Petroleum Refinery Sector Risk and 

Technology Review

Presentation to the U.S. EPA Science Advisory Board

July 19, 2013
Overview

► Exposure and Risk Assessment Process

► Refinery Emissions: Inventories and Emission Sources

► Monitoring Approaches

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16. 3

Planning and Scoping

Exposure Assessment Toxicity Assessment

Risk Characterization

Quantitative and Qualitative Expressions of Risk/Uncertainty

POPULATION CHARACTERISTICS

Measures of 

Exposure

CHEMICAL

CONCENTRATIONS

Air, Soil, Water, Food

(monitor/model)

Human Risk Assessment Process

Dose/ 

Response 

Assessment

Y

X

Chemical 

Release SOURCES

FATE AND TRANSPORT ANALYSIS

 Hazard Identification

EXPOSURE 

information

DOSE/RESPONSE 

information

SOURCE IDENTIFICATION

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Estimating Inhalation Risks under the Risk 

and Technology Review Program

For the inhalation pathway, the concentration (C) of the chemical 

in air (in ug/m3) at the point of exposure (called the exposure 

concentration or EC) can be used as a measure of exposure

For chronic inhalation exposure, 

usually use an estimate of annual 

arithmetic average concentration 

at census blocks centroids to 

represent the long-term EC

The basic equations for calculating risk from 

breathing air toxics is:

Cancer Risk = EC x URE

Noncancer Hazard Quotient = EC /RfC

Where:

EC = concentration of the chemical in air at the point of exposure (ug/m3)

URE = Unit Risk Estimate (risk/ug/m3)

RfC = Reference Concentration in (ug/m3)

For acute inhalation exposure, 

usually use an estimate of 

highest 1-hour ambient 

concentrations at or near the 

facility fenceline to represent the 

short-term EC

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Developing Exposure Estimates

► We use the EPA Human Exposure Model (HEM) risk 

modeling system to estimate exposure, which contains:

► AERMOD dispersion model (EPA’s approved local-scale model)

► 2010 Census data at census block resolution (about 10 households)

► Terrain elevation data

► Meteorological data

• Uses historical (2011) data from weather stations nationwide

► Exposure estimates are conservative

► We assume that there is a person at the centroid of census block 

who is continually exposed for 70 years 

• If the highest concentration is at residence closer to the facility than the 

centroid, we use that concentration as our exposure estimate 

► This reflects the Clean Air Act mandate to assess risks to the 

‘individual most exposed’

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Human Health Benchmarks

► RTR assessments includes benchmarks developed from EPA (IRIS) 

and other peer reviewed sources (ATSDR, CALEPA), and is compiled 

and maintained by EPA air program toxicologists 

http://www.epa.gov/ttn/atw/toxsource/summary.html

► Cancer (URE) -- Noncancer (RfC) -- Acute (REL, AEGL, ERPG)

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Inhalation Risk Outputs

► Chronic 

► Cancer: Maximum Individual Risk (MIR) – highest cancer risk (in a 

million) at a location where people live (census block centroid or nearest 

residence)

► Noncancer: Hazard Index (HI) – highest noncancer risk at a location 

where people live (census block centroid or nearest residence)

► Annual cancer incidence (cases/year)

► Cancer risk bin distributions (>100 in a million, 10 in a million...)

► Source category and facility wide risks

► Process level risk contributions

► Acute

► Maximum off-site impact: pollutant-specific highest 1-hour Hazard 

Quotient (HQ) outside estimated facility fenceline

• Default factor of 10x time the annual emissions rate unless source category 

specific information is provided

• Can be refined with site-specific boundary conditions

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Development of Emission Inventories

► The purpose of the risk and technology review is to evaluate the 

MACT standards to determine if:

► It is necessary to tighten the standards to protect human health and 

the environment with an “ample margin of safety”

► There are advancements in practices, processes or technologies that 

warrant tightening the standards

► Risk and technology review requires emission inventory data

► Emission inventories are developed to satisfy state requirements

► EPA provides guidance in the form of AP-42 emission factors, but 

does not mandate their use

► Inventories are not consistent among states

► Speciation and completeness of data for air toxic pollutants vary

► EPA houses state inventories in the Emission Inventory System (EIS)

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Refinery Emissions Inventory

► EPA was petitioned in 2008 under the Data Quality Act to improve emission 

factors from refineries

► In response, EPA developed a refinery emissions estimation protocol, which was 

put through two rounds of public notice and comment in 2010

• http://www.epa.gov/ttn/chief/efpac/protocol/index.htm

► Refinery Emissions Estimation Protocol

► Provides consistent set of methods for estimating emissions (criteria pollutants 

and air toxics)

► Requires speciation of air toxic pollutants

► Describes what refinery emission sources should have pollutant emission 

estimates

► No new sampling is required

► Ranking of methodologies depending on available data

► More detailed and comprehensive than AP-42 emission factors

► 2011 Refinery ICR required refiners to use the Refinery Emissions 

Estimation Protocol to develop their inventory

► Refinery inventory submitted in response to the ICR will be used to perform 

the risk and technology review of the MACT standards

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Air Toxics Emissions from Refineries

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Petroleum Refinery HAP Emissions

Source: 2011 ICR

Equipment Leaks

Cooling Towers

Wastewater Treatment

Flares

Storage

Misc Processes

FCCU

Combustion

“Fugitive" sources account 

for half of the air toxics 

inventory and most of the 
Refinery Emission Sources

► Point sources (vents or stacks)

► Emissions generally well understood and well characterized, and some test data available where 

pollutants were directly measured

► Examples include vents at catalytic cracking, fluid coking, delayed coking, catalytic reforming, 

sulfur recovery, hydrogen plants

► As part of risk and technology review, EPA is amending rules to require electronic submission of 

performance test data; will be used to periodically update emission factors

► Flares

► Destruction of pollutants in an open flame

► Difficult to directly measure pollutants

► Flare studies available to develop correlations for parameters that affect flare destruction 

efficiencies (2012 peer review)

► September 2012 NSPS flare amendments will require all flares to eventually have monitors to 

measure waste gas flow

► Flare operational requirements ensure good combustion and provide information (waste gas 

composition and flare destruction efficiency) that can be used to estimate emissions from flares

► Fugitive emission sources

► Tend to be open sources or not emitted through a stack or vent, thus difficult to directly measure 

pollutants

► Examples include equipment leaks and pressure relief devices, tanks and transfer operations and 

wastewater handling and treatment

► Emission models and estimates are used to predict pollutant emissions

► An emission standard at the fenceline can help ensure fugitive emission standards are being met

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Fenceline Monitoring

► Fugitive emission sources may not be well characterized in the inventories but are likely 

significant contributors to overall emissions

• Fugitives from process piping

• Wastewater sources

• Pressure relief events

• Tanks

► Highest concentrations of these fugitive emission sources outside the facility likely occur 

by the property boundary near ground level

► Air monitoring at the property boundary can provide a direct measure of the annual 

average concentrations of air toxics directly surrounding the refinery

► Benzene is a refinery risk driver and also primarily emitted from fugitive sources; 85% of 

benzene emissions from refineries is from fugitive, ground-level sources, so reducing 

emissions of benzene from fugitive sources will reduce emissions of other toxic pollutants

► Perimeter or fenceline monitoring provides an indicator of the level of emissions at 

refineries and is a way to ground-truth fugitive emission estimates

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Low-cost 

sensor 

networks

Different technologies and approaches to detect and measure

pollutants over extended areas and time 

Mobile 

inspection 

systems

Monitoring for Assessment of Fugitives

Leak detection power and feasibility of widespread deployment

Analytical power and implementation cost 

Current openpath and auto 

GC systems

Lower cost 

optical 

systems

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0.2 0.5 2 5 10 (μm)

UV DOAS TDL FLIR FTIR

UV Diff. Optical 

Absorption 

Spectroscopy 

Tunable Diode 

Laser (scanning)

Forward-Looking 

InfraRed 

(leak imaging)

Fourier Transform 

InfraRed (scanning)

Open-path 

optical 

systems

Open-Path Instruments

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N

Low-Cost Sensors Can Provide 24-7 Observation and 

Enable New Regulatory Approaches

Passive sampling Facility fenceline monitoring

Low-cost 

sensor 

networks

• Locate passive samplers around the 

perimeter of each refinery

• Calculate annual average concentration

• If rolling average concentration exceeds 

benzene concentration standard (the action 

level), initiate tiered approach to positively 

identify facility contribution and conduct 

corrective action to reduce emissions

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Developments in Lower-Cost Time-Resolved Monitoring to Support 

Time-Integrated Passive Sampler Fenceline Measurements

Mobile inspection 

systems 

SECONDARY 

MIRROR

PRIMARY 

MIRROR

SEALED UV 

WINDOW

BEAM 

SPLITTER

DETECTORS

FOCUSING 

LENS Lower cost 

open-path 

optical 

systems

Deep UV optical sensor

Drive-by leak inspection

Drop-in-place sensor packages

Prototype PID sensor package 

(pres. temp. , RH., VOC)

Combining 

senor and 

wind data

New leak-location algorithms

Low-cost 

stand-alone 

sensors

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Wind

April 2013 passive sampler and GMAP demo with a cooperating refinery

Mobile inspection detected benzene leak at location of the highest passive sampler reading

Passive 

sampler 

Geospatial measurement 

(GMAP) mobile benzene 

survey

Passive sampler fenceline and mobile inspection demonstration 

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