ASHRAE Journal - April 2015 - 54

COLUMN ENGINEER'S NOTEBOOK

a basement chiller to a roof-mounted cooler tower, toilet exhaust ductwork, and so forth. If heating and/or
air-conditioning is necessary or desired in an interior
enclosed exit stairway, the designer's options include:
1. An independent air-handling unit located exterior
to the building (e.g., on the roof) and with supply, return,
or exhaust for the stairwell only ducted directly into the
stairway enclosure without traversing other spaces.
2. An independent ducted air-handling system inside
the building and ducted to the interior enclosed exit
stairway within a rated construction running uninterrupted from intake to terminus, matching the rating of
the stairwell enclosure itself.
3. A fan-coil unit, cabinet unit heater, finned-tube radiator, or the like installed within the interior enclosed
exit stairway. In this case, hydronic branch piping for
connection to the terminal unit is permitted to penetrate the stairwell enclosure with proper sealing and fire
safing of the penetration.

Access & Aisles Around Equipment
Mechanical engineers sometimes complain that architects squeeze too much space out of air-handling unit rooms
or mechanical equipment rooms, as an excuse for not
providing sufficient aisles or service clearance. Electrical
engineers have done an admirable job of demanding
adequate service clearance around electrical gear by pointing out that it is required by their code.7 Now we mechanical engineers have the same ability to say to the architect:
"Look, here it is in the code. We'd love to help you make the
mechanical room smaller but we can't. The code requires
these clearances and we have no choice in the matter."
The 2012 IMC in Section 306 now requires that any
room containing an appliance must be provided with an
unobstructed passageway measuring not less than 36 in.
(914 mm) wide and 80 in. (2 m) high from the door to the
equipment; and a level working space at least 30 in. deep
and 30 in. wide (762 mm by 762 mm) must be provided
in front of the control side for servicing. This means it
is no longer acceptable to arrange an equipment room
such that piping or ductwork must be crawled under or
climbed over in order to reach a chiller, air-handling unit,
or other piece of equipment. Mechanical engineers and
designers should insist on adequate mechanical room
service space and annotate the service aisles clearly on the
drawings, so the contractor knows and understands your
intent to keep those aisles clear.
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Keep in mind fire safety as well. The rationale for the
code requirement of a clear access aisle is not only to
allow a service technician reasonable ability to service the
mechanical equipment. It is also intended to allow, once
the service technician has reached the equipment and
begun work, a clear path of egress out of the room in the
event a fire or other emergency occurs. It is not difficult
to imagine a fire started accidentally by an electrical fault
or a spark from a welder's torch during servicing, and
it would be unacceptable if the service technician were
forced to crawl under ducts, climb over pipes, or shimmy
through very narrow passages in order to reach safety.
For roof-mounted or other elevated equipment requiring
a climb greater than 16 ft (4.87 m) above adjacent grade,
the same section requires a permanent ladder or stair (not
a portable ladder) to access roof-mounted equipment.

Review of Overlooked Code Requirements, Part 1
It is worthwhile to reiterate the three frequently overlooked code requirements from the December 2014
Engineer's Notebook column, to have all of the items
handy in one location for use as a checklist:
1. Guardrails are required where equipment that requires service is located within 10 ft (3 m) of a roof edge
or other platform is located more than 30 in. (762 mm)
above the adjacent floor, roof or grade below.
2. For piping carrying fluids at 140ºF (60ºC) or greater,
all piping surfaces including but not limited to pipe,
flanges, fittings, valves of every kind, strainers, unions,
and other appurtenances should be insulated to avoid
potential for personnel injury via contact with a hot
surface. For Standard 90.1 compliance, this requirement
takes affect at or above 105ºF (41ºC) in most instances.
3. If an air inlet or outlet is less than 7 ft (2.1 m) above
the floor, its maximum allowable blade spacing is onehalf in. (12.7 mm).

References
1. Duda, S. 2014. "Overlooked code requirements." ASHRAE
Journal 56 (12).
2. ICC. 2012. International Building Code. Chicago: International
Code Council, Inc.
3. ICC. 2012. International Mechanical Code. Chicago: International
Code Council, Inc.
4. IAPMO/ANSI/UMC-1-2012, Uniform Mechanical Code. Ontario, Calif.:
International Association of Plumbing and Mechanical Officials, Inc.
5. Taylor, S. 2014. "Restroom exhaust systems." ASHRAE Journal 56 (2).
6. Darwich, A. 2014. Letter to the Editor. ASHRAE Journal 56 (4).
7. NFPA 70-2014. National Electrical Code. Quincy, Mass.: National Fire Protection Association.

ASHRAE Journal - April 2015

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