A REPRODUCIBLE METHOD FOR SAMPLING CARPETS

Published: COLOUMNS: MOLD; A Mold Property and Personal Injury Litigation Magazine;
Vol. 3, # 2, p. 4, December, 2003
Contact: Laura Alexander, Harris Martin Publishers; www.harrismartin.com
Author: Joe Spurgeon, Ph.D., CIH

Figures: www.aiha.org/aihce03/handouts/po122spurgeon.htm

INTRODUCTION

Let’s define contamination as mold spores simply lying on a dry surface. This can occur when airborne spores settle onto a carpet, especially during mold-related incidents. Therefore, HEPA-vacuuming and cleaning carpets as part of a mold remediation is a prudent practice. Generally, carpets that are simply contaminated can be cleaned. Unless the user is especially sensitive, a thorough cleaning by HEPA-vacuuming the item is often sufficient. However, we have to be aware that carpets, when exposed to water in either the liquid or vapor form (high relative humidity), can accumulate enough moisture to promote the growth of the settled spores.

If a carpet becomes wet as the result of a water intrusion incident, then colonization can occur. I will define colonization as mold growth within the material, such as the fibers, backing, or padding. Once colonization has occurred, it becomes almost impossible to clean the carpet to acceptable levels. Discarding the carpet then becomes the most cost-effective solution.

If, in general, we can say that contaminated carpets can be cleaned, but that colonized carpets should be discarded, then we have the basis for a rational decision. Following this logic, we would prefer to use a sampling method that can differentiate between items that are simply contaminated and those that are colonized, since the sample results provided by that method allow us to make a decision.

In order to pursue this logic, I have to make the following assumptions:

• A sampling method that collects the sample from the surface of a soft-surface item is only testing for surface contamination. An example is the closed-face cassette depicted in Figure 1.

• A sampling method that collects the sample from below the surface (as well as the surface) is testing for both colonization and contamination. The open-face cassette in Figures 2 is an example of this method.

Since the decision to clean or discard is based on colonization rather than contamination, the preferred sampling method would collect the sample from below the surface, from the interior of the material.

MICRO-VACUUM SAMPLING METHODS

Ideally, a soft-surface sampling method should satisfy the following goals:

• First, it should be quantitative. That is, it should have the ability to detect differences in mold concentrations between two or more items (carpets, chairs, etc.).

• Second, it should be reproducible. By this I mean there should be a reasonable chance that two field technicians would collect samples in the same way, so that the sample results collected on different projects could be compared.

• Third, the sample results should allow the investigator to differentiate between items that can be cleaned and those that should be discarded.

In order to meet these goals, the sample results have to be “standardized” (in this case by area), the sampling parameters have to be constants, and the sampling protocol has to be well-defined and simple to implement.

A micro-vacuum sampling method is one that uses a high-volume air sampling pump (suction device) attached to a filter cassette (sample collection device) to collect mold from surfaces. A closed-face 25 mm filter cassette is often used to collect a weighable amount of dust from a carpet. A short piece of beveled plastic tubing is attached to the inlet of the cassette. The beveled tip is then brushed across the carpet to collect the dust.
However, this sampling method has several limitations that make data comparisons difficult.

I prefer to use an open-face 25 mm filter cassette for sampling culturable fungi and/or bacteria in carpets. The advantages of this method are:

• The open face of the cassette has an area of about 4.9 cm², so sampling 20 different spots yields a reproducible sample area of 98 cm².

• The airflow rate is calibrated at 10 liters per minute, resulting in a reproducible suction force between samples.

• The method not only samples the surface, but the interior of the carpet as well. This sampling method attempts to detect colonization as well as contamination.

If the objective is to sample for culturable fungi, then a standard 25 millimeter (mm) filter cassette can be used as the collection device. If a fast turn-around spore count is required, or if both total spores and culturable fungi are being sampled, then a dual-trace Bi-Air cassette may be used as the collection device. The sample results are reported on an area basis (mold per 100 square centimeters of carpet) [mold/100 cm²], for example.

SAMPLING CARPETS

The carpet is sampled by attaching a filter cassette to a high-volume pump, calibrating the airflow rate, and firmly holding the open-face cassette against the carpet for 5 seconds. This applies a reproducible suction force to the carpet, and collects spores from deep within the carpet and backing. The cassette is lifted from the carpet and firmly placed onto a second area of carpet. This is repeated until a known area of carpet has been sampled, typically 100 cm² with a 25 mm filter cassette and 20 cm² when using a Bi-Air cassette. The sampling parameters are detailed in Table 1.

Table 1. Sampling Parameters for Using the Open-face Cassette.

This sampling method is simple to implement - just hold the cassette against the carpet for 5 seconds, then repeat. In addition, the sampling parameters are constants rather than variables, so two field technicians collecting samples on different projects can apply the method reproducibly. A key point is that this sampling method was developed to detect colonization, by collecting the sample from deep within the material.

The sample results may be interpreted in two ways. First, even though numerical guidelines are presented in this article, professional judgment remains the basis for evaluating industrial hygiene data, and is primary in assessing the data. Second, the condition of the carpet can be assessed by evaluating both the concentrations and types of fungi detected.

Based on previous work using this method [AIHAJ, Nov./Dec., 2003], I use the criteria in Table 2 to interpret the sample results. The numerical guidelines in Table 2 are helpful in assessing the condition of a carpet, especially if limited sampling was performed, or if comparison data are not available. However, as previously stated, professional judgment is the primarycriterion for evaluating the sample results.

Table 2. Criteria for Evaluating Carpets (cfu/100 cm²).

Examples of environmental fungi include Cladosporium, Epicoccum, and basidiospores; while contaminant fungi include Aspergillus, Penicillium, Chaetomium and Stachybotrys.