Appendix A — Division B
Explanatory Material
A-6.2.1.1. 
Good Engineering Practice
Good Engineering PracticeBuilding Pressurization
New buildings tend to be considerably more airtight than older ones. Consequently,
these buildings may have a reduced pressurization requirement compared to the normal
requirement in order to limit drafts and provide a reasonable level of
comfort.
The humidification and relative pressurization of buildings and individual spaces
in buildings can be significant factors in compromising the on-going performance of
the building envelope and other environmental separators.
In new construction, HVAC designers should take this issue into consideration and
confer with those responsible for the design of the environmental separators so as
to limit stress where these building elements are not intended to resist or
accommodate such loads. In existing buildings, the ability of the environmental
separators to resist or accommodate increases in pressure differential or moisture
loading should be considered before changes are made to the HVAC system.
Radon Control Measures may be necessary to reduce the radon concentration to a level below the
guideline specified by Health Canada.
Further information on reducing the indoor concentration of radon can be found in
the following Health Canada publications:
- “Guide for Radon Measurements in Public Buildings (Schools, Hospitals, Care Facilities, Detention Centres),” and
- “Radon: A Guide for Canadian Homeowners”
(CMHC/HC).
A-6.2.1.3. Structural Movement
This Article is intended to remind designers and installers of
mechanical systems of one aspect of the “good engineering
practice” referred to in Article 6.2.1.1.
In determining how to accommodate structural movement, there
are two important principles to bear in mind:
- The prime concern of the NBC is the safety of people in and around the building, as opposed to protection of the mechanical systems and equipment.
- The nature of the accommodation will vary with the type of movement being considered, taking into account particularly how often the movement is likely to be encountered over the life of the building.
For example, a gas line supported on columns that also support
a crane must be installed in such a way that the movement of the
columns, which occurs many times daily, does not cause the lines
to break, thus creating a hazard. Even if the gas line
installation could somehow be designed to break in a
non-hazardous manner, it would hardly be recognized as good
engineering practice if movement that occurs so frequently could
disrupt the operation of the mechanical system.
On the other hand, earthquakes occur far less frequently and
it would not be surprising to have a non-critical mechanical
system fail as a result of an earthquake. However, even in this
situation, the failure must occur in a manner that does not
create a hazard to building occupants. For example, heavy
mechanical equipment should be properly anchored so that it does
not topple on building occupants during an earthquake. The
design of the anchors should take into account accelerations
consistent with the seismic data given in Appendix C for the location of the building. Part 4 provides guidance on the calculation of the loads such equipment would exert on the
building structure during an earthquake; these same loads can be
used in designing the anchors.
Some mechanical equipment can be an important component of
post-disaster life safety systems. In these cases, the measures
needed to accommodate the movements caused by an earthquake
become even more critical since failure of the equipment would
not be acceptable.
Clearly, complying with this requirement will, in most cases,
necessitate close coordination between the mechanical designer
and the structural designer.
A-6.2.1.7.(2) BC Deleted
A-6.2.1.8.(1) Installation General
Ducts or pipes without dampers or valves are generally not considered
to constitute “equipment” and are therefore not subject to this requirement.
A-6.2.2.1.(4) Ventilation Air Supplied to SuitesThe indirect supply of required outdoor ventilation air to normally occupied spaces
through corridor pressurization or other indirect systems is not permitted.
A-6.2.2.3.(2) Ventilation of Storage Garages
Storage garages are ventilated to protect occupants from exposure
to carbon monoxide and other vehicular exhaust fumes. In certain cases,
such as small two- or three-bay storage garages that are used for
occasional vehicle storage, and where occupants are not present, carbon
monoxide or nitrogen dioxide monitoring devices may be omitted if
the ventilation system is interlocked with a local light switch or
other controls to ensure continuous system operation whenever the
area is occupied. In any event, the ventilation system capacity must
be designed to limit the concentrations of carbon monoxide or nitrogen
dioxide at or below the prescribed values.
A-6.2.2.5.(3) Minimizing Growth of Micro-organisms
Sources for microbial growth causing hypersensitivity, pneumonitis and humidifier
fever include drain pans, spray-water air-washers, contaminated filters, poorly
maintained cooling coils, water incursion into ductwork, cafeteria dishwasher
drainage leaks, high humidity and stagnant water. Some of the control measures are
as follows:
- Drain pans should be pitched toward the drain outlet and the outlet bottom should be flush with the drain pan bottom, otherwise there will be standing water in the pan, exposed to the supply air passing through the cooling section of the air-handling unit.
- Access into air-handling equipment should be provided for maintenance of filters, cooling coils and condensate drain pans located below the cooling coils. Access doors should be large and easy to open to facilitate thorough and regular maintenance. Hinged access doors are preferable to bolted access panels.
- If moisture is added to commercial building ventilation air (such as in hospital operating rooms and dedicated computer rooms) to maintain humidity levels in a designated range (for example, 40% to 50% relative humidity), humidifiers that inject steam or water vapour into central air-handling units or main supply ducts are normally used. Injection nozzles should not be located in air-handling unit plenums or ductwork that is insulated with internal fibrous lining. If the lining becomes wet, conditions conducive to microbial growth will result.
The above only addresses built-in features of an HVAC system that can help to
minimize growth of micro-organisms. Even more important than the built-in features
is a program of regular maintenance and cleaning of those portions of the system
where such growth is likely to occur.
A-6.2.2.6.(1) NFPA Publications Pertaining to the Heating, Ventilating and Air-Conditioning of Spaces Containing Hazardous Gases, Dusts or Liquids
- NFPA 30, “Flammable and Combustible Liquids Code”
- NFPA 30A, “Motor Fuel Dispensing Facilities and Repair Garages”
- NFPA 32, “Drycleaning Plants”
- NFPA 33, “Spray Application Using Flammable or Combustible Materials”
- NFPA 34, “Dipping and Coating Processes Using Flammable or Combustible Liquids”
- NFPA 35, “Manufacture of Organic Coatings”
- NFPA 36, “Solvent Extraction Plants”
- NFPA 40, “Storage and Handling of Cellulose Nitrate Film”
- NFPA 51, “Design and Installation of Oxygen-Fuel Gas Systems for Welding, Cutting, and Allied Processes”
- NFPA 51A, “Acetylene Cylinder Charging Plants”
- NFPA 55, “Compressed Gases and Cryogenic Fluids Code”
- NFPA 61, “Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities”
- NFPA 68, “Explosion Protection by Deflagration Venting”
- NFPA 69, “Explosion Prevention Systems”
- NFPA 85, “Boiler and Combustion Systems Hazards Code”
- NFPA 86, “Ovens and Furnaces”
- NFPA 88A, “Parking Structures”
- NFPA 91, “Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Noncombustible Particulate Solids”
- NFPA 96, “Ventilation Control and Fire Protection of Commercial Cooking Operations”
- NFPA 204, “Smoke and Heat Venting”
- NFPA 303, “Marinas and Boatyards”
- NFPA 307, “Construction and Fire Protection of Marine Terminals, Piers, and Wharves”
- NFPA 409, “Aircraft Hangars”
- NFPA 415, “Airport Terminal Buildings, Fueling, Ramp Drainage, Loading Walkways”
- NFPA 484, “Combustible Metals”
- NFPA 654, “Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids”
- NFPA 655, “Prevention of Sulfur Fires and Explosions”
- NFPA 664, “Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities”
- NFPA “Fire Protection Guide to Hazardous Materials”
A-6.2.2.8.(1) Ventilation and Venting of Crawl Spaces and Attic or Roof Spaces
The cross-reference to Part 5 pertains to unconditioned and unoccupied crawl spaces, and attic or roof spaces, which are effectively within the building
envelope. That is, unconditioned and unoccupied attic or roof spaces are located
between the roof deck and roofing above, and the insulation, air barrier system and
vapour barrier below. Unconditioned and unoccupied crawl spaces are located between
the ground cover below and the insulation, air barrier system and vapour barrier
above. Venting of these spaces has implications for the performance of the building
envelope rather than having direct effects on indoor conditions. The ventilation of
conditioned or occupied crawl spaces and attic or roof spaces must comply with
Part 6.
The requirements in Part 5 are stated in terms of loads that must be resisted rather than in terms of building elements. Thus, the Code user will not find explicit
references in Part 5 to crawl spaces, or attic or roof spaces. Part 5 makes reference to the need for venting environmental separators, i.e., the dissipation
of
heat or moisture.
Sentence 6.2.2.8.(1) requires that crawl spaces be ventilated either by natural (above-grade only) or mechanical means. High
moisture levels within the crawl space can lead to problems such as the formation
of
mould, lifting of flooring or long-term damage to structural components.
Crawl space ventilation cannot be expected to correct moisture-related problems
caused by other factors like inadequate surface drainage from the foundation walls
or improper protection against moisture from the ground. These conditions must be
properly addressed so that crawl space ventilation can meet its intended
objectives.
Several factors favour the use of mechanical ventilation rather than reliance on
natural drafts. Local conditions, such as areas with high water tables, may dictate
the need for mechanical ventilation to remove excessive moisture.
Crawl spaces should be maintained at a negative pressure relative to the
conditioned area above to prevent the migration of moisture into occupied areas.
This can be achieved through the use of an exhaust fan and relying on air transfer
through floor penetrations, such as pipes.
A-6.2.3.8.(5) and (6) Exhausting to Garages
A frequent practice in the design of ventilation systems serving
buildings which have associated parking garages is to discharge exhaust
air from the building to the garage in order to reduce the cost of
heating the garage or reduce the length of the exhaust ducts. However,
this practice entails a certain amount of risk since, when the exhaust
system is not running, stack effect may turn the exhaust outlets into
intakes and exhaust fumes (including carbon monoxide) can be drawn
from the garage into the building. Incorporating a backdraft damper
at the exhaust outlet provides some additional protection but backdraft
dampers are generally not regarded as being very reliable. Therefore
this practice is only permitted in very limited circumstances.
A-6.2.3.8.(6)(b) Air Contaminants
For the purpose of Clause 6.2.3.8.(6)(b), washroom exhaust air is not considered to contain contaminants that would adversely
affect the air quality in the storage garage.
A-6.2.3.8.(12)(b) Operation Diversity Factor
The operation diversity factor has to be assessed for each specific application.
Good engineering practice (see Article 6.2.1.1.) design guidelines can provide information on the subject. Figure A-6.2.3.8.(12)(b), which originates from ASHRAE handbooks, provides an example of factors that can be used for general applications.
Figure A-6.2.3.8.(12)(b)
Operation diversity factor
A-6.2.4.1.(2)(c) Carbon Monoxide Alarms
Battery-powered carbon monoxide alarms are acceptable provided
that they are mechanically fastened in place.
A-6.2.9.2.(2) Temperature of Exposed Piping
Normally piping carrying steam or high-temperature hot water at pressures above
atmospheric (corresponding temperature 100°C or above) will be
insulated to reduce heat losses as an economy measure. Above a temperature of
approximately 70°C, however, a bare pipe can cause a burn to human
flesh coming in contact with the pipe. If pipes above this temperature are normally
out of reach of all persons other than maintenance personnel or are properly
guarded, it would be expected that no insulation would be needed for public
safety.