Boundaries and Interfaces

DOE-STD-3024-98

functions. To the extent practical, piping and

Mechanical boundaries should be based on

instrumentation diagrams (P&IDs) should be

components, and not based on a room location.

provided as the system diagram. For a fluid system

Such components may be capable of isolating one

or a ventilation system, the system diagram might be

system from another system. For example, these

some form of a flow diagram. A P&ID is a system

components might be isolation valves or dampers,

flow diagram that also shows the location of

fill and drain valves, vent valves, or safety relief

installed instrumentation and controls. For an

valves. The system boundaries should extend out to

electrical system, the system diagram might take the

and include such interface isolation devices.

form of a one-line diagram. For electronic systems

that involve components such as transducers,

Heat exchangers are typically assigned to the system

bistable voltage comparators, and power supplies, a

from which the heat is being removed, when the

system functional block diagram might be the most

primary function is remove heat; or to the system

informative. For a computer system, the system

that is being heated, when the primary function is to

diagram might take the form of a combination of a

provide heat. Mechanical support components for

hardware diagram and a summary logic diagram.

piping and duct work should be included in the

primary system, unless a separate facility system

The system diagram shall encompass at least all the

has been defined to address such supports

major components provided to meet the

generically.

requirements of the system. The components shown

on the diagram should be identified in the same

Electrical boundaries are usually located at circuit

manner as the equipment is labeled in the field.

breakers. For electrical power distribution system,

Pertinent sizing values should be shown on the

those breakers that route power to other distribution

diagram. For example, a fan may be identified as

points are usually considered to be part of the

10,000 cfm, a pump may be labeled as 250 gpm, an

electrical power system. However, those breakers

electrical transformer may be identified as

that provide power uniquely to a particular system

480V/120V.

are often considered to be part of that system,

instead of the electrical power system. For example,

This section should also describe any operational or

if a particular pump motor gets its electrical power

maintenance features that are beyond the design

from a specific circuit breaker in a panel, the

requirements. For example, a ventilation damper

breaker is assigned with the pump motor to the

position indicator may have been installed in the

pump system. The system boundary for the pump

operations center (in addition to the local position

system would be at the input/line/supply side of the

indicator) as an enhancement due to operational

circuit breaker, not at the load side of the circuit

problems with that particular damper.

breaker.

When instrument air is provided to support the

4.1.2 Boundaries and Interfaces

functioning of a system, the instrument air

It is important to define the boundaries of the system

components that are necessary for the system being

so that components at or near the boundaries are

described to accomplish its functions are usually

classified properly and hence receive appropriate

considered to be part of that system. Where

attention in activities such as the procurement of

applicable, the boundary of the system should

replacement parts and maintenance actions.

extend out to and include the first upstream isolation

valve in the air supply if the system can still

The precise boundaries of the system should

function when the isolation valve is closed.

encompass all components necessary for the system

Sometimes this may be at a check valve associated

to meet all of its requirements. This includes

with an air accumulator.

mechanical boundaries, electrical boundaries, other

support systems boundaries, and instrumentation

The Instrumentation and Controls (I&C) systems

and controls boundaries.

are usually not designated as separate systems but

rather are most often considered integral portions of

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