Engineering Design & Testing

Background

In a comparison of U.S. (domestic-made) drywall and Chinese drywall, the United States Environmental Protection Agency (EPA) has analyzed drywall samples that were made in the U.S. and in China [1]. The constituents that were found by the EPA included elemental (free) sulfur and strontium. Free sulfur was found in the Chinese drywall, but not in U.S. drywall. In addition, strontium was found to be present in higher amounts in Chinese drywall than in U.S. drywall.

Damage

It is known that some Chinese drywall will emit hydrogen sulfide gas. Hydrogen sulfide gas is corrosive to copper and silver, as well as other metals. It has not been determined how hydrogen sulfide gas is formed within the Chinese drywall. The assumption is that the elemental sulfur reacts with water (moisture) to form the hydrogen sulfide gas.

Chinese drywall has been blamed for damage to a variety of items, including plumbing, heating, ventilating, air conditioning and refrigerating (HVAC-R) equipment and electrical/electronic equipment. Examples of the components that can be damaged include copper pipes and fittings, fire sprinklers, air handlers for air conditioning systems, appliances, furnaces, entertainment equipment and electrical wiring and receptacles. For HVAC-R and electrical/electronic equipment, the majority of the damage is corrosion of exposed copper. 

Damage to other property has also been blamed on Chinese drywall, as well as health issues involving occupants. 

It should be noted that the presence of Chinese drywall does not of itself indicate that the damages as discussed above will occur. It has not been established that all Chinese drywall contains elemental sulfur to form hydrogen sulfide gas.

Identification

For an assertion to be made that damage was the result of Chinese drywall, the damage condition should be verified. The Chinese drywall panels would then need to be identified. The identification of individual Chinese drywall panels is important should panels need to be removed as part of a remediation process. Short of being able to identify individual Chinese drywall panels, all of the drywall panels would need to be removed. The identification procedure established at ED&T would be expected to proceed as follows:

The initial step is to determine whether there exists corrosion damage to accessible copper components in the HVAC-R system and/or the electrical distribution system that is consistent with exposure to hydrogen sulfide gas. Samples of these components may be required to confirm the presence of sulfur in the products of corrosion. 

Assuming that there is hydrogen sulfide related corrosion present, identification of individual drywall panels would proceed. A two step, non-destructive method is employed. The first step uses an instrument to identify each drywall panel by locating the drywall seams. A second instrument is then used to test for the level of strontium within each drywall panel. Sulfur is not used as a means for identifying elements because the difference in the amount of total sulfur present (sulfur found in the calcium sulfate, the main constituent of gypsum, in addition to free sulfur) between the U.S. and Chinese drywall is insufficient for an in-situ identification process. However, a high amount of strontium (according to EPA analysis results) is an indicator that the drywall panel was made in China.

A third step may also be appropriate to conclude that the damage is the result of the presence of Chinese drywall. To further confirm that the drywall is producing corrosive gas, small samples can be removed from selected Chinese drywall panels and subjected to analysis to determine the amount of free sulfur present within the gypsum core.

[1] “Drywall Sampling Analysis”, United States Environmental Protection Agency, May 7, 2009

Prepared by Perry V. Young, P.E., Engineering Design & Testing Corp.,Orlando District Office, pyoung@edtengineers.com