OFFICE MANUAL
One of two manuals that together form the AAR Code of Interchange Rules governing the condition and repair of railway equipment used in interchange service. The Office Manual contains the pricing and billing information used for preparing bills for repair work done on foreign cars. See "Interchange Rules and Field Manual."

ONE WEAR WHEEL
A railcar wheel originally made with enough extra rim thickness to allow a worn wheel to be machined and thus restored to its original shape only once during its life. This type of wheel is the Union Tank Car standard.

OPEN TOP CAR
A hopper car without a roof. Used to carry commodities that can withstand atmospheric exposure.

OPERATING PLATFORM 2 BOARD - 2 WAY
Top platform consisting of (2) longitudinally oriented grating sections (each normally 10" wide) with (2) opposite side access openings in the platform hand railing.

OPERATING PLATFORM 2 BOARD - 4 WAY
Same as 2 board-2 way except with (2) additional opposite end access openings in the platform handrailing.

OSHA
Occupational Safety and Health Administration..

OUTAGE
A measurement of the number of gallons of commodity removed from a full tank usually determined indirectly by measuring to the liquid level in the tank and then consulting a pre-calculated table.

OUTAGE TABLES
Pre-calculated tables showing outages at various liquid levels.

OVERHANG
On a railcar, the distance from the centerline of a truck to the adjacent striker.

OVOM VALVE
A bottom outlet plug valve whose operating shaft extends to the top of the car thereby removing the unloader from a position under the car.