Praxair - Walden, CO - Executive Summary
The Praxair facility at Walden, Colorado is a carbon dioxide purification plant. We receive carbon dioxide gas as a byproduct from a nearby natural gas well source. Normally, this carbon dioxide gas is vented to the atmosphere, but it is collected and transferred to our facility via pipeline. Praxair purifies and liquefies the carbon dioxide using a simple process of drying and distillation. The final liquid carbon dioxide product is stored in our insulated storage tanks, and is shipped by truck and railcar to customers throughout the west. |
As part of the carbon dioxide production process, the Walden facility uses a standard ammonia refrigeration process to purify and liquefy the carbon dioxide. Similar to the freon used in a home refrigerator, the ammonia is neither produced nor consumed in the process, but is repeatedly compressed, cooled and expanded in order to produce the cold temperatures necessary to cool and condense the carbon dioxide gas. Anhydrous ammonia is listed as
a regulated toxic substance in EPA's Risk Management Program rule, with a threshold quantity of 10,000 pounds. The refrigeration cycle at the Walden plant contains about 44,000 pounds of ammonia, and is therefore subject to the RMP rule.
Under the RMP rule, Praxair is required to report a Worst Case Scenario for the Walden plant, which is defined by the EPA as the release of the entire contents of the largest ammonia vessel in our process. We are not required to identify a possible cause of this worst case release, but rather assume that it takes place, and that essentially none of the safety systems and devices that are in place to prevent such an occurrence function as designed. The release is assumed to occur over a 10 minute time period, and under the most stable atmospheric and weather conditions, which minimizes the dispersion and dilution of the release and presents the absolute worst case that could possibly occur. Given all of these conditions, we are then required to es
timate the distance to an EPA-specified toxic endpoint, which is defined to be a concentration of 200 ppm for ammonia. At the Walden facility, the largest ammonia vessel contains about 8,500 pounds. Using the criteria listed above, the Worst Case Scenario would result in a maximum downwind distance of about 1.7 miles to the EPA-specified endpoint. To determine this distance, we used the EPA's "Risk Management Program Guidance for Ammonia Refrigeration."
We are also required to report an Alternative Release Scenario, or planning scenario, under the RMP rule. While an Alternative Release may never occur at a facility, it is generally accepted to be more likely, or more credible, than the Worst Case Scenario, and can be used by the facility and local response organizations to plan community emergency response activities. The RMP rule assumes more typical atmospheric and weather conditions for an Alternative Release Scenario, and allows a facility to take credit for safety devices an
d other mitigation systems that are in place to minimize the likelihood and effects of a release. When selecting an Alternative Release Scenario, EPA suggests a facility consider scenarios such as transfer hose releases, valve and flange leaks, pump seal leaks, and shipping container mishaps, among others. For a typical ammonia refrigeration process, all of these scenarios would be equivalent to a release from a small hole (1/4" diameter) in a tank or pipe containing ammonia at the highest system pressure. At the Walden facility, a release of this type would result in a maximum downwind distance of about 0.2 miles, or 1,060 feet. To determine this distance, we used the EPA's "Risk Management Program Guidance for Ammonia Refrigeration."
In accordance with OSHA's Process Safety Management standard and EPA's Risk Management Program rule, the Walden facility has a comprehensive accident prevention program in place to ensure the safety of our employees, our neighbors and the community
around us. On a local level, this prevention program is built around process safety concepts such as:
7 Documented process safety information to ensure the process design is understood and maintained throughout its life;
7 Process hazard analysis to identify and control all of the hazards associated with handling anhydrous ammonia;
7 Trained operators, using written operating procedures, to safely operate the process as intended; and
7 Maintenance programs and procedures to ensure the on-going mechanical integrity of the process.
The prevention program is audited periodically, by our corporate assessment group, to ensure that the process safety concepts and practices are in place and working effectively.
As a result of our process safety and risk management practices, the Walden facility has not had an accident involving ammonia in the last five years. In the event of an emergency, the facility has an emergency action plan in place, which contains procedures for employees to follo
w, including notification of local response agencies. All facility employees are trained in their role in the emergency action plan, and Praxair policy requires that emergency drills be conducted at least annually.
Praxair is committed to continuous improvement of its safety and environmental programs. At the Walden facility, we have recently installed additional atmospheric monitoring equipment, for both ammonia and carbon dioxide, to ensure the safety of our employees and the community, and enhance our capability of detecting minor releases before they can become major events. Upcoming changes to improve the safety of the plant include plans for an ammonia absorption tank that will further minimize the effects of controlled releases of ammonia due to process upsets and maintenance activities.
Praxair is a producer and distributor of industrial gases with almost 100 years of experience. We are committed to being the best performing industrial gas company in all aspects of our bu
siness, including safety, health and environmental affairs. Praxair is a member the Chemical Manufacturers Association's Responsible Care initiative, which is intended to ensure the safe operation of chemical facilities and enhance the relationships between the chemical industry and the communities in which we operate. Internally, we use a combination of extensive engineering standards and design safety work processes, coupled with operational and personnel safety programs, to ensure the safe operation of all of our facilities. Our company-wide goal of "Zero/Zero" (which means zero accidents and zero injuries or illnesses at every location) reflects the dedication and commitment to safety throughout the entire Praxair organization.