Sustaining Acceptable Indoor Environmental Quality
How does the human element affect risk? And how can RCA help control it?
- By Paul Buckmaster, M.S., CIH, CIEC
- Oct 02, 2009
I'm fortunate to practice industrial hygiene for an employer with millions of square feet of space, the most aggressive modernization plan in decades, and a talented group of leaders, facility managers, engineers, technicians, and ES&H professionals. In this environment, I've had a wonderful opportunity to influence the way we design, build, operate, and maintain our buildings. I've learned that acceptable indoor environmental quality can be achieved and sustained by integrating critical elements into a plan-do-check-act management system approach. These elements include:
- Source control
- Moisture management
- Particulate filtration
- Dilution ventilation
- Pre & post-occupancy evaluations
Together, they form the standard of care used to sustain an acceptable indoor environment. The return on investment associated with this end-state includes: a decrease in the prevalence of building-related symptoms and associated lost time, and an increase in employee morale and productivity. These outcomes are significant because they contribute to our mission readiness and our ability to hire and retain talent.
Source control is the principal strategy used in achieving an acceptable indoor environment. Non-specific building- related symptoms — such as eye, nose, and throat irritation, dizziness, and headache — have been associated with exposure to volatile organic compounds (VOCs). Indoor sources are numerous and include construction and building materials, paints, adhesives, carpet, furniture, and equipment. Our control strategies reduce occupant exposure by selecting low-emitting products during the design, construction, and operation of the building. We published a guidance document in 1999 and have incorporated specifications into the procurement process for the past eight years. Today, we use a number of regulations or certification programs to identify and select low-emitting products for our buildings.
These include: Greenguard Environmental Institute (Greenguard Indoor Air Quality Certified); Green Seal (GS-3 Anti-Corrosion Paints, GS-11 Paints & Coatings, GS-37 Bathroom, Glass & Carpet Cleaners, GS-40 Floor Care Products); Scientific Certification Systems (Indoor Advantage, Indoor Advantage Gold, FloorScore); Carpet and Rug Institute (Green Label Plus); Collaborative for High Performance Schools; South Coast Air Quality Management District (SCAQMD Rule 1113 and 1168).
Construction IAQ Management
When I arrived here in the early 1990s, little was done to isolate construction projects from occupied space. We worked informally with project managers and contractors using generally accepted industrial hygiene practice and Chapter 3 of the 1995 edition of "IAQ Guidelines For Buildings under Construction," published by the Sheet Metal & Air-Conditioning National Contractors Association. We published a guidance document in 2004, and since then, there has been a contractual requirement to develop and implement an IAQ Management Plan for projects larger than 500 square feet. These are reviewed and approved by ES&H staff prior to construction startup. Once the project begins, staff walk the site weekly to ensure conformance. Recently we adopted ANSI/ SMACNA Standard 008-2008 (IAQ Guidelines for Buildings under Construction) as the standard of care.
While mold spores are ubiquitous indoors, mold growth can represent a significant problem and cannot be permitted. When moisture and nutrients are present, spores can colonize the surface of building materials and mechanical system components. Spores and hyphal fragments are eventually released into the air and can cause symptoms in allergic individuals.
We manage moisture in our buildings in several ways and design our HVAC systems with accessible components having cleanable interior surfaces, sloped non-corrosive condensate pans with properly designed traps, and ductwork with double-walled construction or external insulation. Robust operation and maintenance (O&M) programs are critical to mechanical hygiene, so we recently adopted ASHRAE Standard 180-2008 (Inspection and Maintenance of Commercial Building HVAC Systems) as the standard of care. We are currently having a contractor load the tasks and frequencies into our asset management program.
Housekeeping is a critical and oft en overlooked control strategy and provides documented benefits to the indoor environment. For many years, adequate funding was not provided, and we noted an increase in the prevalence of building-related symptoms.
Four years ago, we changed to a performancebased contract and saw an overall improvement in the quality of cleaning services. Six months ago, we developed a green cleaning program document based on Green Seal Standard 42 (Commercial and Institutional Cleaning Services). At present, we are exploring cost-neutral ways to implement select elements until a new contract is in place in 2010.
As part of this initiative, ES&H staff developed a slick guide entitled "Office Hygiene & Greening Your Space." The document discusses the benefits of a clean office, how to prepare personal space so that routine contract cleaning can be accomplished, and how to recycle.
Uncontrolled moisture inside the building envelope can lead to occupant discomfort and damage to building materials and furnishings. A significant moisture source is the water vapor in indoor air. We try to maintain the relative humidity in our buildings below 60 percent. Higher levels support the growth of mold and dust mites on building materials, furnishings, and carpet. Our dry bulb design intent is 72 degrees Fahrenheit. Together with relative humidity, this results in a dew point of less than 57 degrees F. This is low enough to prevent condensation on surfaces in occupied space. Cooler surfaces in mechanical spaces have to be insulated.
Flooding, water intrusion through the roof and wall assemblies, and plumbing leaks and backups are additional sources of moisture that must be controlled.
Germicidal ultra-violet lamps will irradiate the back
of the cooling coil and condensate pan, and we expect them to reduce microbial contamination.
Inadequate building pressurization results in the infiltration of hot, humid outdoor air, another source of unwanted moisture. Because of this, we design and operate our new buildings to maintain a positive pressure of 0.03 Pascal.
The mechanical system produces condensate by dehumidifying the air stream that passes over the cooling coil. Th is must be collected and drained from the condensate pan, or microbial slime will form. Because our air handling units (AHUs) are draw-through, this section of the cabinet is under a significant negative pressure. The condensate trap must be properly designed and installed to promote drainage. (We used to find 30 to 40 gallons of standing water in new AHUs. Five years ago, we started to install AHUs on housekeeping pads or drill through the floor slab to install traps with adequate stem height.)
During forensic investigations to determine the cause of mold growth in new systems, we found two other problems related to the design and operation of our AHUs. First, we observed air velocities in excess of 600 fpm were stripping condensate off the chilled water coil. Th is wet the fiberglass insulation in the first 20 feet of supply duct. Then, we noted steam humidification tubes located downstream of the cooling coil a few feet from the fan inlet caused condensation. These problems were solved by reducing air velocity to 450 fpm and selecting a vendor who designed an AHU with the humidifier located upstream of the cooling coil.
Particulate filtration helps to maintain an acceptable indoor environment in several ways. Filters that are properly selected and installed remove particulate matter from outdoor and return air streams and reduce occupant exposure to allergens such as dust, mold spores, hyphal fragments, pollen, and animal dander. Filters also keep the HVAC system and its components clean. Th is reduces pressure drop, increases the efficiency of heating and cooling coils, and reduces the amount of nutrients present to support microbial growth.
Dilution ventilation refers to the distribution of outdoor air to the occupied space to reduce indoor contaminant levels. ASHRAE Standard 62.1-2007 (Ventilation for Acceptable Indoor Air Quality) provides guidance on ventilation rates and has actually reduced the 2004 criteria for office space from 20 cubic feet per minute (cfm) outdoor air per person to about 17 cfm outdoor per person. We continue using 20 cfm as the design intent because a number of studies show prevalence rates for respiratory symptoms increase as ventilation rates are lowered.
While it is fairly easy to measure volumetric flow rates, we use carbon dioxide as a surrogate for ventilation rates. We collect data on indoor and outdoor levels and use a program to estimate ventilation rates. We'd like to see the maximum delta between indoor and outdoor levels to be ≤ 400 parts per million (ppm). Th is is based on analyses of BASE building data that show a significant increase in the prevalence of respiratory symptoms when this delta is exceeded.
Present and Future Initiatives
Germicidal ultra-violet lamps will be installed in a number of new central AHUs during our next major renovation project in 2010. The lamps will irradiate the back of the cooling coil and condensate pan, and we expect them to reduce microbial contamination.
Like other enlightened organizations, our leadership, real estate leasing agent, and building owners have embraced LEED. To date, we occupy or are constructing nine buildings comprising more than 1.2 million square feet of LEED-certified space. Th is year, we will implement a strategy to achieve LEED-EB certification for two buildings by 2010.
This article originally appeared in the October 2009 issue of Occupational Health & Safety.
Paul Buckmaster, M.S., CIH, CIEC, is a Technical Leader with a defense agency located at Fort Meade, Md. He can be reached at 443-479-0625.