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VENTURA COUNTY AIR POLLUTION CONTROL DISTRICT 

RULE 74.9 - STATIONARY INTERNAL COMBUSTION ENGINES 

(Adopted 7/21/81, Revised 7/2/85, 9/5/89, 12/3/91, 12/21/93, 11/14/00, 11/8/05) 

A. Applicability 

 This rule applies to any stationary spark-ignited or diesel internal combustion engine rated at 

50 or more horsepower, operated on any gaseous fuel, including liquid petroleum gas (LPG), 

or liquid fuel, and not subject to the provisions of Rule 74.16. 

B. Requirements 

 1. Except as noted in Subsection B.1.a, the owner or operator of a stationary internal 

combustion engine to which this rule is applicable shall limit emissions from that 

engine to no more than the following: 

 Engine Type NOx ROC CO 

 (ppmv) (ppmv) (ppmv) 

 Rich-burn, general 25 250 4500 

 Lean-burn, general 45 750 4500 

 Diesel 80 750 4500 

 Rich-burn, waste gas 50 250 4500 

 Lean-burn, waste gas 125 750 4500 

 where ppmv = parts per million by volume at 15 percent oxygen on a dry basis 

 NOx = oxides of nitrogen 

 ROC = reactive organic compounds 

 CO = carbon monoxide 

 a. Carbon monoxide emissions from any engine installed after November 8, 

2005, shall be limited to 2000 ppm by volume at 15 percent oxygen on a dry 

basis. 

 2. In lieu of compliance with a NOx emission limit in Subsection B.1, engines may 

achieve and maintain a percent NOx reduction by weight limit specified below, as 

measured concurrently across an emission control device: 

 Rich-burn, general 96 percent 

 Lean-burn, general 94 percent 

 Diesel 90 percent 

 

 3. No person shall allow the discharge into the atmosphere of ammonia (NH3) in excess 

of 20 ppmv from any emission control device installed and operated pursuant to the 

requirements of Subsections B.1 or B.2 above. 
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4. The owner or operator of a stationary internal combustion engine shall perform a 

biennial source test to verify compliance with all applicable emission limits. A 

source test shall consist of the average of three (3) runs, with data from each run 

averaged over 15 consecutive minutes. 

5. The owner or operator of a stationary internal combustion engine shall perform a 

screening analysis of NOx and CO emissions on a quarterly basis unless: 

a. the biennial source test specified in Subsection B.4 is required, or 

b. the engine operated less than 32 hours in each of the three months of the 

applicable quarter, as measured by a non-resettable elapsed operating hour 

meter. 

The operator shall notify the APCD by telephone 24 hours prior to any quarterly 

screening analysis. 

C. Engine Operator Inspection Plan 

 The operator of an engine subject to the provisions of Subsection B.1 or B.2 of this rule shall 

submit to the District an Engine Operator Inspection Plan for review and approval by the Air 

Pollution Control Officer in writing. The plan shall be updated after any change in 

operation. For new engines and modifications to existing engines, issuance of the Permit to 

Operate shall be contingent on approval of the plan. The operator may request a change to 

the plan at any time. 

 The Plan shall include the following: 

 1. The manufacturer, model number, rated horsepower, and combustion method (i.e., 

rich-burn, lean-burn or diesel) of the engine. 

 2. A description of the NOx control system installed on the engine (if any), including 

type (e.g., nonselective catalyst, "clean-burn" combustion) and manufacturer, as well 

as a description of any ancillary equipment related to the control of emissions (e.g., 

automatic air/fuel ratio controller, fuel valves). 

 3. The company identification number and the location of the engine by a schematic of 

the affected facilities. 

 4. A specific emission inspection procedure to assure that the engine is operated in 

continual compliance with the provisions of this rule. The procedure shall include an 

inspection schedule. At a minimum, inspections shall be conducted quarterly unless 

the engine operated less than 32 hours in each of the three months of the applicable 

quarter, as measured by a non-resettable elapsed operating hour meter. 

 5. Each preventative or corrective maintenance procedure or practice that will be used 

to maintain the engine and NOx control system in continual compliance with the 
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provisions of this rule, including the response time for both corrective action and 

reinspection. 

D. Exemptions 

 The provisions of Sections B, C and E of this rule shall not apply to the operation of 

stationary internal combustion engines used under the following conditions: 

 1. Engines rated at less than 50 brake horsepower. 

 2. Engines operated less than 200 hours per calendar year. Engines claiming this 

exemption shall be required to install and operate a non-resettable elapsed operating 

hour meter. 

 3. Emergency standby engines operated during either an emergency or maintenance 

operation. Maintenance operation is limited to 50 hours per calendar year. Engines 

claiming this exemption shall be required to install and operate a non-resettable 

elapsed operating hour meter. 

 4. Engines used in research or teaching programs. 

 5. Engines used directly and exclusively for agricultural operations necessary for the 

growing of crops or the raising of fowl or animals. 

 6. Engine test stands used for evaluating engine performance. 

 7. All engines rated at less than 100 horsepower, emitting NOx at not more than 5 

gm/bhp-hr (shaft), and utilized as a qualified cogeneration facility permanently 

displacing the use of a specified boiler or boilers. This exemption shall apply to only 

those engines installed prior to December 31, 1988. A qualified cogeneration facility 

is one meeting the requirements of 18 CFR Part 292 Subpart B Section 292.205. 

 8. Diesel engines with a permitted capacity factor of 15 percent or less. 

 9. Diesel engines used to power cranes and welding equipment. 

 10. Diesel engines operated on San Nicolas island and Anacapa Island. 

E. Recordkeeping Requirements 

 1. The owner or operator of any engine subject to the provisions of Section B of this 

rule shall maintain an inspection log containing, at a minimum, the following data: 

 a. Identification and location of each engine subject to the provisions of this 

rule, 

 b. Date and results of each screening analysis and inspection, 
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 c. A summary of any emissions corrective maintenance taken, and 

 d. Any additional information required in the Engine Operator Inspection Plan. 

The operator shall maintain the inspection log for a period of 2 years after the date of 

each entry. The log shall be available for inspection by the District upon request. 

2. For each engine exempt from quarterly screening analysis pursuant to Subsection 

B.5.b and inspection pursuant to Subsection C.4, the owner or operator shall record 

total hours of operation each month. Records shall be maintained for a period of 2 

years after the date of each entry. 

F. Reporting Requirements 

 1. Within 45 days of the end date of each permit renewal period, the operator of a 

permitted engine subject to the provisions of this rule shall provide the District with 

the following information: 

 a. Engine manufacturer, model number, operator identification number, and 

location. 

 b. A summary of maintenance reports during the renewal period, including 

quarterly screening data if applicable. 

 2. For each engine exempt pursuant to Subsection D.2, total annual operating hours 

shall be reported annually. For each engine exempt pursuant to Subsection D.3, total 

annual hours of maintenance operation shall be reported annually. Reports shall be 

provided to the District after every calendar year by February 15. 

. 

G. Test Methods 

 1. Oxides of nitrogen emissions for compliance source tests shall be determined by 

using ARB Method 100. 

 2. Carbon monoxide emissions for compliance source tests shall be determined by 

using ARB Method 100. 

 3. Reactive organic compound emissions for compliance source tests shall be 

determined by using EPA Method 25 or EPA Method 18, referenced to methane. 

 4. Oxygen content for compliance source tests shall be determined by using ARB 

Method 100. 

 5. Screening analyses shall be performed using a portable analyzer either verified by the 

Environmental Protection Agency or approved in writing by the APCO. The 
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portable analyzer shall be calibrated, maintained and operated in accordance with the 

recommendations of the manufacturer. 

 6. Ammonia emissions shall be determined using Bay Area Air Quality Management 

District Method ST-1B, dated 1/20/82. 

 7. Non-resettable elapsed operating hour meters shall be maintained in accordance with 

the recommendations of the manufacturer. 

H. Violations 

 1. Failure to comply with any provision of this Rule shall constitute a violation of this 

rule. 

 2. It is the responsibility of the engine operator to demonstrate to the satisfaction of the 

Air Pollution Control Officer that an engine subject to the provisions of this rule is 

being operated in continuous compliance with all applicable provisions of this rule. 

 An engine shall be in violation if it is operated out of compliance with an approved 

Engine Operator Inspection Plan. However, if data from a source test of the engine 

operating under identical conditions indicates that the engine is in compliance with 

the requirements of this rule, then a violation will not have occurred. The source test 

shall be conducted at the engine operator's expense. 

I. Definitions 

 1. "Diesel Engine": A compression ignited two or four-stroke engine in which liquid 

fuel injected into the combustion chamber ignites when the air charge has been 

compressed to a temperature sufficiently high for auto-ignition. 

 2. "Emergency Standby Engine": An internal combustion engine used only as follows: 

 a. When normal power line or natural gas service fails. 

 b. For the emergency pumping of water for either fire protection or flood relief. 

 An emergency standby engine may not be operated to supplement a primary power 

source when the load capacity or rating of the primary power source has been either 

reached or exceeded. 

 3. "Engine Rating": The output of an engine as determined by the engine manufacturer 

and listed on the nameplate of the unit, regardless of any derating. 

 4. "Lean-burn Engine": Any two or four-stroke spark-ignited engine that is not a richburn engine. 
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 5. "Maintenance Operation": The use of an emergency standby engine and fuel system 

during testing, repair and routine maintenance to verify its readiness for emergency 

standby use, or to facilitate the training of personnel on emergency activities. 

 6. "Oxides of Nitrogen": The sum of nitric oxide (NO) and nitrogen dioxide (NO2) in 

flue gas, collectively expressed as nitrogen dioxide. 

 7. "Permitted Capacity Factor": The annual permitted fuel use divided by the 

manufacturers specified maximum hourly fuel consumption times 8760 hours per 

year. 

 8. "Rich-burn Engine": A two or four-stroke spark-ignited engine where the 

manufacturers original recommended operating air/fuel ratio divided by the 

stoichiometric air/fuel ratio is less than or equal to 1.1. 

 9. "Stationary Internal Combustion Engine": Any internal combustion engine of the 

reciprocating type that is operated at a site for more than one year or is attached to a 

foundation. 

 10. "Stoichiometric Air/Fuel Ratio": The chemically correct air/fuel ratio where all fuel 

and all oxygen in the air/fuel mixture will be consumed. 

 11. "Waste Gas": Fuel gas produced at either waste water/sewage treatment facilities or 

landfills containing no more than 25 percent by volume supplemental gas.