What does Inherently Safer Mean?

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In a lethal process safety incident in 2007 in Frankfurt, Germany, an operator at a tank farm accidentally fed hydrochloric acid (HCl) to a sodium hypochlorite (NaOCl) storage tank. The combination of chemicals liberated chlorine gas. The operator successfully managed to limit the quantity of chlorine gas released to 200 kg, but died of acute chlorine exposure a month after the incident. Over sixty people were harmed by the liberated gas.
filling Station Road Tankers
Figure 1. Schematic for filling storage tanks at Frankfurt facility

An investigation of the incident revealed that tank filling operations were conducted according to the schematic in Figure 1. As the schematic shows, the farm housed storage tanks for NaOCl, FeCl3, and various other acids and hydroxides. At the delivery station for tankers, there was a single hose for feeding the FeCl3 tank and a single hose for feeding any of the other storage tanks. All adapters at the battery were equipped with similar threads. Samples from the road tanker were analyzed in a laboratory at the facility before filling any of the tanks. Propose at least two inherently safer technologies for any aspect of the process/schematic. Assign a design level to your idea (see the end of the article), and justify your decision in 1-2 sentences.
  • Add a separate hose for hypochlorite, in order to prevent/minimize the addition of acids to the hypochlorite tank (and consequent chlorine gas liberation). This constitutes a second-order ISD. (Chlorine gas formation is still possible, if an operator somehow feeds HCl through the hypochlorite hose in the future.)
  • Equip the hypochlorite adapter with different size or type of connector (from that of the acid adapters), so that any hose for conveying acids will be incompatible with the hypochlorite adapter. A similar ISD occurs at the gas pump – you cannot fill a diesel gas tank with regular unleaded fuel because the nozzle will not fit in the opening. The same is true for trying to fill a regular unleaded gas tank with diesel. This ISD is second-order, for the same reason as above.
  • Hoses should never be swapped at all and dedicated hoses for each storage tank should remain connected at the storage tank itself and never be removed. This minimizes the potential for incorrect connection. The risk still exists to connect the incorrect hose to the tanker, but the ISD modifications listed above can prevent this from occurring. This ISD is second-order.
List three examples of inherently safer technology (IST) that should be used in the chemical engineering workplace.

All facilities in the chemical industry should have proper fire mitigating infrastructure such as automatic sprinklers and alarms. Looking at many CCPS Beacon articles has revealed that this isn’t as common as it needs to be. All facilities should also have proper Management of Change procedures in place. A lot of incidents happen when operations change or during shift changes, so these situations should be protected the best they can. All facilities should have adequate temperature monitors in their tanks. Many CCPS Beacon articles discuss exploding tanks with mismanaged or broken temperature reading of the tanks. Many disasters occur when alarms were ignored or when alarms were missing in the control room or on the plant floor. Specific procedures should be in place whenever an alarm occurs. The cause of the alarm should be verified and checked against other diagnostic data, action should be taken if necessary, and the process shut down if there is a serious risk. Wherever alarms are needed, they should be implemented based on appropriate operating limits, and hazard and safety evaluation.

An experienced chemical engineer working for Dow Chemical, you have been appointed to the risk assessment team for the design of a new pesticide production plant. Explain the factors you would consider during the risk assessment process. Consider specifically who is impacted by this assessment and how risk can be minimized for all relevant parties. Suggest at least two resources for defining suitable risk-reduction criteria. Your response should comprise 4-5 sentences.

The risk assessment of the new plant design must evaluate and resolve conflicts among process safety hazards; potential impacts of process safety incidents to neighboring communities, businesses, and the environment; technical and environmental feasibility; and impacts on process safety in other industries or in various aspects of the production life-cycle. Conflicts are often difficult to resolve—and resolution often involves various tradeoffs—because optimizing the process design to minimize any given hazard may augment the risks associated with another hazard. Moreover, different approaches to risk assessment may yield varying conclusions on the safety and effectiveness of the plant design. Expectations for risk management are heavily contingent upon what the local society deems acceptable. It may therefore be helpful to reference documentation on local government regulations, corporate standards, and consensus codes to determine suitable risk-reduction criteria and facilitate the risk assessment.