Exam Cheat Sheet · Quick Reference

Oklahoma Residential Contractor Plumbing and Natural Gas

Oklahoma · PSI Services Contractor

Verified, not estimated. Every figure below is drawn from the official exam structure we maintain — question counts, passing standard and topic weighting. Practice questions are grounded in the source law with statute citations. We omit any figure we can't verify rather than guess at it.

Total questions

Passing score

75%

Exam time

180 min

Administered by

PSI Services Contractor

Format

Reference materials allowed

Oklahoma State Portion 85 questions

General Plumbing Knowledge and Regulations 8 Q · 9%

Calculate Area and VolumeGeneral Code RequirementsPlumbing DefinitionsNotches and Holes in Structural MembersTest SystemsWater ColumnPipe OffsetsPiping support requirements and spacing by material typeProtection of piping from physical damage, corrosion, and freezingTrenching, bedding, and backfilling requirementsPipe penetrations, waterproofing, and sealing of annular spacesMaterials identification, listing, and third-party certification +7 more

Piping, Valves, and Control Valves 8 Q · 9%

Piping ConnectionsCast Iron PipingCopper Piping and TubingSteel PipingPVC, CPVC, Plastic and PEX PipingValvesBackflow Prevention Devices and AssembliesWater Supply System Design and Pipe SizingPressure Requirements and Pressure-Reducing ValvesPipe Support Spacing and Installation RequirementsPipe Length Calculations and Fitting AllowancesDrainage Pipe Sizing and Slope Requirements +3 more

Fixtures and Equipment 10 Q · 12%

Fixture InstallationInstall Water HeatersRequirements for FixturesShower Compartment and Receptor RequirementsWater Closet and Flushing Device RequirementsFixture Trap Design and SizingBackflow Prevention Devices and ApplicationsTemperature and Pressure Relief Valves for Water HeatersWater Heater Location and Safety RequirementsBoiler Safety Controls and Operating RequirementsGas Appliance Installation and Clearance RequirementsFixture Standards and Material Requirements +4 more

Water Supply 10 Q · 12%

Water Supply and Distribution LinesProtection of Potable Water SupplyBackflowWater supply system pressure requirements and pressure-reducing valvesThermal expansion control and water hammer arrestorsPipe and tubing materials, joints, and connections for water service and distributionValves and shutoff requirements for water service and fixturesWater supply fixture units and pipe sizing methodsNonpotable water systems identification, storage, and distributionWater heater installation, relief valves, and safety requirementsDwelling unit fire sprinkler system water supply and pipe sizingWater service pipe separation from building sewer +7 more

Drains and Sewers 10 Q · 12%

Drain and Sewer PipeBuilding SewersSewer and Drain CleanoutsDFUsDrain and Water PipingDrainage pipe joints and connections by material typeHorizontal drainage piping slope requirementsDrain pipe sizing using fixture unit loads and tablesCleanout installation requirements and clearancesBackwater valvesSumps and sewage ejectorsDWV system testing procedures +7 more

Vents 7 Q · 8%

Vent InstallationWet VentingVent terminals and termination requirementsAir admittance valvesVent pipe sizing and developed lengthIndividual and common ventsCircuit ventingCombination waste and vent systemsWaste stack ventingIsland fixture ventingTrap seal protection and pressure differential limitsVent grades, connections, and drainage of condensate +6 more

Traps, Interceptors, Indirect, and Special Waste 5 Q · 6%

Ejector PumpsIndirect WasteTrapsTrap seal protection methods (primer valves and barrier devices)Prohibited trap typesTrap sizing requirements by fixture typeNumber of fixtures per trap and double-trapping prohibitionGrease interceptors and separatorsBackwater valvesSumps and ejector design requirementsTrap seal depth requirements (minimum and maximum liquid seal)Trap design and material construction standards +2 more

Isometric Analysis 13 Q · 15%

Isometric DrawingsFitting Allowances and Center-to-End CalculationsOffset, Diagonal, Rise, and Run Relationships45-Degree Offset Constants and Pipe Length CalculationsReading and Interpreting Venting System IsometricsEqual Spacing and Pipe Cut ListsParallel Offset CalculationsGrade, Drop, and Elevation in Plan View DiagramsRolling Offsets and True Offset CalculationsJumper Offsets Using 45° and 90° FittingsCombination Offsets (45° and 60° Fittings)Trigonometric Constants for Non-45° Offset Angles +3 more

Fuel Gas 4 Q · 5%

Gas Piping ConduitGeneral Gas Piping and ValvesPiping Supports and HangarsPipe SizingTestingInstallation and Joining Gas PipeThreadsCombustion air requirements and methodsAppliance location and clearances to combustiblesVenting systems and vent typesElectrical bonding of gas piping (CSST and metallic pipe)Appliance connectors and shutoff valves +11 more

Safety 10 Q · 12%

Construction ActivitiesLaddersFall Arrest SystemsPersonal Protective Equipment (PPE) selection, use, and employer responsibilitiesFire protection and prevention programsExcavation hazards and cave-in protective systemsFirst aid, medical services, and emergency responseHousekeeping and site sanitation requirementsHazardous substances and permissible exposure limitsEmployer safety training and accident prevention responsibilitiesGuardrail system specifications and load requirementsSafety net system installation, testing, and inspection +6 more

Key Distinctions

Soil StackvsWaste Pipe

A soil stack conveys sewage containing fecal material, while a waste pipe conveys only liquid sewage that does not contain fecal material.

International Residential Code, Pages 24 and 27

Forced Draft Venting SystemvsInduced Draft Venting System

Forced draft removes flue gases under positive static pressure, while induced draft removes flue gases under nonpositive static vent pressure.

International Residential Code, Page 21 (Section R202 Definitions — Mechanical Draft System)

Center-to-Center (c-c) LengthvsEnd-to-End (e-e) Length

Center-to-center lengths are equal when spacing is equal, but end-to-end lengths differ when different fitting types are used because fitting allowances vary.

Mathematics For Plumbers And Pipefitters, Chapter 1 — Equal Spacing

Atmospheric Vacuum Breaker Critical LevelvsPressure Vacuum Breaker Critical Level

An atmospheric vacuum breaker requires its critical level set not less than 6 inches above the highest downstream piping/flood level rim, while a pressure vacuum breaker requires not less than 12 inches.

IRC 2018, Section P2902.3.2, Page 632

Building DrainvsBuilding Sewer

The building drain is the lowest interior drainage piping extending 30 inches beyond exterior walls, while the building sewer begins at the end of the building drain and conveys discharge to a public sewer or disposal system.

International Residential Code, Page 13

Threaded Pipe Fitting AllowancevsCopper Fitting Allowance (G)

For threaded fittings, the fitting allowance is center-to-face minus thread-in; for copper fittings, the fitting allowance G is center-to-face minus the depth of the solder cup.

Mathematics for Plumbers and Pipefitters, Page 39

Type C SoilvsStable Rock

Type C soil (e.g., submerged or freely seeping soil) is the least stable category and always requires a protective system for trenches 5 feet or more deep, while stable rock requires no protective system.

29 CFR 1926, Subpart P, §1926.652(a)(1) and Appendix A

Personal Fall Arrest System (PFAS)vsGuardrail System

A worker trained only on guardrail systems must be retrained before using a PFAS because the change in fall protection equipment renders prior training obsolete, and a PFAS subjected to impact loading must be removed from service and inspected before reuse.

29 CFR 1926, Subpart M, §1926.503(c)(2)

Emergency Action Plan (≤10 employees)vsEmergency Action Plan (>10 employees)

For employers with 10 or fewer employees the plan may be communicated orally and need not be maintained in writing, while employers with more than 10 employees must keep a written plan at the workplace available for employee review.

29 CFR 1926, §1926.35(e)(3)

45°/60° Combination Offset — Standard Positionvs45°/60° Combination Offset — Alternate Position

In the standard position, rise equals the offset and setback equals 1.414 × offset; in the alternate position, rise equals 1.414 × offset and setback equals the offset.

Mathematics For Plumbers And Pipefitters, Chapter 2 — Combination Offsets

Pipe Sleeve (foundation wall)vsRelieving Arch (foundation wall)

Either method may protect a pipe passing through a foundation wall, but if a sleeve is used it must be two pipe sizes greater than the pipe passing through the wall.

International Residential Code, Page 620

Engineering Controls for Air ContaminantsvsProtective Equipment for Air Contaminants

Engineering controls (e.g., ventilation) are the preferred method for achieving permissible exposure limits; protective equipment is used only when engineering controls are not feasible, and must first be approved by a competent industrial hygienist.

29 CFR 1926, Subpart D, §1926.55(b)

Key Terms

Vent System (IRC R202) International Residential Code, Page 26

Piping installed to equalize pneumatic pressure in a drainage system to prevent trap seal loss or blowback due to siphonage or back pressure, per IRC Section R202.

Offset (IRC R202) International Residential Code, Page 21

A combination of fittings that makes two changes in direction, bringing one section of pipe out of line and into a line parallel with the other section, per IRC Section R202.

Rough-In (IRC R202) International Residential Code, Page 23

The installation of all parts of the plumbing system—including DWV, water supply, and built-in fixture supports—that must be completed prior to fixture installation, per IRC Section R202.

Slope (IRC R202) International Residential Code, Page 24

The fall of a line of drainage pipe relative to a horizontal plane, expressed as fall in units vertical per units horizontal (percent), per IRC Section R202.

Existing Installations (IRC R202) International Residential Code, Page 16

Any plumbing system regulated by the code that was legally installed prior to the effective date of the code, or for which a permit to install has been issued, per IRC Section R202.

NSF 14 Certification (IRC P2609.3) International Residential Code, Page 621

Third-party certification standard to which all plastic pipe, fittings, and components must conform before use in a residential plumbing system, per IRC P2609.3.

Backfill Protection Requirement (IRC P2604.3) International Residential Code, Page 620

Backfill material must be free from rocks, broken concrete, and frozen chunks until the pipe is covered by not less than 12 inches of tamped earth, per IRC P2604.3.

Building Sewer (IRC R202) International Residential Code, Page 13

The part of the drainage system that extends from the end of the building drain and conveys its discharge to a public sewer, private sewer, or individual sewage-disposal system, per IRC Section R202.

Asbestos TWA PEL (29 CFR 1926.1101(c)(1)) 29 CFR 1926, Subpart Z, §1926.1101(c)(1) and (i)(1)

The permissible exposure limit for airborne asbestos is 0.1 fiber per cubic centimeter of air as an 8-hour time-weighted average; protective clothing is required when exposures exceed this limit.

Fitting Allowance (Threaded Pipe) Mathematics for Plumbers and Pipefitters, Page 39

The distance between the end of the pipe inside a fitting and the center of the fitting; it equals center-to-face minus thread-in, and must be subtracted from center-to-center measurements to find end-to-end pipe length.

Gallons per Cubic Foot Conversion Mathematics for Plumbers and Pipefitters, Page 172

One cubic foot of water equals approximately 7.5 gallons; used to convert tank or pipe volume in cubic feet to gallons.

Building Drain (IRC R202) International Residential Code, Page 13

The lowest piping that collects discharge from all other drainage piping inside the house, extending 30 inches in developed length beyond exterior walls to the building sewer, per IRC Section R202.

Equivalent Noise Exposure Factor (Fe) (29 CFR 1926.52(d)(2)(ii)) 29 CFR 1926, §1926.52(d)(2)(ii)

Calculated as the sum of each period's actual exposure time divided by its permissible time (Fe = T1/L1 + T2/L2 + …); if Fe exceeds 1, the combined noise exposure exceeds permissible levels.

Hazard Communication Standard Reference for Construction (29 CFR 1926.59) 29 CFR 1926, §1926.59

The hazard communication requirements applicable to construction work are identical to those set forth at 29 CFR 1910.1200, covering safety data sheets and chemical hazard communication.

Testing Gauge Increment Requirement (IRC P2503.9) International Residential Code, Page 618

For plumbing tests requiring 10 psi or less, the testing gauge must have increments of 0.10 psi or less.

Formulas to Know

End-to-End Pipe Length (Threaded, two identical fittings)e-e = c-c − [2 × (center-to-face) − 2 × (thread-in)]

Fitting Allowance (Threaded)Fitting Allowance = Center-to-Face − Thread-In

Fitting Allowance G (Copper/Solder)G = Center-to-Face − Depth of Solder Cup

Gallons in a VolumeGallons = Cubic Feet × 7.5

Equivalent Noise Exposure FactorFe = (T1/L1) + (T2/L2) + … + (Tn/Ln) [exceeds limit if Fe > 1]

45°/60° Combination Offset — Alternate PositionRise = 1.414 × Offset; Setback = Offset; Diagonal = 2 × Offset

Valve Cut-In: End-to-End Pipe Adjustmente-e = c-c − (Fitting Allowance, side 1) − (Fitting Allowance, side 2)

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