Overview
The District has created a health risk assessment (HRA) screening tool spreadsheet for diesel-fired internal combustion engines (DICE), titled DICE Screening Tool.xlsx. This spreadsheet calculates conservative cancer risk and chronic non-cancer risk due to diesel particulate matter (PM) emissions from DICE. This tool was created to reduce the amount of time required to conduct HRAs for DICE permits. The District has also published a user guide for the tool.
The user must input the following information into the spreadsheet: appropriate meteorological data set, dispersion type (urban or rural), whether or not to include building downwash effects, engine rating, the diesel PM emission factor, maximum hours of operation, and the distance from the engine to the nearest resident and nearest worker. An example input table is shown below.
The DICE Screening Tool was created using the Non-Vehicular Diesel Engine Risk Assessment Screening Tool developed by the California Air Pollution Control Officer’s Association (CAPCOA) and the California Air Resources Board (CARB). More information can be found in the District’s Background Document for DICE Screening Tool.
Acute and 8-Hour Chronic Non-Cancer Risk
Because diesel PM does not have an acute or 8-hour reference exposure level, the only way to calculate the acute or 8-hour risk for a DICE is to calculate the emissions of speciated pollutants in diesel exhaust. Because these speciated pollutants are components of diesel exhaust, their annual emissions are not used for cancer and chronic non-cancer risk determination, as this would overestimate the cancer and chronic non-cancer risk.
The available speciated pollutant emission factors for DICE are based on source testing performed on Tier 0 engines in the early 1990s. The USEPA emission standards for diesel engines have become much more stringent since this time. Therefore, these factors are not representative of Tier 3 and Tier 4 engines, and Tier 2 engines greater than 750 bhp. At this time, the District has not determined representative emission factors for newer engines. For this reason, the acute and 8-hour HIs are not required to be evaluated for new diesel engines. Once representative emission factors have been identified for newer engines, the DICE Screening Tool will be updated with those factors.
Other Information
- More information about diesel engines is available on the District’s Diesel Internal Combustion Engine (DICE) Air Toxic Control Measure webpage.
- Detailed requirements on performing health risk assessments are included in the District’s Modeling Guidelines for Health Risk Assessments, Form -15i.