Rule Criteria Processing

It is important to understand how the FEMS Smart System uses the rule criteria entered on the Rule Definition form in order to achieve the maximum benefits provided by the system for an efficient leak detection and repair program at your enterprise.

For instruction on rule criteria processing for the FEMS Smart System, click the following links or use the scroll bar to scan the page.

Frequency Conversions

The FEMS Smart System supports only the default frequencies shipped with the software. An (SS) designation identifies each Smart System frequency. The Smart System is designed to "honor" a Tag's current monitoring and visual inspection frequency settings by converting each to an equivalent Smart System-defined frequency. The conversion occurs during the first execution of the Smart System for an entity and each time a new regulation is assigned to a Tag. This feature can be useful when Tag monitoring frequencies have been managed external to Sphera Essential.

In order to convert a Tag's current monitoring or visual inspection frequency to a Smart System-defined frequency, a Time Basis and Frequency Definition must be set for each frequency used (e.g., Monthly, Quarterly, Q1, Q2, etc.) and must match the Time Basis and Frequency Definition of a Smart System frequency. Otherwise, no conversion will take place.

The appropriate Time Basis and Frequency Definition settings for some of the more common frequencies are described below.

Monitoring Periods

A weekly monitoring period runs from Sunday through Saturday. A monthly monitoring period starts on the first day of the month and ends on the last day of the month. A month is the basis for all other frequencies. For example, a quarterly monitoring period begins on the first day of the first month of the quarter and ends on the last day of the third month of the quarter.

The FEMS Smart System reviews performance data during partial as well as full monitoring periods to identify leaking components. However, when evaluating for frequency changes, only full and complete monitoring periods are considered.

Calendar- and Skip Period-Based Approach for Monitoring Periods

The FEMS Smart System uses the calendar- or skip period-based approach when determining monitoring periods for evaluating performance against rule criteria and setting frequency change dates. The calendar-based approach follows standard calendar year time periods, such as annual, January 1 - December 31, first quarter, January 1 - March 31, second quarter, April 1 -June 30, etc. The skip period-based approach allows non-standard time periods to be used, such as annual, June 1 - May 31, first quarter, June 1 - August 31, second quarter, September 1 - November 30, etc.

There is no difference between calendar- and skip period-based approaches for weekly and monthly frequencies. A weekly monitoring period runs from Sunday through Saturday. A monthly monitoring period starts on the first day of the month and ends on the last day of the month.  

For the skip period-based approach, a quarter (3 calendar months) is the common denominator for all other frequencies. The first quarter begins the first day of the month following the month during which the last monitoring event occurred. The quarters for the skip period-based approach when the monitoring took place in January 2004 are:

To maintain this skip period-based schedule, the next monitoring event must occur during the 3rd month of a quarter. For example, if the frequency is Quarterly, the next monitoring event must take place in April 2004. If the frequency is semiannually, the next monitoring event must occur in July 2004.

Using the example above (i.e., monitoring event in January 2004, skip period quarters identified), the skip period-based approach for determining monitoring periods for each of the default frequencies is described below.

• Quarterly - The initial period begins on the first day of the month following the monitoring event, February 1, 2004. The end date of the initial period is April 30, 2004 and the start date of the next period is May 1, 2004. Monitoring should take place during the 3rd month of each quarter, April 2004, July 2004, October 2004 and January 2005.

• Semiannually - The system skips one quarter (three months) to determine the end date of the initial period, July 31, 2004 and the start date of the next period, August 1, 2004. The next monitoring event should take place in July 2004, the 3rd month of the quarter and six months after the January 2004 monitoring event.

• Annually - The system skips three quarters (nine months) to determine the end date of the initial period, October 31, 2004 and the start date of the next period, November 1, 2004. The next monitoring event should take place in January 2005, the 3rd month of the quarter and twelve months after the January 2004 monitoring event.

• Biannually - The system skips seven quarters (twenty-one months) to determine the end date of the initial period, October 31, 2005 and the start date of the next period, November 1, 2005. The next monitoring event should take place in January 2006, the 3rd month of the quarter and twenty-four months after the January 2004 monitoring event.

• Once Every 4 Years - The system skips fifteen quarters (forty-five months) to determine the end date of the initial period, October 31, 2007 and the start date of the next period, November 1, 2007. The next monitoring event should take place in January 2008, the 3rd month of the quarter and forty-eight months after the January 2004 monitoring event.

• Once Every 8 Years - The system skips thirty-one quarters (ninety-three months) to determine the end date of the initial period, October 31, 2011 and the start date of the next period, November 1, 2011. The next monitoring event should take place in January 2012, the 3rd month of the quarter and ninety-six months after the January 2004 monitoring event.

To change the starting month for the quarters used in the skip period-based approach, perform your monitoring during the month before the month the first quarter should begin.

Frequency Changes

Each time the FEMS Smart System changes the monitoring frequency for a component (or component group), it stores the date of the change. The date stored is the end date of the monitoring period during which the component (or component group) qualified for the change, e.g., Saturday for weekly frequencies and the last day of the month for all other frequencies. When a frequency changes, the "first available next monitoring period" is used as the starting point for evaluation at the new frequency. Three different examples are provided below:

1. The system is evaluating a component (or component group) for the month of March 2004. If the current frequency is Monthly and the component qualifies for a change to a quarterly frequency during March, the change date is set to March 31, 2004 and the new monitoring period begins on April 1, 2004, the next available monitoring period at the new frequency.

2. The system is evaluating a component (or component group) for the month of July, 2004. If the current frequency is Monthly and the component qualifies for a change to a quarterly frequency during July, the change date is set to July 31, 2004. If the calendar-based approach is being used, the new monitoring period begins on September 1, 2004, the next available monitoring period for a calendar-based quarter. When the skip period-based approach applies, the new monitoring period begins on August 1, 2004, the next available monitoring period for the skip period-based approach. For more information about calendar- and skip period-based approaches, refer to Calendar- and Skip Period-Based Approach for Monitoring Periods.

3. The system is evaluating a component (or component group) for the weekly monitoring period of March 9 - 15, 2004 and the component qualifies for a change to a monthly frequency. The change date is set to March 15, 2004 (Saturday) and the new monitoring period begins on April 1, 2004, the next available monitoring period at the new frequency.

Since the FEMS Smart System also reviews performance data during partial periods, the component in example C above would be checked for leaks during the partial period of March 16 - 31, 2004. (If the component leaks, leak criteria specified for the rule definition is applied.)

When a component's frequency changes before all of the available monitoring periods have been evaluated for the component during a single FEMS Smart System run, the system evaluates the remaining monitoring periods using the criteria established for the new frequency. For example, assume it is June 1, 2004 and the FEMS Smart System is running. In example C above, the component would also be evaluated with the criteria defined for the monthly frequency in April 2004 and May 2004 during the same FEMS Smart System run.

Consecutive Periods for Frequency Changes

Consecutive periods represent the number of successive periods a component must be a non-leaker to change frequencies and advance to another frequency level. Likewise, for component groups, the percentage of the components that are leaking must be at or below the specified leak percentage value for the number of consecutive periods defined in order to change frequencies. The FEMS Smart System uses the current frequency (At Frequency) to determine consecutive periods. For example, if the current frequency is Monthly, one consecutive period is equal to one month; if the current frequency is Quarterly, one consecutive period is equal to three months.

Rule Types

Rule types indicate whether a regulation is component- or aggregate-based.

• Component - The performance of each component is checked individually to determine its monitoring frequency.

• Aggregate - The performance of a group of components is checked and a percentage of the components that are leaking is used to determine the monitoring frequency.

Component-Based Rule Type

The number of consecutive periods required to change the frequency level from Weekly to Monthly, Monthly to Quarterly, etc. when the component's performance matches the ppm defined for the rule definition are specified for component-based rule criteria. One instance of the following values defines component-based rule criteria:

• At Frequency (current frequency)

• Number of Consecutive Periods

• New Frequency

Just one rule criteria instance can exist for each frequency defined as the current frequency. For example, once rule criteria is established for the current frequency Monthly, no other rule criteria can be defined with a current frequency of Monthly.

Maintenance Frequency Level for Component-Based Rule Criteria

A maintenance frequency level must be defined for the strictest frequency, where the current and new frequencies are equal to the strictest frequency for one consecutive period. The maintenance frequency level ensures the system will continue to apply the strictest frequency when the component's performance continues to qualify it for monitoring at the strictest frequency. If a maintenance frequency level does not exist, the initial frequency level will be applied. For example, assume the strictest frequency for a regulation is Annually and the criteria for this frequency has been defined as:

• At Frequency = Semiannually

• Consecutive Periods = 2

• New Frequency = Annually

The maintenance frequency level for this example would be defined as:

• At Frequency = Annually

• Consecutive Periods = 1

• New Frequency = Annually

If the maintenance frequency level did not exist, there would be no criteria for the system to use to evaluate the component at its current frequency, Annually. With the maintenance frequency level defined, the system can determine if the component continues to qualify for monitoring at the strictest frequency. The FEMS Smart System applies the initial frequency when no maintenance frequency criteria has been defined.

Post-Repair Frequency Levels

After a component leaks and has been repaired, the initial frequency can be applied to the component or multiple levels of frequency based on ppm readings can be defined. The ppm reading triggers the frequency setting when multiple frequency levels have been defined. For example, a frequency level can be specified to set the monitoring frequency to Monthly when the component's ppm reading is 1000 at a Weekly frequency. Another level might be defined for a ppm reading of 1000 where the beginning frequency level is Quarterly and the new frequency setting is Monthly. Still another level might be defined for a ppm reading of 500 where the beginning frequency level is Semiannually and the new frequency is Quarterly.

Aggregate-Based Rule Type

The component grouping basis, frequency levels, performance percentage that triggers a frequency change, number of consecutive periods, and calculation method define aggregate-based rule criteria. Repair delay credits, removed component credits, components monitored, and same frequency monitoring period for leak percentage calculations can be applied to further define aggregate-based rule criteria.

Grouping Basis

The grouping basis (areas, subareas, process units) setting for aggregate-based rule criteria is combined with the regulation name, effective date, equipment category, equipment type and chemical state defined for the rule definition to determine the component group for calculating leak percentages. It is recommended that no edits be made to this setting once the rule definition has been used by the FEMS Smart System. Changing the grouping basis is the equivalent of setting up a new component group; the frequency history accumulated for the group is invalidated, the monitoring frequency is reset, and rule evaluation starts over.

Frequency Levels

Successive or non-successive frequency levels for aggregate-based rule criteria can be defined. Successive levels allow movement to sequential frequencies only. Non-successive levels allow movement to other frequencies based on performance. Review the following examples:

• Successive Levels Example

• Non-Successive Levels Example

Using the examples above, if monitoring is occurring on a weekly basis, the percentage of leakers is 1%, and successive levels have been defined, the frequency level would be changed to Monthly, the next sequential frequency. When using the non-successive level definitions, the frequency would be changed to Annually.

Maintenance Frequency Level for Aggregate-Based Rule Criteria

A maintenance frequency level must be defined for the strictest frequency, where for one consecutive period, the current and new frequencies are equal to the strictest frequency and leak percentage that triggers the frequency change matches the one for the strictest frequency. The maintenance frequency level ensures the system will continue to apply the strictest frequency when the component group's performance continues to qualify for monitoring at the strictest frequency. If a maintenance frequency level does not exist, the initial frequency level will be applied. For example, assume the strictest frequency for a regulation is Annually and the criteria for this frequency has been defined as:

• At Frequency = Semiannually

• Trigger % = 3

• Consecutive Periods = 2

• New Frequency = Annually

The maintenance frequency level for this example would be defined as:

• At Frequency = Annually

• Trigger % = 3

• Consecutive Periods = 1

• New Frequency = Annually

If the maintenance frequency level did not exist, there would be no criteria for the system to use to evaluate the component group at its current frequency, Annually. With the maintenance frequency level defined, the system can determine if the component group continues to qualify for monitoring at the strictest frequency. The FEMS Smart System applies the initial frequency when no maintenance frequency criteria has been defined.

Leak Percentage Calculation

A percentage of the components that are leaking is used to determine the monitoring frequency for aggregate-based regulations. Leak percentage calculations can be based on the total components in service in the group or just the total components in the group that were monitored. Any repair delay credits and removed component credits are applied when the leak percentage for a component group is calculated. The Leak Percentage Calculation used by the FEMS Smart System is shown below.

Calculation Methods

The calculation methods used for aggregate-based rule criteria are:

• Consecutive Periods Calculation - The leak percentage is calculated for the number of consecutive monitoring periods defined for the rule criteria.

• Rolling Average Calculation - The leak percentage average for the number of rolling periods specified is calculated for the number of consecutive monitoring periods defined for the rule criteria. When there is more than one consecutive period, the leak percentage for each period is combined and averaged to determine the rolling average calculation. For additional calculation information, refer to Rolling Average Calculation Example.

• Subset Average Calculation - The leak percentage average for the best X periods out of Y periods specified is calculated for the number of consecutive monitoring periods defined for the rule criteria. When there is more than one consecutive period, the leak percentage for each period is combined and averaged to determine the subset average calculation. For additional calculation information, refer to Subset Average Calculation Example.

Required Monitoring Periods

For both averaging calculation methods, a required number of monitoring periods must exist before the FEMS Smart System will evaluate the rule criteria for the component group. The following equation is used to determine the number of required monitoring periods:

(Consecutive Periods + Rolling/Subset Average Calculation Periods) - 1 = Required Periods

The Y value is used for the Subset Average Calculation Periods.

Monitoring Periods of the Same Frequency

Both averaging calculation methods use monitoring periods of different frequencies, e.g., Monthly, Quarterly, Annually, etc., in the calculation. When the "Periods must be of the same frequency for leak calculations" option has been selected, the calculation will be deferred until the number of monitoring periods specified are of the same frequency and the required number of monitoring periods exist. Other rule criteria will continue to be evaluated during the time a calculation is deferred. Using the "Periods must be of the same frequency for leak calculations" option is the equivalent of applying the strictest interpretation of the regulation.

Note:  The "Periods must be of the same frequency for leak calculations" option applies to monitoring periods only. The FEMS Smart System determines consecutive periods based on the current frequency (At Frequency).

Rolling Average Calculation Example

The rule criteria used for an example rolling average calculation method is described below.

• Current Frequency = Monthly

• Rolling Average Periods = 3

• Consecutive Periods = 2

• Required Periods = 4 [(3 + 2) - 1 = 4]

• Frequency Change Date = December 31st

• Monitoring Periods:

Assume the FEMS Smart System is running on June 1st. The rolling average periods and consecutive periods have been specified. The system has determined the required monitoring periods exist and has defined the monitoring periods based on the current frequency, the change date, and the current FEMS Smart System run date.

For the first and most recent consecutive period (period 5), the system starts with the most recent monitoring period, May, and calculates the leak percentage. Next, the system calculates the leak percentage for April and March to satisfy the three rolling average periods requirement. The system averages the leak percentages for May, April, and March to calculate the leak percentage for the first consecutive period.

For the second consecutive period (period 4), the system starts with the next descending monitoring period, April, and calculates the leak percentage. Next, the system calculates the leak percentage for March and February to satisfy the three rolling average periods requirement. The system averages the leak percentages for April, March, and February to calculate the leak percentage for the second consecutive period.

Subset Average Calculation Example

The rule criteria used for an example subset average calculation method is described below.

• Current Frequency = Monthly

• Average Best 3 of 4 Periods

• Consecutive Periods = 2

• Required Periods = 5 [(4 + 2) - 1 = 5]

• Frequency Change Date = December 31st

• Monitoring Periods:

Assume the FEMS Smart System is running on July 1st. The rule criteria specifies the best 3 out of 4 periods for 2 consecutive periods. The system has determined the required monitoring periods exist and has defined the monitoring periods based on the current frequency, the change date, and the current FEMS Smart System run date.

For the first and most recent consecutive period (period 6), the system starts with the most recent monitoring period, June, and calculates the leak percentage. Next, the system calculates the leak percentage for May, April, and March to satisfy the best out of four periods requirement. The system combines and averages the best three leak percentages from the June, May, April, and March results to calculate the leak percentage for the first consecutive period.

For the second consecutive period (period 5), the system starts with the next descending monitoring period, May, and calculates the leak percentage. Next, the system calculates the leak percentage for April, March, and February to satisfy the best out of four periods requirement. The system combines and averages the best three leak percentages from the May, April, March, and February results to calculate the leak percentage for the second consecutive period.

Repair Delay Credits

A credit for a component with a repair delay status in the current monitoring period that was identified as non-repairable in a prior monitoring period may be applied during the current monitoring period depending on the reason for the non-repairable status, and provided repair delay credits are allowed by the regulation. Valid repair delay reasons for repair delay credits are:

• Excessive Emissions

• Repair Infeasible w/o Shutdown

• Repair Requires New Design

Any components initially identified as non-repairable in the current monitoring period cannot be credited.

Typically, a maximum number of credits can be applied during one monitoring period. The FEMS Smart System subtracts the number of credits, up to the maximum specified, from the number of leakers when calculating the leak percentage for aggregate-based rule criteria.

Removed Component Credits

A credit for the components removed from a component group may be applied when allowed by the regulation. The FEMS Smart System subtracts the number of components added during a monitoring period from the total number of components removed and multiplies that result by the removed component credit multiplier. The credit is added to the component group when calculating the leak percentage for aggregate-based rule criteria.  

FEMS Smart System Processing for Component-Based Rule Criteria

The FEMS Smart System uses the process described below when a component is evaluated for component-based rule criteria.

1. The system retrieves the current frequency setting for the component and the change date for the frequency to determine the monitoring periods available since the change date.

2. When a complete monitoring period exists, the system evaluates the component for a leak during each monitoring period. Regardless of the number of times the component was monitored during a period, if it registers a leak for any monitoring event, it is flagged as a leaker.

3. For leakers, the system determines if the component's frequency should be changed to the initial frequency or if the component's ppm reading should be evaluated with the leak criteria frequency levels specified.
   
   For non-leakers, the system determines if the number of non-leaking monitoring periods matches the number of consecutive periods specified. If the consecutive periods requirement has not been met, no frequency change is made.

4. If a new frequency is applicable, the system sets the frequency change date to the last day of the monitoring period during which the component became eligible for a frequency change. The beginning of the next monitoring period is the first available monitoring period after the frequency change date.

5. The system assigns the new frequency to the component. Frequencies can be viewed in the Compliance section on the Tag form.  

6. If additional monitoring periods exist after the frequency change date, the system evaluates the component at the new frequency.

FEMS Smart System Processing for Aggregate-Based Rule Criteria

When the FEMS Smart system selects a component for aggregate-based rule criteria evaluation, it determines the component's group and the group's evaluation status for the current run. If the group has been evaluated, the system assigns the group's frequency to the component. When the group has not been evaluated for aggregate-based rule criteria, the system uses the process described below.

1. The system retrieves the current frequency and change date for the frequency to determine the monitoring periods available since the change date.

2. When a full and complete monitoring period exists and required monitoring periods criteria has been met, the system evaluates every component in the group for a leak during each monitoring period. Regardless of the number of times the component was monitored during a period, if it registers a leak for any monitoring event, it is flagged as a leaker.

3. For each monitoring period, the system calculates the leak percentage using the Leak Percentage Calculation.

4. For the current frequency level with the lowest leak percentage that triggers a frequency change, the system applies the specified calculation method, consecutive, rolling average, or subset average, and compares the calculation results with the trigger.
   
   If the component group does not meet the criteria for the current frequency level with the lowest trigger, the system performs the same evaluation using the criteria for the current frequency level with the next highest trigger, and continues in ascending order. The evaluation stops when the component group meets frequency level criteria. When there is no match, no frequency change is made.

5. If a new frequency is applicable, the system sets the frequency change date to the last day of the monitoring period during which the component group became eligible for a frequency change. The beginning of the next monitoring period is the first available monitoring period after the frequency change date.

6. The system assigns the new frequency to each component in the group. Frequencies can be viewed in the Compliance section on the Tag form.  

7. If additional monitoring periods exist after the frequency change date, the system evaluates the component at the new frequency.

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