Medical
air systems are a vital element of all
hospitals and most other healthcare facilities. The engineer must consider
expense, capacity, physical size and weight, space limitations, and mechanical
and electrical utility availability in choosing a system for a particular
project. It is important to coordinate the equipment selections with the owner
as well as other engineering and architectural disciplines.
air systems are a vital element of all
hospitals and most other healthcare facilities. The engineer must consider
expense, capacity, physical size and weight, space limitations, and mechanical
and electrical utility availability in choosing a system for a particular
project. It is important to coordinate the equipment selections with the owner
as well as other engineering and architectural disciplines.
The first priority is life safety.
Medical air is used for respiratory therapy and calibration of medical devices
for respiratory application. Providing clean, oil-free air is mandatory. The
medical air system should not be used to supply air for any other purpose
(e.g., hospital laboratory use) because of the opportunities for contamination
of the distribution system. If a patient inhales medical air contaminated by
oil from a defunct compressor or nitrogen from a brazing purge, the
consequences could be irreversible. In addition, a utility or pipeline shutdown
must be coordinated with the hospital staff to prevent an accidental service
termination while patients are connected to the system. Engineers should be
aware of the requirements before designing any medical gas system.
Medical air is used for respiratory therapy and calibration of medical devices
for respiratory application. Providing clean, oil-free air is mandatory. The
medical air system should not be used to supply air for any other purpose
(e.g., hospital laboratory use) because of the opportunities for contamination
of the distribution system. If a patient inhales medical air contaminated by
oil from a defunct compressor or nitrogen from a brazing purge, the
consequences could be irreversible. In addition, a utility or pipeline shutdown
must be coordinated with the hospital staff to prevent an accidental service
termination while patients are connected to the system. Engineers should be
aware of the requirements before designing any medical gas system.
Distribution Systems
Medical compressed air systems must
be designed to prevent the introduction of contaminants or liquid into the
pipeline. Medical air systems must:
be designed to prevent the introduction of contaminants or liquid into the
pipeline. Medical air systems must:
• be supplied from cylinders, bulk
containers, or medical air compressor sources; or reconstituted from oxygen USP
and oil-free, dry nitrogen
containers, or medical air compressor sources; or reconstituted from oxygen USP
and oil-free, dry nitrogen
• meet requirements of the medical
air
air
• contain no detectable liquid
hydrocarbons
hydrocarbons
• contain fewer than 25 ppm gaseous
hydrocarbons
hydrocarbons
• contain 5 mg/m3 or less of
permanent particulates sized 1 micron or larger at normal atmospheric pressure.
permanent particulates sized 1 micron or larger at normal atmospheric pressure.
In a typical fully functioning
healthcare facility, the medical air is supplied by a high-pressure cylinder
manifold system or a medical air compressor system. Manifold distribution
systems typically are used in facilities that have very little demand for
medical air. Medical air compressor plants typically are for larger facilities.
healthcare facility, the medical air is supplied by a high-pressure cylinder
manifold system or a medical air compressor system. Manifold distribution
systems typically are used in facilities that have very little demand for
medical air. Medical air compressor plants typically are for larger facilities.
Existing facilities may choose to
upgrade their equipment and associated pipeline or add medical air plants as
the facility expands. When selecting a piece of equipment for a new facility,
the possibility of future expansion should be considered. To allow for future
growth, it is good practice to be conservative in sizing a system.
upgrade their equipment and associated pipeline or add medical air plants as
the facility expands. When selecting a piece of equipment for a new facility,
the possibility of future expansion should be considered. To allow for future
growth, it is good practice to be conservative in sizing a system.
Duplex Medical Air Compressor Source
Systems
Systems
An engineer usually has more options
available when designing for a new facility than for a renovation or
replacement project. Electrical and mechanical utilities can be more easily
calculated, and chilled water, ventilation, and electrical services can be
sized and adequately located. The ideal schematic design contains a
well-ventilated, easily accessible mechanical room dedicated to medical gas
equipment.
available when designing for a new facility than for a renovation or
replacement project. Electrical and mechanical utilities can be more easily
calculated, and chilled water, ventilation, and electrical services can be
sized and adequately located. The ideal schematic design contains a
well-ventilated, easily accessible mechanical room dedicated to medical gas
equipment.
In selecting a medical air
compressor for an upgrade, the engineer may have some trouble due to mechanical
utility inefficiencies (e.g., poor chilled water quality, a poorly ventilated
mechanical space). The local electric utility may not support the pump
arrangement, or poor equipment access may require breakdown of equipment parts
at a significant cost increase. It is imperative to conduct thorough surveys of
the surrounding mechanical space and utilities before determining the best type
of compressor for the project.
compressor for an upgrade, the engineer may have some trouble due to mechanical
utility inefficiencies (e.g., poor chilled water quality, a poorly ventilated
mechanical space). The local electric utility may not support the pump
arrangement, or poor equipment access may require breakdown of equipment parts
at a significant cost increase. It is imperative to conduct thorough surveys of
the surrounding mechanical space and utilities before determining the best type
of compressor for the project.
It is a good idea to select more
than one type of compressor at the schematic design phase. You should develop a
master plan that shows existing demand and estimated spare capacity. The owner
may want to obtain a cost estimate before making a final decision.
than one type of compressor at the schematic design phase. You should develop a
master plan that shows existing demand and estimated spare capacity. The owner
may want to obtain a cost estimate before making a final decision.
Types of Compressors
All medical air compressors must be
able to deliver compressed air that does not contain oil. This article
specifically deals with medical air systems for Level 1 hospitals.
able to deliver compressed air that does not contain oil. This article
specifically deals with medical air systems for Level 1 hospitals.
There are three acceptable types:
• Oil-free compressors: These
reciprocating compressors have no oil film on surfaces exposed to air being compressed.
They do have oil in the machine and require separation of the oil-containing
section from the compression chamber by at least two seals. The interconnecting
shaft and seals must be visible without disassembling the compressor.
reciprocating compressors have no oil film on surfaces exposed to air being compressed.
They do have oil in the machine and require separation of the oil-containing
section from the compression chamber by at least two seals. The interconnecting
shaft and seals must be visible without disassembling the compressor.
• Oilless compressors: These
reciprocating or rotary-scroll compressors do not have oil in the machine.
Lubrication is limited to seal bearings.
reciprocating or rotary-scroll compressors do not have oil in the machine.
Lubrication is limited to seal bearings.
• Liquid ring pump: These rotary air
compressor pumps have a water seal. It is recommended that a heat exchanger be
utilized to conserve seal water.
compressor pumps have a water seal. It is recommended that a heat exchanger be
utilized to conserve seal water.
Medical air compressor plants should
be sized to serve peak calculated demand when the largest compressor is out of
service. In an efficient design of a larger system (i.e., three pumps or more),
each compressor is sized to handle an equal percentage of the peak demand and
create redundancy. There never should be fewer than two compressors.
be sized to serve peak calculated demand when the largest compressor is out of
service. In an efficient design of a larger system (i.e., three pumps or more),
each compressor is sized to handle an equal percentage of the peak demand and
create redundancy. There never should be fewer than two compressors.
Accessory Equipment
Several pieces of mechanical
equipment accompany the medical air compressor system:
equipment accompany the medical air compressor system:
• Intake: The compressor's air
intake must be located outdoors, above roof level, and at least 10 ft from any
door, window, other intake, or other opening. Intakes must be turned down,
screened, and equipped with intake filter mufflers. These filters remove large
amounts of particulates (microscopic particles of solid or liquid matter
suspended in the air) and contaminants at the compressor inlet.
intake must be located outdoors, above roof level, and at least 10 ft from any
door, window, other intake, or other opening. Intakes must be turned down,
screened, and equipped with intake filter mufflers. These filters remove large
amounts of particulates (microscopic particles of solid or liquid matter
suspended in the air) and contaminants at the compressor inlet.
• Air receiver: The role of the air
receiver is to store air and balance pressure variations. It must have a
full-size bypass as well as a manual and automatic drain to remove any
collected condensate. It must meet The American
Society of Mechanical Engineers (https://asme.org) Section 8
boiler and pressure vessel construction standards. The receiver is sized based
on system demand, compressor size, and compressor running times.
receiver is to store air and balance pressure variations. It must have a
full-size bypass as well as a manual and automatic drain to remove any
collected condensate. It must meet The American
Society of Mechanical Engineers (https://asme.org) Section 8
boiler and pressure vessel construction standards. The receiver is sized based
on system demand, compressor size, and compressor running times.
• Compressed air dryer: The dryer is
used to remove water vapor from the air stream. At a minimum, it must be a
duplex system valved to allow one unit to be serviced. Dryers should be of the
desiccant twin-tower type, sized for 100% of calculated load at design
conditions. They should be rated for 32°F (0°C).
used to remove water vapor from the air stream. At a minimum, it must be a
duplex system valved to allow one unit to be serviced. Dryers should be of the
desiccant twin-tower type, sized for 100% of calculated load at design
conditions. They should be rated for 32°F (0°C).
• Duplex final filters: These should
be rated for 100% system capacity, with a minimum of 98% efficiency at 1 micron
or greater. The filter must be equipped with a visual indicator showing the
remaining filter element life.
be rated for 100% system capacity, with a minimum of 98% efficiency at 1 micron
or greater. The filter must be equipped with a visual indicator showing the
remaining filter element life.
• Medical air regulators: Regulators
control the pressure of the air system. They should be sized for 100% of the
system's peak calculated demand at design conditions. Pressure regulators
should be set to provide the most distant outlet with 50-psig medical air.
control the pressure of the air system. They should be sized for 100% of the
system's peak calculated demand at design conditions. Pressure regulators
should be set to provide the most distant outlet with 50-psig medical air.
• Alarm sensors: A medical air
compressor must have alarm sensors located nearby where they can be
continuously monitored by hospital personnel. Typical alarms are for high
pressure, low pressure, and other trouble (e.g., lead/lag pump operation, high
temperature, high dew point, carbon monoxide). Additional alarm signals can be
added depending on the type of compressor and the owner's preference.
compressor must have alarm sensors located nearby where they can be
continuously monitored by hospital personnel. Typical alarms are for high
pressure, low pressure, and other trouble (e.g., lead/lag pump operation, high
temperature, high dew point, carbon monoxide). Additional alarm signals can be
added depending on the type of compressor and the owner's preference.
• Anti-vibration mountings: These
should be provided for the compressors, receiver, and dryers, as required by
the manufacturer.
should be provided for the compressors, receiver, and dryers, as required by
the manufacturer.
Piping
Medical air piping is sized
according to the calculated flow rate in cubic feet per minute (cfm).
Compressed air piping is constructed of brazed type-L copper prepared for
oxygen service. The piping must be pitched toward the central plant, have
drains at low points and it must be valved and identified.
according to the calculated flow rate in cubic feet per minute (cfm).
Compressed air piping is constructed of brazed type-L copper prepared for
oxygen service. The piping must be pitched toward the central plant, have
drains at low points and it must be valved and identified.
The flow rate for medical air
outlets generally is 1 cfm. The pipeline flow rate is calculated by counting
the number of connected medical air outlets and applying a use factor. The flow
rate from the total number of outlets is called the total connected load.
Because not all outlets are normally used at the same time, a simultaneous use
factor should be applied to reduce the system flow rate. The rate is then
applied to the sizes of the pipeline and compressors. The American Society of Plumbing Engineers (https://aspe.org/) has developed a table that
quantifies medical air usage in different areas of the hospital.
outlets generally is 1 cfm. The pipeline flow rate is calculated by counting
the number of connected medical air outlets and applying a use factor. The flow
rate from the total number of outlets is called the total connected load.
Because not all outlets are normally used at the same time, a simultaneous use
factor should be applied to reduce the system flow rate. The rate is then
applied to the sizes of the pipeline and compressors. The American Society of Plumbing Engineers (https://aspe.org/) has developed a table that
quantifies medical air usage in different areas of the hospital.
When the total connected load has
been calculated and the use factor has been applied, the main pipeline and
compressor equipment can be effectively sized and selected.
been calculated and the use factor has been applied, the main pipeline and
compressor equipment can be effectively sized and selected.
In summary, engineers must take care
when sizing and specifying medical air equipment to meet the needs of the
healthcare facility and its patients. Before beginning a project, be sure to
review the requirements pertaining to medical gas systems of the most recent
codes. Both the information at hand and technology are developing on a daily
basis, and it is the engineer's responsibility to be informed.
when sizing and specifying medical air equipment to meet the needs of the
healthcare facility and its patients. Before beginning a project, be sure to
review the requirements pertaining to medical gas systems of the most recent
codes. Both the information at hand and technology are developing on a daily
basis, and it is the engineer's responsibility to be informed.
