October 9, 1997

Placer County APCD 231 - 1 Rules and Regulations

RULE 231 INDUSTRIAL, INSTITUTIONAL, AND COMMERCIAL BOILERS, 

 STEAM GENERATORS, AND PROCESS HEATERS

 Adopted 10-17-94 

(Amended 10-9-97) 

 CONTENTS

100 GENERAL

101 PURPOSE 

102 APPLICABILITY 

103 EXEMPTIONS, 

200 DEFINITIONS

201 ANNUAL HEAT INPUT 

202 BOILER OR STEAM GENERATOR 

203 BRITISH THERMAL UNIT (BTU) 

204 GAS 

205 HEAT INPUT 

206 HIGHER HEATING VALUE (HHV) 

207 MUNICIPAL SOLID WASTE 

208 NOx EMISSIONS (NOx) 

209 NONGASEOUS FUEL 

210 PARTS PER MILLION BY VOLUME (PPMV) 

211 PROCESS HEATER 

212 RATED HEAT INPUT CAPACITY 

213 RESPONSIBLE OFFICIAL 

214 STANDARD CONDITIONS 

215 THERM 

216 UNIT 

300 STANDARDS

301 ANNUAL HEAT INPUTS  90,000 THERMS 

302 ANNUAL HEAT INPUTS < 90,000 THERMS 

303 EQUIPMENT REQUIREMENTS 

400 ADMINISTRATIVE REQUIREMENTS

401 COMPLIANCE SCHEDULE 

402 COMPLIANCE DETERMINATION 

403 COMPLIANCE COSTS 

404 CERTIFICATION 

500 MONITORING AND RECORDS

501 FUEL USAGE AND OPERATING HOURS 

502 SOURCE TESTS 

503 TUNING REPORTS 

504 RETENTION OF RECORDS 

600 TUNING PROCEDURE

601 GENERAL 

602 PROCEDURES 
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Rules and Regulations 231 - 2 Placer County APCD 

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Placer County APCD 231 - 3 Rules and Regulations

100 GENERAL 

101 PURPOSE: To limit the emission of Nitrogen Oxides (NOx) from industrial, institutional and 

commercial, boilers, steam generators and process heaters. 

102 APPLICABILITY:

102.1 Geographic: The provisions of this rule apply to facilities in all of Placer County. 

102.2 General: This rule applies to boilers, steam generators, and process heaters with 

rated heat inputs of equal to or greater than 5 million BTU per hour, used in 

industrial, institutional, and commercial operations. 

103 EXEMPTIONS:

103.1 Exemption, Biomass Boilers: The provisions of this rule do not apply to boilers 

subject to Rule 232, Biomass Suspension Boilers , or Rule 233, Biomass Boilers. 

103.2 Exemption, Cement and Lime Kilns, Glass Melting Furnaces, and Smelters: The 

provisions of this rule do not apply to cement and lime kilns, glass melting furnaces 

and smelters. 

103.3 Exemption, Direct-Contact Dryers: The provisions of this rule do not apply to dryers 

in which the material being dried is in direct contact with the products of combustion. 

103.4 Exemption, Electric Utility Boilers: The provisions of this rule do not apply to boilers 

used by electric utilities to generate electricity. 

103.5 Exemption, Medical Waste Incinerators: This rule shall not apply to those 

incinerators which are subject to the requirements of Rule 906, Airborne Toxic 

Control Measure - Medical Waste Incinerators 

103.6 Exemption, Municipal Waste Incinerators: This rule shall not apply to boilers, steam 

generators, or process heaters whose primary purpose is to burn municipal solid 

waste, as defined in Section 206. 

103.7 Exemption, Nongaseous Fuels: Units subject to the requirements of Section 301 that 

normally burn only gaseous fuel shall comply with a 150 ppmv, or 0.215 pound per 

million BTU of heat input, NOx emission limitation when burning nongaseous fuel, if 

gas is unavailable for purchase. This exemption is limited to not more than 168 

hours of operation per calendar year, excluding equipment and emission testing time 

not exceeding 48 hours per calendar year. 

103.8 Exemption, Waste Heat Recovery Boilers: The provisions of this rule do not apply to 

waste heat recovery boilers that are used to recover sensible heat from the exhaust 

of combustion turbines. 

200 DEFINITIONS

201 ANNUAL HEAT INPUT: The total heat input of fuels burned by a unit in a calendar year, as 

determined from the higher heating value and cumulative annual usage of each fuel. 

202 BOILER OR STEAM GENERATOR: Any combustion equipment fired with any fuel and 

used to produce steam that is not used exclusively to produce electricity for sale. 

203 BRITISH THERMAL UNIT (BTU): The amount of heat required to raise the temperature of 

one pound of water from 59F to 60F at one atmosphere. 

204 GAS: Any fuel which is a gas at standard conditions. 
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Rules and Regulations 231 - 4 Placer County APCD 

205 HEAT INPUT: The chemical heat released due to fuel combustion in a unit, using the higher 

heating value of the fuel. This does not include the sensible heat of incoming combustion air. 

206 HIGHER HEATING VALUE (HHV): The total heat liberated per mass of fuel burned (BTU 

per pound), when fuel and dry air at standard conditions undergo complete combustion and 

all resultant products are brought to their standard states at standard conditions. HHV shall 

be determined by one of the following test methods: 

206.1 ASTM D 2015-85 for solid fuels; or 

206.2 ASTM D 240-87 or ASTM D 2382-82 for liquid hydrocarbon fuels; or 

206.3 ASTM D 1826-88 or ASTM D 1945-81 in conjunction with ASTM D 3588-89 for 

gaseous fuels. 

207 MUNICIPAL SOLID WASTE: Household, commercial/retail, and/or institutional waste. 

Household waste includes material discarded by single or multiple residential dwellings, 

hotels, motels, and other similar permanent or temporary housing establishments or facilities. 

Commercial/retail waste includes material discarded by stores, offices, restaurants, 

warehouses, non-manufacturing activities at industrial facilities, and other similar 

establishments or facilities. Institutional waste includes material discarded by schools, 

hospitals, prisons, and government facilities and other similar establishments or facilities. 

Municipal solid waste does not include landfill gas or digester gas or other fuels derived from 

decomposition of municipal solid wastes. 

208 NOX EMISSIONS (NOX): The sum of nitric oxides and nitrogen dioxide in the flue gas, 

collectively expressed as nitrogen dioxide (NO2). 

209 NONGASEOUS FUEL: Any fuel which is not a gas at standard conditions. 

210 PARTS PER MILLION BY VOLUME (PPMV): The ratio of the number of gas molecules of a 

given species, or group, to the number of millions of total gas molecules. 

211 PROCESS HEATER: Any combustion equipment fired with any fuel, and which transfers 

heat from combustion gases to water or process streams. 

212 RATED HEAT INPUT CAPACITY: The heat input capacity, in million BTU per hour, 

specified on the nameplate of the combustion unit. If the combustion unit has been altered or 

modified such that its maximum heat input is different than the heat input capacity specified 

on the nameplate, the maximum heat input shall be considered as the rated heat input. 

213 RESPONSIBLE OFFICIAL: An individual with the authority to certify that a source complies 

with all applicable requirements, including the conditions of permits issued to sources in 

accordance with Regulation 5, PERMITS. A "responsible official" means one of the following: 

213.1 For a corporation, a president, secretary, treasurer, or vice-president of the 

corporation in charge of a principal business function, or any other person who 

performs similar policy or decision-making functions for the corporation, or a duly 

authorized representative of such person if the representative is responsible for the 

overall operation of one or more manufacturing, production, or operating facilities 

applying for or subject to a permit and either: 

a. The facilities employ more than 250 persons or have gross annual sales or 

expenditures exceeding $25 million (in second quarter 1980 dollars); or 

b. The delegation of authority to such representative is approved in advance by the 

Air Pollution Control Officer; 

213.2 For a partnership or sole proprietorship, a general partner or the proprietor, 

respectively; or 
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Placer County APCD 231 - 5 Rules and Regulations

213.3 For a municipality, state, federal, or other public agency, either a principal executive 

officer or a ranking elected official; or 

214 STANDARD CONDITIONS: For purposes of this rule, a gas temperature of 68 Fahrenheit 

and a gas pressure of 14.7 pounds per square inch absolute. 

215 THERM: One hundred thousand (100,000) BTU. 

216 UNIT: Any boiler, steam generator or process heater as defined in Sections 202 and 211. 

300 STANDARDS

301 ANNUAL HEAT INPUTS  90,000 THERMS: For units with rated heat inputs of greater than 

or equal to 5 million BTU per hour and annual heat inputs of greater than or equal to 90,000 

therms per year , NOx emissions shall not exceed the following levels: 

301.1 30 parts per million by volume (ppmv), or 0.036 pound per million BTU of heat input 

when operated on gas; or 

301.2 40 parts per million by volume (ppmv), or 0.052 pound per million BTU of heat input, 

when operated on nongaseous fuel; or 

301.3 The heat-input weighted average of the limits specified in 301.1 and 301.2, above, 

when operated on combinations of gas and nongaseous fuels. 

301.4 Emissions from units subject to this section shall not exceed a carbon monoxide 

concentration of 400 parts per million by volume (ppmv). 

302 ANNUAL HEAT INPUTS < 90,000 THERMS: Units with rated heat inputs of greater than or 

equal to 5 million BTU per hour and annual heat inputs of less than 90,000 therms per year 

shall be: 

302.1 Operated in a manner that maintains stack-gas oxygen concentrations at less than or 

equal to 3.00 percent by volume on a dry basis; or 

302.2 Operated with a stack-gas oxygen trim system set at 3.00 percent by volume oxygen. 

The tolerance of this setting shall be plus or minus () five percent (i.e. 2.85 to 3.15 

percent by volume oxygen); or 

302.3 Tuned at least once per year by a technician that is qualified, to the satisfaction of the 

Air Pollution Control Officer, to perform tuning in accordance with Section 600; or 

302.4 Operated in compliance with the applicable emission levels specified in Section 301. 

303 EQUIPMENT REQUIREMENTS:

303.1 For units which simultaneously fire combinations of different fuels, and are subject to 

the requirements of Section 301, non-resettable totalizing mass flow rate meters shall 

be installed in each fuel line. Alternatively, non-resettable totalizing volumetric flow 

rate meters may be installed in conjunction with temperature and pressure meters in 

each fuel line. 

303.2 For units which employ flue-gas NOx reducing technology, and are subject to the 

requirements of Section 301, meters, as applicable, shall be installed to allow 

instantaneous monitoring of the operational characteristics of the NOx reduction 

equipment. 
400 ADMINISTRATIVE REQUIREMENTS

401 COMPLIANCE SCHEDULE:

401.1 By January 1, 1995, any person subject to this rule shall submit a plan containing the 

following: 

a. A list of all units with their rated heat inputs and anticipated annual heat inputs. 

b. For each unit subject to Section 301, the selected method of achieving 

compliance with the applicable standards of Section 301. 

c. For each unit subject to Section 302, the selected option (one of four specified in 

Section 302) to achieve compliance with that section. 

401.2 By May 31, 1995, any Major Source subject to this rule shall demonstrate final 

compliance with all applicable standards and requirements of Section 300. Subject 

to the approval of the Air Pollution Control Officer, testing conducted in the 18 months 

preceding May 31, 1995, may be used to demonstrate compliance provided such 

testing meets the requirements of Sections 502.1, using the test methods specified in 

Section 502.3. 

401.3 By October 17, 1996, any non-Major Source subject to this rule shall submit an 

application for Authority to Construct for any modifications required to achieve 

compliance with the requirements of this rule. 

401.4 By October 17, 1997, any non-Major Source subject to this rule shall demonstrate 

final compliance with all applicable standards and requirements of this rule. 

401.5 Any non-Major Source subject to this rule installing a new or replacement boiler shall 

comply with this rule for the new or replacement boiler effective October 17, 1995. 

401.6 A violation of the plan required under Section 401.1 shall constitute a violation of this 

rule. 

402 COMPLIANCE DETERMINATION:

402.1 Any person subject to this rule shall have the option of complying with either the 

pounds-per-million-BTU emission rates or the parts-per-million-by-volume emission 

limits specified in Section 301. 

402.2 All ppmv emission limits specified in Sections 106 and 301 are referenced at dry 

stack-gas conditions and 3.00 percent by volume stack-gas oxygen. Emission 

concentrations shall be corrected to 3.00 percent oxygen as follows: 

NOx [ppm x ] [% - 20.95% O ]

3.00% - 20.95% NOx [ppm ] = measured

2 measured

corrected

CO [ppm x ] [% - 20.95% O ]

3.00% - 20.95% CO [ppm ] = measured

2 measured

corrected

402.3 All pounds-per-million-BTU emission rates shall be calculated as pounds of nitrogen 

dioxide (NO2) per million BTU of heat input. 

403 COMPLIANCE COSTS: A person operating a unit subject to this rule shall bear all expenses 

associated with compliance with the monitoring and reporting provisions of this rule. 

404 CERTIFICATION: All reports submitted in accordance with this rule shall be signed by a 

responsible official who shall certify the truth, accuracy, and completeness of the report. 

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Rules and Regulations 231 - 6 Placer County APCD 
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Placer County APCD 231 - 7 Rules and Regulations

500 MONITORING AND RECORDS

501 FUEL USAGE AND OPERATING HOURS

501.1 Any person subject to this rule shall monitor and record for each unit the HHV and 

cumulative annual usage of each fuel. 

 501.2 The cumulative annual usage of each fuel shall be monitored from utility service 

meters, purchase, or tank fill records, or by any other acceptable methods approved 

by the Air Pollution Control Officer. 

501.3 Any person subject to this rule, but exempt from Section 301 in accordance with 

Section 106, shall monitor and record for each unit the cumulative hours of operation 

on each nongaseous fuel. The records shall be updated weekly and made available 

to the District upon request. 

502 SOURCE TESTS

502.1 Except for units in compliance with the tuning option of Section 302.3, a source test 

shall be conducted for all units subject to this rule to demonstrate compliance. A 

report of this source test shall include the operational characteristics of any flue-gas 

NOx reduction equipment. Additional source testing may be required by the Air 

Pollution Control Officer as necessary to ensure compliance with the standards set 

forth in Sections 301 and 302. Compliance source testing is required on an annual 

basis for sources subject to Rule 507, FEDERAL OPERATING PERMIT PROGRAM. 

502.2 All source tests shall be made in the as-found operating condition, except that source 

tests shall include at least one test conducted at the maximum firing rate allowed by 

the District permit, and no source test shall be conducted within two hours after a 

continuous period in which fuel flow to the unit is zero, or shut off, for thirty minutes or 

longer. A separate source test shall be conducted for each fuel burned including 

standby fuel. 

502.3 Compliance with NOx emission requirements and the stack-gas carbon monoxide 

and oxygen requirements of Section 300 shall be determined using the following test 

methods: 

a. Oxides of Nitrogen - ARB Method 100, Title 17, CCR, Section 94114, Procedures 

for Continuous Emission Stack Sampling. 

b. Carbon Monoxide - ARB Method 100. 

c. Stack-Gas Oxygen - ARB Method 100. 

d. NOx Emission Rate (Heat Input Basis) - EPA Method 19, 40 CFR Part 60, 

Appendix A. 

502.4 All emission concentrations and emission rates shall be based on 15-consecutiveminute averages. These averages shall be calculated from no less than five data 

sets, recorded from samplings on intervals of no greater than three minutes. 

502.5 Integrated sampling methods for oxides of nitrogen, stack-gas oxygen, and stack-gas 

carbon monoxide, as approved by the Air Pollution Control Officer, EPA and ARB, 

may be acceptable for determination of compliance with NOx emission concentration 

or rate limits. 

503 TUNING REPORTS: Units covered under Section 302.3 shall be tuned not less than once 

every 12 months. Tuning verification reports shall be submitted not less than once every 12 
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Rules and Regulations 231 - 8 Placer County APCD 

 

months for each fuel burned. The first tuning verification report shall be submitted by October 

17, 1997, for non-Major Sources, and by May 31, 1995, for Major Sources subject to this rule. 

504 RETENTION OF RECORDS: All records maintained pursuant to this rule shall be retained 

for at least three years from date of entry, with the exception that sources subject to the 

requirements of Rule 507, FEDERAL OPERATING PERMIT PROGRAM, shall retain records 

at least five years. Records shall be made available for inspection by the Air Pollution 

Control Officer upon request. 

600 TUNING PROCEDURE

601 GENERAL: Nothing in this tuning procedure1

 shall be construed to require any act or 

omission that would result in unsafe conditions or would be in violation of any regulation or 

requirement established by Factory Mutual, Industrial Risk Insurers, National Fire Prevention 

Association, the California Department of Industrial Relations (Occupational Safety and 

Health Division), the Federal Occupational Safety and Health Administration, or other 

relevant regulations and requirements. 

602 PROCEDURES:

601.1 Operate the unit at the firing rate most typical of normal operation. If the unit 

experiences significant load variations during normal operations, operate the unit at 

its average firing rate. 

601.2 At the firing rate established in Section 601.1, record stack-gas temperatures, oxygen 

concentration, and CO concentration (for gaseous fuels) or smoke-spot number2

 (for 

liquid fuels), and observe flame conditions after unit operation stabilizes at the 

selected firing rate. If the excess oxygen in the stack-gas is at the lower range of 

typical minimum values3

, and if CO emissions are low and there is no smoke, the unit 

is probably operating at near optimum efficiency - at this particular firing rate. 

However, complete the remaining portion of this procedure to determine whether still 

lower oxygen levels are practical. 

602.3 Increase combustion air flow until the stack-gas oxygen levels increase by one or two 

percent over the level measured in Section 602.2. As in Section 602.2, record the 

stack-gas temperature, CO concentration (for gaseous fuels) or smoke-spot number 

(for liquid fuels), and observe flame conditions for these higher oxygen levels after 

unit operation stabilizes. 

602.4 Decrease combustion air flow until the stack-gas oxygen is at the level measured in 

Section 602.2. From this level gradually reduce the combustion air flow, in small 

increments. After each increment, record the stack-gas temperature, oxygen 

concentration, CO concentration (for gaseous fuels), and smoke-spot number (for 

liquid fuels). Also, observe the flame and record any changes in its condition. 

602.5 Continue to reduce combustion air flow stepwise, until one of the following limits is 

reached: 

a. Unacceptable flame conditions - such as flame impingement on furnace walls or 

burner parts, excessive flame carryover, or flame instability; 

1

 THIS TUNING PROCEDURE IS BASED ON A PROCEDURE DEVELOPED BY KVB, INC. FOR THE U.S. EPA. 

2

 THE SMOKE-SPOT NUMBER CAN BE DETERMINED WITH ASTM TEST METHOD D-2156 OR WITH THE BACHARACH METHOD.

THE BACHARACH METHOD IS INCLUDED IN A TUNE-UP KIT THAT CAN BE PURCHASED FROM THE BACHARACH COMPANY. 

3

 TYPICAL MINIMUM OXYGEN LEVELS FOR UNITS AT HIGH FIRING RATES ARE: 

A. FOR NATURAL GAS: 0.5 - 3% 

B. FOR LIQUID FUELS: 2 - 4%. 
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Placer County APCD 231 - 9 Rules and Regulations

b. Stack-gas CO concentrations greater than 400 ppm; 

c. Smoking at stack; 

d. Equipment-related limitations - such as low windbox/furnace pressure differential, 

built-in air-flow limits, etc. 

602.6 Develop an O2/CO curve (for gaseous fuels) or O2/smoke curve (for liquid fuels) 

similar to those shown in Figures 1 and 2 using the excess oxygen and CO or 

smoke-spot number data obtained at each combustion air flow setting. 

602.7 From the curves prepared in Section 602.6, find the stack-gas oxygen levels where 

the CO emissions or smoke-spot number equal the following values: 

Fuel Measurement Value 

Gaseous CO Emissions 400 PPM 

#1 & #2 Oils Smoke Spot Number Number 1 

#4 Oil Smoke Spot Number Number 2 

#5 Oil Smoke Spot Number Number 3 

Other Oils Smoke Spot Number Number 4 

The above conditions are referred to as the CO or smoke-spot thresholds, or as the 

minimum excess oxygen levels. Compare this minimum value of excess oxygen to 

the expected value provided by the combustion unit manufacturer. If the minimum 

level found is substantially higher than the value provided by the manufacturer, 

burner adjustments can probably be made to improve fuel and air mix, thereby 

allowing operations with less air. 

602.8 Add 0.5 to 2.0 percent to the minimum excess oxygen level found in Section 602.7 

and reset burner controls to operate automatically at this higher stack-gas oxygen 

level. This margin above the minimum oxygen level accounts for fuel variations, 

variations in atmospheric conditions, load changes, and non-repeatability or play in 

automatic controls. 

602.9 If the load of the combustion unit varies significantly during normal operation, repeat 

Sections 602.1-602.8 for the firing rates that represent the upper and lower limits of 

the range of the load. Because control adjustments at one firing rate may affect 

conditions at other firing rates, it may not be possible to establish the optimum 

excess oxygen level at all firing rates. If this is the case, choose the burner control 

settings that give the best performance over the range of the firing rates. If one firing 

rate predominates, the setting should optimize the conditions at the rate. 

602.10 Verify that the new settings can accommodate the sudden load changes that may 

occur in daily operation without adverse effects. Do this by increasing and 

decreasing load rapidly while observing the flame and stack. If any of the conditions 

in Section 602.5 result, reset the combustion controls to provide a slightly higher level 

of excess oxygen at the affected firing rates. Next, verify these new settings in a 

similar fashion. Then make sure that the final control settings are recorded at steadystate operating conditions for future reference. 
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Rules and Regulations 231 - 10 Placer County APCD 

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Figure 1

Oxygen(O2)/CO Characteristic Curve

SOURCE: KVB INC.

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Placer County APCD 231 - 11 Rules and Regulations
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Rules and Regulations 231 - 12 Placer County APCD 
Figure 2

Oxygen(O2)/Smoke Characteristic Curve SOURCE: KVB INC.

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Placer County APCD 231 - 13 Rules and Regulations
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Rules and Regulations 231 - 14 Placer County APCD