UNlTEDSTATESENVlRONMENTALPROTECTlONAGENCY Office ofAirQuality Planning andStandards Research Triangle Park,North Carolina 27711



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MEMORANDUM SUBJECT: Performance Test Calculation FROM: William G. Laxton, Director

Technical Support Division, -wf A, ' '- 

### John S. Seitz, Director Stationary Source Compliant TO: NewSource Performance Standards/National Emission

Standards for Hazardous Pollutants Compliance Contacts

Thefollowing guidelines should be used in calculating and reporting emission rates and concentrations when determining compliance with the new source performance standards (NSPS) and national emission standards for hazardous pollutants (NESHAP). These guidelines can also be used for State implementation plans (SIP's). The areas addressed in this memorandum concern metric and English measurement systems, significant figures (SF's) in the emission standards, SF's to carry in intermediate calculations, and the rounding of final emission value numbers to the proper SF's. 

### 1. Use only the emission standard in the metric units to determine compliance. \

The policy of using the metric system wasestablished back in 

### the early * 1970's. Whenthe Environmental Protection Agency (EPA) proposed standards for seven source categories (38 FR15406) onJune 

### 11, 1973, EPAstated: "The Environmental Protection Agency has adopted apolicy of expressing standards in the metric rather than English system. Although technical terms in test methods 

### 10and 

### 11are expressed in metric units, many of those in test methods 

### 1through 9are expressed in English units. Test results derived through calculations in test methods 

### 1through 9must be converted to metric units to agree with the form of the proposed standards." In keeping with this policy, EPApromulgated amendments to Subparts D, E, F, G, and

### tlon

### June 14, 1974 (39 FR20790). In the preamble of this rulemaking, EPAstated: ,I

....Also; to be consistent with the Administrator's policy of converting to the metric system, the standards of performance and other numerical entries, which were originalJy expressed in English2

. .

, .-; r$f units, are converted to metric units. Someof the numerical entries are

rounded after conversion to metric units. It should be noted that the methods in the appendix will be changed to metric units at alater date." The change to metric units for the test methods were proposed on 

## June8, 1976 (41 FR23060) and promulgated onAugust 18, 1977 (42 FR41754). Clearly, EPA's intent wasto use the metric units to determine compliance. However, onapractical scale, the use of the metric or the English system of units would not make any difference in determining whether asource is in compliance or out-of-compliance. Only in very rare cases will separate calculations in the metric and in the English systems with the samesource test measurement values result in one system showing compliance while the other does not. Therefore, it is not necessary to reouire source testing firms to submit the results in the metric units on aroutine basis. 

## It is suggested that if the value in English units is within 1percent of the emission standard and if such adifference is'of concern in your enforcement strategy, then the value should be converted to metric to determine compliance. The numerical value in English units (in parentheses) are to be considered asclose approximations of the metric and should not be used to determine compliance in borderline cases. 2. Consider all emission standards to have at least two SF’s, but no more than three SF's. Asareview, anSFis any digit that is necessary to define the specific value or quantity. Zeros maybe used either to indicate aspecific value, like any other digit, or to indicate the magnitude of anumber. Examples are given below:

Ex. 

## 1: 1300 or 1.3 xlo3 Ex. 2: hgs two SF's.

1300. or 1.300 x10 asfour SF's. Ex. 3: 1300.0 or 1.3000 x Ex. 4: 13040 or 1.304 x

## 1 4 4 09has five SF's. hasfour SF's. Ex. 5: 0.034 or 3.4 x

## lo- ha2 two SF's. Ex. 6: 0.03400 or 3.40 Ex. 7: 0.03 or 3xlo-!Ix10 has four SF's. has one SF. Because the emission standards were not written with consideration to the rules of SF's, especially with the use of zeros, all existing emission standards are considered to have at least two SF's, but nomore than three SF's, under this guideline., Thus:

Case 1: 9dmg/dscm (Subpart I) is considered to be 90. (two SF's). Case 2: 520 rig/J (Subpart Da) is considered to be 520. (three-SF's). Case3: 0.05 kg/Mg (Subpart S) is considered to be 0.050 (two SF's). Case 4: 0.1 g/kg (Subpart BB) is considered to be 0.10 (two SF's).

...-.._-.“----..._. _ ___ _._.“. ^.“”

.3 Case 5: 0.005 g/kg (Subpart BB) is considered to be0.0050

(two SF's). Case 6: 3870 kg/28 days (Subpart BBB) is considered

to have (three SF's). The above rule differs from the previous guidance given by the predecessor of the Stationary Source Compliance Division. 

### In his August 20, 1980 memorandum to Ms. Louise 

### Jacobs, Director of Enforcement Division of Region VII, Mr. Edward E. Reich, Director of the Division of Stationary Source Enforcement interpreted the emission standards asbeing absolute, i.e., ashaving an infinite number of SF's. Using the example of an emission standard of 0.04 gr/dscf, Mr. Reich wrote: "As alegal matter, anything greater than 0.04 is aviolation (e.g., 0.0401). However, since the third digit was not established, most engineers in reporting results would tend to round off and therefore 0.044 would be reported as0.04 and 0.045 would be reported as0.05. Abetter guide would be that anything showing greater than aten percent excess is worth considering for enforcement action." Although the newguidance appears to beamajor shift in Agency policy, it is not, because only very limited cases, if any, would be involved. For example, if the emission standard is 90mg/dscm, 90.0000001 mg/dscm would be in violation according to the August 20, 1980 guidance. However, such an occurrence would be highly unlikely. (Note also that strict adherence to an infinite number of SF's would require an infinite number of SF's in conversion factors, which is apractice that is impossible to follow.) Therefore, the effect of the change to two or three SF's in the emission standards would be practically nodifferent from the initial guidance. 

### 3. Carry at least five significant digits in intermediate calculations. a Since the measurement of variables and sample quantities during source performance tests are recorded in metric or English units or acombination of - both, specifying specific rules to handle SF's in addition, subtraction, multiplication, and division would become cumbersome. Tokeep things on a practical basis for emission standards with two or three SF's, English or metric maybeused provided that at least five SF's are retained (most calculators retain nine digits) in a17 intermediate calculations. The final calculation after averaging all the runs should produce the metric units, if necessary. Then the final number should be rounded off asdescribed below to determine compliance. 

### 4. Roundoff calculated emission nu&ers to the number of SF’s determined bythe rule stated in (2) above. Whenrounding off afigure, the following procedure, based on practices given under the American Society for Testing and Materials (ASTM) (Standard for Metric Practice E380), should be used: 

### If the first digit to be discarded is less than five, the last digit retained should not be changed. Whenthe first digit discarded is greater than five, or if it is afive1

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### 4

followed by at least one digit other than 0, the last figure retained should be increased by one unit. Whenthe first digit discarded is exactly five, followed only byzeros, the last digit retained should be rounded upward if it is anodd number, but noadjustment made if it is aneven number. For example, if the emission standard is 90, then 90.357 would be rounded to 90, 90.639 would be rounded to 91, 90.500 would be rounded to 90, and 91.500 would be rounded to 92. '. Consideration wasgiven to round upward when the last digit to be discarded is five; however, because the occurrence of the first digit to be discarded being exactly five followed byzeros is rare, it wasdecided to be consistent with the ASTMpractice.

cc: 

### JackR. Farmer, ESD(MD-13) John Calcagni, AQMD(MD-15) 

### J.E. McCarley, EMB(MD-14) Rodney M. Midgett, QAD(MD-77A) Louis R. Paley, SSCD

### (EN-341) RonShafer, SSCD(EN-341) Roger T. Shigehara, EMB(MD-19) 

### JohnJ.Silvasi, AQMD

### (MD-15) Gilbert H. Wood, EMB(MD-14) Susan R. Wyatt, CPB

### (MD-13)

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