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Overlooked code requirements.

Safety Guardrails Near Roof Edge

In my own experience, this may be the single most commonly and egregiously overlooked code requirement in HVAC practice, in consideration of how potentially catastrophic its omission may be. The 2012 International Mechanical Code (2) Paragraph 304.11 requires guards to be provided where appliances, equipment, fans or other components that require service ... are located within 10 ft (3 m) of a roof edge or open side of a walking surface and such edge or open side is located more than 30 in. (762 mm) above the floor, roof or grade below. That clause goes on to say the guard needs to extend at least 30 in. (762 mm) beyond each end of the item of equipment, and the guard must be at least 42 in. (1.07 m) tall designed not to pass a 21 in. (533 mm) sphere (for example, a 42 in. (1.07 m) two-pipe handrail). Specific requirements for the loading withstand rating of the guard rail are given in the International Building Code. (3)

The reason for this requirement is obviously one of safety for the mechanic who may be required to change a fan belt, replace filters, and perform routine service or major repairs. Imagine a worker tugging on a broken fan belt or a filter stuck in its housing that suddenly breaks free, sending the worker stumbling backward. Even a simple accidental slip or fall, especially when the roof is wet or icy, could be fatal. Although I quoted above from the 2012 IMC, the same clause has appeared in every edition since 2000 albeit with different paragraph numbering, and was even found in the now-obsolete BOCA Building Codes as far back as 1993. Yet as I drive throughout my own hometown and on business travel throughout the Midwest, I observe many rooftop units and condensing units located very close to a roof edge with no guard rail at all, or at most an insignificantly short parapet.

If you don't want to deal with a guard rail on the roof edge, or if architectural aesthetics (e.g., a historic building) dictate that one should not be applied, then clearly annotate on roof plan drawings that all mechanical equipment must be installed more than 10 ft (3 m) from a roof edge at closest approach.

Insulation Required on Hot Surfaces

When visiting central plant mechanical rooms and air-handling equipment rooms, I typically see insulation very carefully applied continuously throughout a network of chilled water piping, including on valves, fittings, strainers, and specialty items. This occurs especially but not exclusively in humid climates, as continuous insulation on cold-surface piping is needed to avoid condensation. Very often, however, those same elements lack continuous insulation on steam and hydronic hot-surface valves, fittings, strainers, air separators, and other specialties, and even pumps; instead they feature insulation only on straight pipe lengths.

The energy losses from these uninsulated elements can be substantial and is generally not allowed by ASHRAE Standard 90.1 (4) except for some elements of small piping. Moreover, these uninsulated surfaces pose a safety hazard and may not meet code or OSHA requirements. For our international readers, OSHA is the Occupational Safety and Health Administration, an agency of the U.S. Department of Labor. OSHA regulations (5) mandate that all exposed steam and hot-water pipes within 7 ft (2.1 m) of the floor or working platform shall be covered with an insulating material or otherwise guarded to prevent contact.

Bare metal steam piping or hydronic hot-water piping is a burn risk for personnel assigned to maintenance or repair work in the vicinity of those hot surfaces. It is not difficult to imagine a mechanic performing maintenance in a crowded mechanical room on one piece of equipment while accidentally making skin contact with an adjacent uninsulated steam pipe. Or imagine a worker on a ladder re-lamping a light fixture who begins to lose balance and, as an involuntary human reaction, reaches out a hand to the nearest object for self-bracing--and that nearest object is a bare steam pipe fitting. Even above a lay-in ceiling, a worker may be assigned to repair a VAV box and accidentally touches a nearby bare reheat pipe fitting. In consideration of this, the author does not recommend limiting insulation to the lowest 7 ft (2.1m).

It is clearly not unreasonably difficult to insulate valves, fittings, strainers, and pipe specials because it is done frequently on chilled water piping systems for condensation control. The same should be done for hot surfaces, and it is even easier to accomplish since a vapor barrier is not needed and because removable valve/fitting blankets and covers are available for hot water and steam systems. OSHA allows issuance of personal prot ective clothing to workers in lieu of insulating nearby hot surfaces, but it is difficult to imagine a mechanic successfully rebuilding the seal on a pump near an adjacent hot surface while dressed in bulky clothing and wearing heavy, thick insulated gloves.

OSHA does not specify a specific temperature threshold above which insulation is required nor below which insulation is exempt, and this maybe relevant as hydronic hot water design temperatures in our industry are falling with the growing application of condensing boilers. For help in that regard, we can turn to ASTM Standard 0055-03, (6) which points out that touching of a metallic surface at or above 158[degrees]F (70[degrees]C) causes irreversible injury to human skin almost instantaneously upon contact, and faster than human reaction can withdraw. Metallic surfaces at or below 111[degrees]F (44[degrees]C) appear to pose no safety threat according to the same Standard. 140[degrees]F (60[degrees]C) seems to be a reasonable threshold because it correlates to a first-degree burn (the least severe type of burn) at a contact duration of five seconds. Furthermore, the Uniform Mechanical Code (7) in Paragraph 1201-3.8.6(A) establishes 140[degrees]F (60[degrees]C) as the threshold above which pipe insulation is required.

Hopefully, this safety concern will eventually fade, as energy concerns are driving designers and engineers to specify high-efficiency condensing boilers operating with low-temperature heating water systems. But steam systems are still prevalent in health-care occupancies and legacy non-condensing hot water systems will still be encountered in retrofit work for many more years, so this author recommends you include a clause in your insulation specifications stating something similar t o: "For piping services denoted as 140[degrees]F (60[degrees]C) or greater, all piping surf aces 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." Where Standard 90.1 compliance is required, all piping elements operating above 105[degrees]F (41[degrees]C) must be insulated except for some elements of piping 1 in. (25 mm) and smaller.

Sidewall Grille Blade Spacing

If an air inlet or outlet is less than 7 ft (2.1 m) above the floor, its maximum allowable blade spacing is 0.5 in. (12.7 mm). This is mandated by NFPA 90A (8) in Article 4.3.73. Technically, that clause is worded as requiring a grille having openings through which a 0.5 in. (12.7 mm) sphere cannot pass; so a grille with wider blade spacing could be used if a 0.5 in. (12.7 mm) mesh screen is placed immediately behind the grille. Although the NFPA does not explain the rationale behind this requirement, it may be related to discouraging the use of an HYAC grille as a place to discard trash or accumulations of other materials that could later become a fire hazard. As is the case with the Safety Guards near a Roof Edge, the cited code requirement is taken from the 2012 edition, but the same clause has appeared for many previous editions as well.

Ceilings are rarely lower than 7 ft (2.1 m) above the floor, but sidewall grilles often can be (for example, return grilles in hospital operating rooms). While the HVAC grille manufacturers do offer the 0.5 in. (12.7 mm) blade spacing, many product lines of HVAC sidewall grilles are catalogued and sold with 0.75 in. (19 mm) blade spacing. Obviously, fewer blades means the grille can be priced lower. The design professional must pay careful attention not only to their air inlet and air outlet schedule to require the correct blade spacing wherever the grilles will be installed lower than 7 ft (2.1 m) above the floor, but also to product submittals during the construction phase to ensure a lower-cost alternative with wider blade spacing is not being substituted.


Three code requirements that are sometimes overlooked in mechanical design are presented here. Each topic is derived from the author's own experiences found many times while performing property condition assessments or peer reviews of other designs in actual facilities. This column is intended to be used as a summary checklist or a quick reference guide for HVAC design professionals, to avoid repeating these oversights on future building projects.


(1.) Duda, S. 2013. "Lessons from energy audits." ASHRAE Journal 55 (11).

(2.) ICC. 2012. International Mechanical Code.

(3.) IBC. 2012. International Building Code. Chicago: International Code Council, Inc.

(4.) ANSI/ASHRAE Standard 90.1-2013, Energy Standard for Buildings Except Low-Rise Residential Buildings.

(5.) 29 CFR1910.261(k)(ll) Code of Federal Regulations. Washington, DC: US Government Printing Office.

(6.) ASTM Standard C1055-2003 (Re-Affirmed 2014), Standard Guide for Heated System Surface Conditions That Produce Contact Burn Injuries.

(7.) IAPMO/ANSI/UMC-1. 2012. Uniform Mechanical Code.

(8.) NFPA Standard 90A-2012, Standard for the Installation of Air-Conditioning and Ventilating Systems.


Stephen W. Duda, P.E., is assistant director of mechanical engineering at Ross & Baruzzini, Inc. In St. Louis.
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Author:Duda, Stephen W.
Publication:ASHRAE Journal
Article Type:Column
Geographic Code:1USA
Date:Dec 1, 2014
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