November 5, 2008
Floods and hurricanes create optimal conditions for mold growth. Following hurricanes Katrina and Rita in 2005, an assessment of homes in New Orleans and surrounding parishes identified an estimated 46 percent (>100,000 homes) with some mold contamination, and approximately 17 percent (40,000 homes) with heavy mold contamination.1 Since exposure to certain airborne molds may cause allergic reactions or illness, OSHA recommends that employers consider the National Institute for Occupational Safety and Health (NIOSH)-approved respiratory protection for workers exposed to molds from a variety of sources.2
Ideal environments for mold
Flooding, particularly when waters remain for days or weeks, provides an almost optimal opportunity for mold growth. After prolonged exposure to moisture, mold can grow on building materials, rotting waste material, decaying vegetable materials and other debris. Since molds need both moisture and nutrients to grow, building materials â€” including wood, wallboard, wallpaper and upholstery â€” are ideal nutrient sources.
Mold growth can occur in a relatively short time, so building contents constructed of absorbent materials (paper, cloth, wood, etc.) that have been wet for more than 48 hours are likely locations. While disposal is typically the only remediation option for these materials, smooth, hard surfaces such as metal and plastics can often be cleaned effectively.
Mold spores easily become airborne
Molds reproduce by means of tiny spores that range from 2 microns (mm) – 10 mm aerodynamic diameter. These small spores easily become airborne, and disturbing them in any manner can result in higher air concentrations. Aerosolization occurs in many ways, including disturbance of mold-contaminated areas during clean-up and remediation. Molds can also release low levels of volatile organic compounds (VOCs) thought to be the source of mold/mildew odors.
The Centers for Disease Control and Prevention (CDC) reports that people with asthma, allergies or other breathing conditions may be more sensitive to mold. Those with immune suppression (people with HIV infection, cancer patients taking chemotherapy, and people who have received an organ transplant) are more susceptible to mold infections.3
Respirator selection for mold
The general approach to respirator selection requires knowledge of the specific contaminant, the air concentration and the occupational exposure limit such as the OSHA permissible exposure limit (PEL) or the threshold limit value (TLV) published by the American Conference of Governmental Industrial Hygienists (ACGIH). In the case of mold, lack of recognized exposure limits requires use of other criteria in the selection process.
For mold clean-up in buildings, the U.S. Environmental Protection Agency (USEPA) and the New York City Department of Health have published recommendations for selecting respirators for remediation activities based upon the size of the contaminated area.4,5 EPA offers the following general guidelines for respirator selection:
- For areas less than 10 square feet, an N95 filtering facepiece respirator approved under 42 CFR Part 84 may be used in combination with non-vented goggles.
- For areas between 10 and 100 square feet, an N95 filtering facepiece respirator, or either a half mask with non-vented goggles or full facepiece respirator with 100 level particulate filters (e.g., P100) should be used.
- For areas greater than 100 square feet, a full facepiece respirator with 100 level particulate filters should be used.
For low-level microbial VOCs that may be produced by mold, a carbon-loaded particulate filter offering nuisance-level organic vapor relief, or an organic vapor cartridge used with a particulate filter may also be used. Gases and vapors associated with disinfectants (chlorine, chlorine dioxide, ammonia, etc.) should be evaluated, and may also warrant the use of an appropriate chemical cartridge with a particulate filter.
In many cases, respirators used for mold exposures may also be used for other anticipated air contaminants as well. Employers must select respirators based on OSHA requirements under 29 CFR 1910.134 Respiratory Protection Standard. A comprehensive exposure assessment conducted by a qualified health and safety professional is recommended prior to completing work tasks in flood and hurricane clean-up areas.
Respiratory protection program
Employers providing respiratory protection must comply with all requirements of OSHA’s Respiratory Protection standard, 1910.134, including, but not limited to, medical evaluations, training and fit testing prior to using respirators (refer to table). The following Web sites offer additional discussion of worker protection during natural disasters.
- CDC. “Mold Prevention Strategies and Possible Health Effects in the Aftermath of Hurricanes and Major Floods”. MMWR Recommendations and Reports. June 9, 2006. Available at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5508al.htm
- OSHA. OSHA Fact Sheet: Fungi Hazards and Flood Cleanup. DSTM 9/2005. http://www.osha.gov/OshDoc/data_Hurricane_Facts/Bulletin3.pdf
- CDC, Protect Yourself from Mold. Available at http://emergency.cdc.gov/disasters/mold/protect.asp.
- USEPA. Mold Remediation in Schools and Commercial Buildings. 2001. NYC Department of Health, Bureau of Environmental & Occupational Disease Epidemiology. “Guidelines in Assessment and Remediation in Indoor Environments”.