To offer Intertek PARC’s pilot plant services to the (petro) chemical industry, PARC has started to use the Chemical Exposure Index (CEI) as calculated in Dow’s Chemical Exposure Index Guide [1]. The CEI is calculated from the estimated airborne release rate of the chemical compound of interest and its ERPG-2 value. The three Emergency Response Planning Guidelines (ERPG) are defined as [1]:
“ERPG-1 is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for one hour without experiencing other than mild transient adverse health effects or perceiving a clearly objectionable odor.”
“ERPG-2 is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for one hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair their abilities to take protective actions.”
“ERPG-3 is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for one hour without experiencing or developing life-threatening health effects.”
CEIs were calculated for a series of chemicals at a set of conservative conditions. The ERPG values of the chemicals were obtained from their Material Safety Data Sheets and were calculated as detailed in the guide. The chemicals were then grouped into four categories (A through D) according to their hazard level or CEI. As pointed out, “[a]bsolute measures of risk are very difficult to determine, but the CEI system will provide a method of ranking one hazard relative to another. It is NOT intended to define a particular design as safe or unsafe[1].” While Intertek PARC’s facility is substantially smaller than refineries or petrochemical plants, this index can still provide guidance in comparing new processes to current existing processes. Current operation has been mainly restricted to “Group A” chemicals. PARC does have extensive experience with hydrogen sulfide, a “Group B” chemical, since it is formed when hydrotreating crude oil. Hydrotreating operations producing hydrogen sulfide are typically at low effective hydrogen sulfide flow rates, reducing the hydrogen sulfide to a “Group A” chemical when considering emissions to the atmosphere.
It is important to realize that the CEI is defined for a vapor release to the atmosphere at a wind speed of 11.2 mph and at neutral weather conditions [1]. Intertek PARC’s P-84 pilot plant bank is located inside Building C4 at its Pittsburgh facility. Due to the pilot plants being located indoors, two releases exist. The first one is into the well-ventilated process area and the second one, as characterized by the CEI, is into the atmosphere via the Building C4 exhaust fans and blow down systems.
Independent layers of protection are required to safeguard the operator against potential hydrogen sulfide releases inside Building C4. An independent protection layer is defined “…as a device, system, or action that is a capable of preventing a scenario from proceeding to its undesired consequence independent of the initiating event or the action of any other layer of protection associated with the scenario [2].” Protection layers include a combination of process area hydrogen sulfide alarms, operator hydrogen sulfide monitors, airline respirators, cartridge respirators (for escape only), and alarms on the air handlers/ exhaust fans.
Learn more about Intertek PARC at: www.intertek.com/automotive/parc/
References:
1. AIChE, Dow’s Chemical Exposure Index Guide, 1st Edition, 1994.
2. AIChE, Layer of Protection Analysis, 2001.
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