A couple of months ago we wrote about parameters to consider during the design of new facilities. We discussed:
- ventilation requirements and local exhaust ventilation;
- duct systems, including proper duct material, return air plenums and terminal diffusers;
- mechanical equipment such as air handlers and heating and air-conditioning control systems;
- filtering media and air-cleaning devices; and
- outside air intakes.1
In this issue we shift our focus to the construction phase and the related issues on which we should fix our attention. Construction activities invariably contaminate the building. Depending on the materials affected and the type of contamination, any residuals could potentially affect building indoor air quality over the structure’s lifetime. If we keep our eyes on a few simple rules, it will pay big dividends in terms of worker health and productivity as well as facility maintenance costs down the line. Recent research suggests that improving indoor air quality can increase worker productivity between 1 and 8 percent, with an average improvement of about 3 percent. And, if we stop to consider that the average cost of employee salaries in a typical Class A building is around $150 per square foot, better indoor environmental quality can save an employer around $4.50 per square foot due to improved worker productivity.2
By nature, construction is a messy business. It does not matter whether we are constructing a new facility or renovating an old space, the issues are for the most part the same. However, by developing and following a good construction management plan we can control the mess and greatly reduce the impact on indoor environmental quality during and after the construction process. Two good resources for putting together your construction management plan are the Environmental Protection Agency’s Indoor Air Quality Tools for Schools3 and the Sheet Metal and Air Conditioning Contractors’ National Association’s IAQ Guidelines for Occupied Buildings under Construction.4 These publications discuss five or six controls to implement during your construction project. We have added one or two of our own to round out a comprehensive construction management plan. So let’s get started.
1. Protecting materials
As with life, all construction projects have to deal with the weather. This is unavoidable and can have a major impact on indoor air quality. Coordinate with your building contractor and see if his material delivery schedule makes sense. All stored materials, and especially porous material like drywall, should be protected from moisture and microbial growth. This is much easier once the building shell is dried in. Any water-damaged materials must be discarded and not used in the construction.
2. Controlling sources
Controlling sources involves preventing or eliminating pollutants from entering the building. For example, do not allow vehicles, machinery or equipment to operate or idle near entries, loading docks or air intakes. These practices allow exhaust fumes, which are loaded with carbon monoxide, to flow into the building. Also, ensure that trash and dumpsters are positioned and stored well away from these areas. One other aspect of source control is to locate or move pollution-causing activities (painting, concrete, block or brick cutting, etc.) away from building openings. This control method is also tied to housekeeping and worker education (discussed below).
3. Pathway interruption (ventilation and exhaust)
Pathway interruption takes source control to the next level. When pollution-causing activities must occur inside the building we need to implement steps to isolate these dirty work areas from clean or occupied spaces. We use ventilation and exhaust systems to control and remove pollutants produced by these activities. If the heating, ventilating and air-conditioning (HVAC) system is already installed we can use pressure differentials to keep pollutants generated in dirty areas from getting to clean areas. This strategy often requires building temporary barriers. We can then pump more supply air to the clean area and, if needed, increase exhaust from the dirty work area, preventing pollutants from escaping to the clean sections. Depending on your climate and the local weather, we may also use 100 percent outside air for the HVAC system, thus diluting and venting contaminants, provided we protect the HVAC system (more on this later). One final tactic of this control method involves using local indoor exhaust equipment. Place high-volume evacuation blowers with ducting in the dirty area and near the contaminant source activity to capture and vent the pollutants directly outside.
4. HVAC protection
During construction activities, it is imperative to protect all installed air-handling equipment from dust, insects, moisture and microbial contamination. If the HVAC system is operated during construction, it should not be done without filters. Temporary filter media with a minimum dust spot efficiency of 35 percent (MERV* 8 or 9) is recommended. New filter media must be installed when construction is completed and before occupancy.
*Minimum Efficiency Reporting Value
All leaks in the ducts or air handlers must be repaired promptly. Clean or replace any contaminated HVAC equipment or ductwork prior to system start-up.
If the HVAC system is designed with ducted return air (i.e., ductwork under negative pressure), then the return side should be damped off, sealed with plastic or isolated during heavy construction, demolition or pollutant-generating activities.
5. Interior finishes
New construction and renovated spaces are plagued with emissions from adhesives, paints, floor coverings, carpets and furnishings. It is best to control indoor pollutants from these sources using the HVAC system. It is recommended that before applying finishes, the interior spaces should be properly weatherized; that is, drywall and plaster should be cured and show a proper moisture content. One alternative is to run the system 24 hours per day for a minimum of three days at a stable temperature and a relative humidity of 60 percent or less. In addition, operate the system 24 hours per day during the installation of all interior finishes.
We strongly recommend not permitting vinyl wallpaper or other water-impermeable coverings on the interior side of exterior walls. These materials tend to trap moisture and lead to mold growth and other problems.
Finally, give strong preference to the use of carpets, glues, paints and other furnishings with low volatile organic compound (VOC) emissions. This will reduce the volume of contaminants you have to deal with as they cure and off-gas.
We mentioned the importance of scheduling to protect building materials at the beginning. Construction sequencing is also important in minimizing absorption of VOCs by porous materials. This involves ensuring that application of wet and odorous materials such as coatings, paints and sealants is completed before installing absorbent “sink” materials like carpets, ceiling tiles and upholstered furnishings.
In addition, proper timing is essential if your construction or renovation project is in close proximity to occupied adjacent buildings or spaces. Dust, noise and odors common to construction can easily find their way into these areas and negatively affect occupants. Refer back to source control and be sure to keep odorproducing and dusty operations well away from all the outside air intakes and building entrances. Schedule indoor air quality issues, referred to as “time of use” problems, on weekends or after normal hours, when the potentially affected facilities are closed. These include activities such as cleaning (see housekeeping below), roofing projects or floor refinishing. If your project is a renovation, we recommend you re-read the pathway interruption control section and recall the value of isolating work areas from non-work areas.
Perform regular (at least daily) housekeeping to prevent tracking dust and debris from construction areas to clean, nonwork areas. Prior to installation, store building materials in a clean area protected from weather. Before allowing occupants to move in, perform a thorough cleaning to remove contaminants from the building. Keep in mind that some conventional cleaners can be sources of contaminants. Concentrate cleaning activities on spaces to be occupied and the HVAC system. For the HVAC, ensure that all coils and fans are cleaned and filters are replaced with new ones in advance of performing the final test and balance, and especially before conducting baseline airquality testing (which we also strongly recommend).
8. Worker education
The previous section discussed how poor housekeeping and conventional cleaning chemicals could adversely affect indoor air quality. By providing all workers with information and training on how to prevent, control and remove indoor airquality pollutants we can minimize these influences. Just as for finishes, choose cleaning chemicals that are low VOC emitting. Make sure the material safety data sheets (MSDS) are reviewed and kept nearby. Implement a consistent hazard communication program for all employees.
Putting a good construction management plan into effect preceding building projects can go a long way in protecting workers’ health and preventing poor indoor environmental quality. A poor or lacking construction IEQ plan can negatively affect indoor air quality throughout the life of the building. By employing the eight control methods identified above you have done everything possible to protect the health of the construction workers and the building occupants for years to come.
- Vince McLeod, CIH, “The ABCs of IEQ ,” Lab Manager Magazine (May 2010), www.labmanager.com/stips. asp?ID=114.
- Experience Exchange Report, Building Owners and Managers Association International. Washington, D.C. 2009. http://www.boma.org/Resources/benchmarking/ Pages/default.aspx.
- Indoor Air Quality Tools for Schools, Environmental Protection Agency. Washington, D.C. May 2010. http:// www.epa.gov/iaq/schools/.
- IAQ Guidelines for Occupied Buildings under Construction, Sheet Metal and Air Conditioning Contractors’ National Association. Chantilly, Va. 2007. http://www. smacna.org/bookstore/index.cfm?fuseaction=search_r esults&cfid=15451692&cftoken=55647325.