never removed from the container and the container valves are never opened or operated in any way at the warehouse.  The containers are stored in a concrete building with a wood roof and a fire sprinkler system for fire protection. 
Off-Site Consequence Analyse 
s Results 
The RMP Program requires the evaluation of an accidental release of the regulated substance from the process being considered, in this case chlorine stored in the warehouse.  In its General Guidance for Risk Management Programs, July 1998, USEPA states that it should be kept in mind that the results obtained from modeling release scenarios should not be considered to predict the likely results of an accidental release.  The assumptions made in the computer models are very conservative and tend to overpredict the impact from an accidental release.  The results from such models have a high degree of uncertainty and should be viewed as providing a basis for discussion, rather than hard predictions.   
As required by USEPA for the RMP, the HBC assessed two types of release scenarios for the chlorine process.  The first scenario is a worst-case release which is mandated by USEPA to be the release of the largest quantity of a regulated substance that results in the greatest dist 
ance from the point of release to a specified endpoint (40CFR'68.3).  The second scenario is an alternative release scenario which is more likely to occur than the worst-case scenario and reaches an endpoint offsite. For chlorine, the specified endpoint is a concentration of 0.0087 milligrams of chlorine per liter of air.  This endpoint concentration is intended to be conservative and protective.  This is a concentration below which it is believed nearly all individuals could be exposed for up to one hour without any serious health effects.  Details of these two scenarios are presented below. 
Worst-Case Release Scenario 
USEPA requires that the worst-case release scenario be the release of the entire contents of the single largest vessel containing the regulated substance, in our case a container of chlorine.  USEPAs RMP*CompT model was used as the method for estimating the distance to the endpoint.  The RMP*CompT default values for release duration, wind speed, and atmospheric st 
ability class were utilized for this modeling.  These default values are very conservative in predicting the distance to the endpoint. 
The worst-case release scenario was designated as the release of 2,000 pounds of chlorine gas from a one-ton vessel at the facility.  This scenario allowed consideration that the release of chlorine gas to the outside air was slowed since these containers are located inside the warehouse.  No other containers are affected by this release scenario.  The distance from the site of the release to the endpoint extended beyond the boundaries of the Tucson facility.  Public receptors are located within this distance to the endpoint. 
Alternative Release Scenario 
The alternative release scenario gives us an opportunity to present a potential release impact which is more credible than the worst-case scenario.  However, it should be noted that given the safety and accident prevention mechanisms in place at Tucson, this alternative release scenario is not consid 
ered to be highly likely.  The RMP*CompT default values for release duration, wind speed, and atmospheric stability class were utilized for this modeling.  Once again, these values are very conservative.   
For the alternative release scenario it was assumed that a one-ton vessel stored in the warehouse developed a leak from a faulty valve mechanism.  Under this scenario the escaping chlorine gas cools rapidly as it expands from the container thus eventually freezing and closing the source of the leak.  In the presence of ambient temperature on the outside of the container, the frozen chlorine will eventually melt and allow additional chlorine gas to escape until the cycle repeats.  It is estimated that this intermittent release mechanism would allow a total of approximately 150 pounds of chlorine gas to be released into the interior of the warehouse.  The gas would then exit the building through doorways to the outside air.  HBC staff at the Tucson facility would evacuate the immediat 
e area and call the Tucson Fire Department to respond.  It is estimated that 30 minutes would transpire between the release starting and when Tucson Fire Department personnel would respond and stop the leak by installing a repair kit over the leaking valve. The distance from the site of the release to the endpoint extends beyond the boundaries of the Tucson facility.  Public receptors are located within this distance to the endpoint. 
Summary of the General Accidental Release Prevention Program & Chemical Specific Prevention Steps 
The HBC's release prevention program complies with Federal Accidental Release Prevention requirements for chlorine.  The HBC's prevention program emphasizes thorough training for its employees in hazard communication; proper handling, transfer, and storage methods; and awareness level emergency response.  HBC's standard operating procedures include diligent observation of chlorine vessels, valves, and other equipment; and safe movement and storage of chlori 
ne vessels.  The chlorine containers are designed and constructed in accordance with Department of Transportation requirements for safety. When stored in the warehouse, chlorine cylinders are chained upright in a metal rack to prevent them from falling over.  All chlorine containers at the warehouse have a steel valve protection cover to prevent the valve from being damaged.  These steel valve protection covers are never removed at the Tucson warehouse and container valves are never opened at the warehouse.  A fire suppression system is present in the building which consists of automatic sprinkler which are activated in case of a fire. 
Summary of Five-Year Accident History 
On the basis of a review with the HBC during preparation of this RMP, there have been no accidents or accidental releases involving chlorine at the Tucson facility in the last five years. 
Summary of the Emergency Response Program 
The HBC's Tucson facility has a written Emergency Response Plan.  The focus of the 
plan is to protect the public, protect employees, protect public property, and protect HBC facilities.  Immediately after discovering a release of chlorine, Tucson personnel are instructed to notify the Tucson Fire Department for initial response and evacuate the area affected by the release.  The Tucson Fire Department will be the primary responder to a chlorine release. 
Planned Changes to Improve Safety 
The HBC Tucson facility is continually evaluating ways to improve safety at the site.  Personnel that handle chlorine containers are trained and updated in the hazards of chlorine and proper safety, operating procedures, and emergency response.
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