At a hearing in Washington yesterday, lawmakers pressed product safety and health regulators about their three-year investigation into contaminated drywall, expressing frustration with their progress on all fronts.

Defective drywall, most of it imported from China, releases sulfur gas that can corrode electric wiring and trigger respiratory irritation. An investigation published last year by ProPublica and the Sarasota Herald-Tribune showed there are nearly 7,000 homes built with bad drywall nationwide, but enough material was imported to build at least 100,000 homes.

Witnesses at yesterday’s Senate Commerce subcommittee hearing addressed several questions raised by our coverage, including the still-unknown health effects of sulfur gas exposure, the conflicting government guidelines on how to fix homes built with defective material, the challenges of holding Chinese companies accountable, and whether American-made drywall could also be problematic.

Sen. Mark Warner, D-Va., whose state has at least 400 homes affected by bad board, called the drywall problem one of the most frustrating he’s dealt with in more than 20 years in politics.

Brenda Brincku, a Florida homeowner who has sought relief for problems caused by drywall since 2004, said in written testimony that “the federal agencies working on this problem for over four years have failed us.”

The Consumer Product Safety Commission is leading the federal investigation into drywall. Neal Cohen, the commission’s small business ombudsman, defended the agency’s efforts, but acknowledged that progress has been stunted by a lack of cooperation from Chinese government-owned companies.

The subcommitee’s primary concern was the potential health effects of defective drywall. The Centers for Disease Control and the CPSC maintain that levels of sulfur compounds inside affected homes aren’t high enough to cause long-term health problems, but panel members said they found that hard to believe. Exposure to the sulfur gasses for even short periods can cause coughing, severe headaches and bloody noses. Warner said he had visited a home built with defective board staying just 45 minutes, and felt sick for the rest of the day.

The hearing’s most contentious moment came when Warner asked the Centers for Disease Control representative, Dr. Christopher Portier, “Would you allow your family to live in one of these homes?”

Portier paused before answering, “Probably not.”

Portier said the CDC is working to create a model of indoor air levels of sulfur gas emitted by defective drywall that would allow it to calculate health risks. Results from the study are expected in spring 2012.

Homeowners saddled with bad drywall have long complained that regulators keep changing the instructions for how to fix it. The CPSC first advised homeowners that all electrical wiring should be removed because of fire safety concerns then reversed its position, saying the wiring didn’t necessarily need to be taken out.

Cohen said that all of the CPSC’s decisions were supported by “a high caliber of science.” Still, the commission’s guidelines conflict with those issued last year by U.S. District Court Judge Eldon E. Fallon, who is presiding over drywall litigation in federal court in New Orleans, as well as those issued by Virginia’s housing department.

The Virginia guidelines say that wiring should be left in place, but corroded and exposed surfaces should be cleaned. Virginia housing department director William Shelton, who testified at the hearing, said that it would cost $35 to $50 per square foot to fix a home using this method.

The majority of homeowners interviewed by ProPublica and the Sarasota Herald-Tribune said they couldn’t afford to fix their homes. They’ve sought assistance from state and federal programs, but those options are limited because of the current fiscal environment. As a result, some homeowners with defective drywall have defaulted on their mortgages, gone into debt and endured blows to their credit.

Subcommittee members discussed pressing insurers to pay for drywall damage and asking credit-rating agencies not to penalize people affected by such problems. Freddie Mac is offering loan forbearance to affected homeowners.

Unlike most homeowners who have complained about corrosion and health problems from drywall, Brincku lives in a home built with board made in America, not China.

But as ProPublica and the Sarasota Herald-Tribune reported last year, Brincku has experienced the same problems as homeowners who had defective Chinese material.

National Gypsum, which produced the drywall in the Brincku home, contends that nothing is wrong with their material.

The CPSC studied 11 homes that homeowners said were built with American drywall, determining that five exhibited problems and levels of sulfur compounds similar to those built with Chinese drywall. But since the agency did not check for origin labels on the drywall samples, its findings were inconclusive. The CPSC has said that such labels often don’t exist anyway.

Pressed by Sen. Roger Wicker, R-Miss., Cohen said the CPSC had received more than 70 complaints about domestic drywall, but said it would be impossible to confirm the origins of the board “without ripping out every piece of drywall from a home.”

The subcommittee was eager to learn about the CPSC’s latest correspondence with the Chinese government, which owns many of the companies that produced the defective drywall.

Two years ago, a delegation of CPSC inspectors visited drywall factories and gypsum mines in China. The visit became so tense that an American inspector got into a physical tug-of-war with a Chinese official over a drywall sample.

Relations don’t seem to have improved much since then.

“To date there has been no response from the Chinese manufacturers,” Cohen said at yesterday’s hearing. “They are basically telling us, ‘return to sender’ and that they don’t believe there is a problem with their drywall.”

The CPSC is urging homeowners to seek relief in the courts. Plaintiff’s attorneys are currently trying to get the Chinese to cooperate in legal proceedings taking place in New Orleans federal court.

Several committee members cited the need to pass the Foreign Manufacturers Legal Accountability Act, which would require overseas manufacturers to register an agent in the U.S., to make it easier for U.S. attorneys to file civil and regulatory claims against foreign companies..

“This is a textbook case for why it’s critical that we should be able to reach these Chinese companies,” said Sen. Mark Pryor, D-Ark., who chaired the subcommittee hearing. “One of the basic starting points on this is that Chinese manufacturers should have to register, just like domestic corporations, and European corporations, for service and process.”