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Indoor Mold Sampling

John Poullain, P.E.

Course Outline

This two-hour online course provides guidelines for indoor mold sampling by surface and air methods. The topics covered include the sources of indoor mold problems and when sampling and testing a building for mold is necessary. The course considers methods to identify and locate mold sources, the effects on indoor air quality, health of the occupants, and ways to prevent mold growth. Some of the methods and devises described are also used to sample other contaminants. The course covers several links and references to informative sources covered in the text topics.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the student will:

Intended Audience

This course is intended for building managers, mold remediators and IAQ professionals.

Benefit to Attendees

The student will become familiar with the causes of mold, its health risks, and suitable actions to take for indoor mold problems. Basic methods for improving indoor air quality and controlling sources of mold growth caused by water and moisture problems are discussed. The student will consider the methods of mold sampling and the importance of a thorough visual inspection. Reference sources are provided for information pertaining to indoor mold problems and appropriate steps for reducing the exposure to occupants.

Course Introduction

The text for this course was prepared by the University of Minnesota as a guide to assist building professionals, building managers and others interested in improving building air quality. Many organizations, governmental and private industry, have published documents for guidance in mold remediation, including the US EPA, OSHA, New York City Dept of Health, Texas Dept of Health and Health Canada.

Molds can be found anywhere, outdoors and in buildings, and are important for breaking down matter. When found indoors mold presents health problems to the occupants and causes destruction of furnishings, building materials and wood frame building structures. Some species produce mycotoxins or mold toxins. Occupants can have asthma attacks, allergic reactions and eye, nose, throat and skin irritations. It should be noted mold problems would not be corrected for the long term after visible mold is removed unless moisture and water problems, which promote mold growth, are also corrected. Mold spores can survive in dry conditions although they will not grow however unless moisture is present.

Mold and Mold Spore

The most important ingredient for mold growth is moisture or water. Indoor mold needs a nutrient and organic material to grow. It will grow on wood, insulation and dirt when moisture is present. Since moisture is necessary, typical places to investigate are leaky roofs and plumbing, leaks into the building from cracks, gutters or poorly designed exterior drainage.

Because mold doesn't need daylight, hidden mold is a serious source of contamination and locations conductive to growth must also be considered. A building having visible mold, water damage, or moldy odors should be assessed without delay. Sources of water or leaking water should be stopped and repairs made to deter mold growth after a building is cleaned up. The goal of the course is to understand the importance of visual inspections and the available options for mold sampling.

Visual Inspection

In order to correctly assess the mold situation in a building a thorough visual inspection should first be performed. This will provide a more efficient sampling and testing for mold and avoid unnecessary costs for sampling or remediation later. A visual inspection may be combined with surface and/or air sampling as deemed necessary to accurately assess a mold problem. Visual inspections should consider:

a. Mold growth and locations. Mold should be visually assessed first for signs of growth and any possible hidden mold should also be considered. If hidden mold is overlooked it can add to poor air quality later. Also some molds, light colored as opposed to black molds, can be overlooked and not sampled.

b. Sources of moisture and/or liquids. The extent of any water damage to building materials such as ceiling tiles, dry wall, cardboard as well as furnishings and the ventilation system should be visually inspected. HVAC systems can promote mold growth in the ductwork, outside air supply systems, filters and drain pans and are always suspected mold locations. Electronic equipment like moisture detectors and boroscopes (wall boring and camera devises) can reveal any hidden sources of mold growth and potential moisture problems in construction materials and determine the extent of contamination without the destructive exploration of wall cavities.

Surface Sampling Methods

Surface sampling includes bulk, tape lift and swab methods. Bulk sampling is destructive and consists of removing portions of material contaminated with mold for lab analysis. A swab will allow sampling in hard to reach places not accessible by the tape lift method. Surface samples will also show the types and any possible reservoirs of mold not yet in the air and thus will allow more attention to some areas and make the mold inspection more efficient.

Air Sampling Methods

Air sampling is the most accurate method to assess how many molds are air borne in the building and which areas may present greater problems for mold exposure. This will quantify the number of mold spores. Some airborne molds may not be discovered by air sampling which gives false results when not sampled properly. A negative test result may not be indicative of the actual mold situation and should not be used to dismiss any complaints from the building's occupants. Also if the sample has captured long chains of spores, such as Aspergilus, additional inspection is warranted because airborne spore chains tend to break up quickly.

Typical active air samplers include:

1. Rotorod Spore Sampler. A portable air sampler with a U-shaped rod rotated by a battery powered electric motor at a high speed. The upright arms of the rod collect spore and other particles by impact on adhesive tape and are microscopically examined to identify airborne particles. Although primarily best used for larger outdoor particles such as pollen grains and fungal spores it has been used indoors with some errors.

2. Burkard Spore Sampler. This sampler operates in a manner similar to the Rotorod but uses a sealed drum, which houses a disk turning at one revolution per 7 days. The disk is covered with adhesive tape to trap spores and can generate a continuous record of the air particles for periods from one day to seven days. Air is sucked into the sealed drum through a slit orifice and is trapped near the orifice by adhesive tape giving a record of airborne particles for a specific time of day. The tape is removed and cut for hourly or daily records and microscopically examined. It has limitations similar to the Rotorod sampler.

3. Anderson Sampler. It can trap different size particles. It uses eight metal sections or rings housed in an airtight cylinder. Each metal section has perforations, which are reduced in size from larger at the top to smaller at the bottom. A motor sucks the air from the top of the cylinder through all the rings and out at the bottom. Plates coated with agar, gelatin made from seaweed for bacteria cultures, trap different size spores with larger ones on the top ring. The speed through the cylinder and perforated metal sections gradually increases down to the bottom plate. Particle sizes can vary from >7micrometers to <3micrometers.

4. Cassette Samplers. The Air-O-Cell uses a 37mm cassette and a calibrated pump operating at a flow rate of 15 lpm as described in the text material. Other variations of cassette samplers use MCE filter cassettes for microscope examination or culture and some use stainless steel venturi devices with microscope slides covered with media for cultures.
A combination of taking both surface and air sampling has the advantage of supplementing each other and gives the best characterization of the area sampled. A toxic mold may be identified on surface samples but may not yet be in the air. In order for sampling to represent the typical conditions in a building, enough samples should be taken over a long enough period of time with regard to the activities in the building. Quality control must be maintained and if not done properly will be a waste of time. Personnel performing the sampling should be trained in the proper methodology and laboratories used for the samples should be accredited and participate in periodic proficiency testing. The American Industrial Hygiene Association (AIHA) performs accreditation for microbial laboratories.

Mold sampling, whether surface or air, is usually felt unnecessary before remediating a building when there are visual signs of mold. Sampling can be expensive and there should be a clear reason to take samples. It can be used to support or disprove a supposition such as the HVAC or the outside air system may be the mold source. Also considered any recent remodeling or alterations to the building maintenance. However situations which may require mold sampling, include:

a. A check to show that the expense of remediation is reasonable for the existing situation.

b. A check to show that remediation was effective and was successfully finished. If occupants still have symptoms associated with mold after remediations are finished, air sampling may be necessary.

c. When person(s) contact a disease known to be caused by certain mold species. The mold should be identified and the source located for medical evaluation.

d. When individuals show symptoms caused from exposure to mold but none was detected by a visual inspection.

e. If mold is suspected from musty odors but not located by visual inspection.

f. If a visual inspection shows the HVAC system, air ducts or air handlers are contaminated from mold, then air sampling should be done the show the extent of contamination in the building

g. Where comparisons of indoor and outdoor air quality are necessary.

h. If mold growing on a surface is suspect it should be determined if it is toxic or not. When surface molds are disturbed thousands of spores are released into the air, putting people at risk.

It has been estimated that people spend as much as 90% of their time indoors at home, in offices, schools, stores or other commercial buildings. This has become a serious health problem since indoor air quality may be poorer than outdoor air quality. Some people including the young, elderly, those afflicted with respiratory diseases and those with reduced immunity systems are especially susceptible to indoor mold. OSHA estimated 30% of Americans work in buildings, which have some type of air pollution. Asthma attacks are often triggered by mold or mold-laden dust and estimated as the forth-leading cause of work absenteeism.

Concern over indoor air quality (IAQ) has generated the sale of air cleaning and purification devises, carbon monoxide detectors, electrostatic filters, ultraviolet germicidal irradiation devises and radon test kits as a means to protect occupants or detect indoor air pollutants. Outside air supply systems are used in buildings with HVAC systems to provide the ASHRAE standards for rates of air exchange. Some gas-phase air filtration systems permit a reduction in outside air, which helps to cut costs. The statistics for number of people affected by allergies, asthma and other respiratory diseases have been increasing for all age groups. Building managers have become aware of the negative effect of an uncomfortable or harmful building environment. Poor indoor air can also impair students' learning ability. Prominent factors of poor IAQ, tobacco smoke and sick building syndrome have received much public attention causing regulatory actions and litigation has pushed building owners to monitor and improve indoor air quality. Mold also is perceived to cause serious harm and long term health problems and some feel it may be "the next asbestos". Just a few years ago some yellow pages had no listings for mold remediation and cleanup.

Sources of mold affecting indoor air quality include:

1. HVAC problems:

a. Inadequate HVAC and filtration and outdoor air supply equipment that do not maintain relative humidity in the ideal 30-60% range and/or keep the inside surface temperatures above the dew temperatures to prevent moisture condensation.

b. Mold contaminated HVAC systems, humidifiers, fresh air equipment, and air ducts and air diffusers.

2. Water sources: leaks from pipes, fountains, restrooms, leaks through exterior walls, roofs, cracks in walls and water in drip pans and water spills.

3. Moisture sources: exhalation of occupants, unvented showers and dryers, humidifiers (humidifier fever), outside air supplies, wet foundations, poorly insulated ceilings, condensation on wall surfaces, room surfaces or within wall cavities.

4. Outdoor mold spores, which infiltrate the building or are discharged by mechanical ventilation using outdoor air supply.

There are many regulations for air quality but most pertain to outdoor air quality and the emission of pollutants into the atmosphere. Until now indoor air quality standards could not be easily developed because there were no monitoring devises available to take accurate measurements. This will still be a problem if the devises limitations and quality control measures are not considered. Indoor air quality is a complex problem which is hard to target because of ever changing types and levels of pollution and the individual's susceptibility and perception of indoor conditions. Factors affecting indoor air are mold sources, operation and maintenance of ventilation systems, moisture and humidity control. Because air and surface cleaning alone cannot remove all indoor mold, mold spores are most effectively controlled by a regime of activities which includes control of moisture and water problems, adequate ventilation and moisture control and adequate air filtration.

Course Content

This course is based primarily on on the University of Minnesota publications, "Indoor Molds-Methods for Monitoring Mold in the Environment", PubH5103 and PubH5104 (2003 Edition, 6 pages), PDF file. The course is also based on the Environmental and Analytical Management (EAM) publication, "Procedures for IAQ Sampling" (2005 Edition, 8 pages), PDF file.

The links to the course materials are:

Indoor Molds-Methods for Monitoring Mold in the Environment

Procedures for IAQ Sampling

For Figs 1 and 2 please refer to the following PDFs:


6 stage D00106~.pdf


You need to open or download above documents to study this course.

Course Summary

This course considers the sources of mold, health risks and methods for mold sampling. Measures to take if indoor mold is a problem and when sampling is considered necessary are discussed. The importance of a visual inspection and the types of samples and requirements are considered. Informative reference lists for indoor mold, the causes, effects on health and necessary steps to control and reduce exposure are provided.

Related Links

For additional technical information related to this subject, please refer to:
The site provides an introduction to health and IAQ, sick building syndrome causes, diagnostic quick reference and diagnostic checklists to target the most likely building pollution problems. Information and reference material about IAQ improvement and point source controls are presented.
IAQ topics for buildings, schools, home, FAQ, information and guidance for air quality regulations.
I-BEAM developed by the EPA for building professionals and other in IAQ for commercial buildings. Guidance with module presentation for IAQ problems and how to solve them.


Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.