Unthinkably, another oil rig has exploded off the Gulf Coast. No one died in the explosion that occurred around 9 a.m. this morning, but there have been conflicting reports of worker injuries. An oil slick a mile long and 100 feet wide has already been spotted spreading from the blast site. The rig belongs to Mariner Energy, a subsidiary of Apache Corp — the same company, ThinkProgress reminds us, that recently committed to buying certain BP assets to help generate cash to cover its own oil spill liabilities.

Some digging by Lindsay Beyerstein, an Investigative Fund reporter, has shown the companies share a good deal more than an intertwined balance sheet — like BP, Apache Corp and Mariner Energy have a long record of poor equipment maintenance, as Apache and Mariner have accumulated $750,000 in fines in 2010 alone.

This kind of negligence is staggering — especially since the lives of so many workers are at stake. But it’s beginning to seem like worker endangerment is the rule, not the exception when it comes to oil companies and the contractors they hire to clean up their colossal messes.

For example, there was a shocking investigation this week by the Michigan Messenger into oil spill cleanup efforts at Battle Creek —a spill that dumped 800,000 gallons of oil into a waterway in Michigan in July. The Messenger found that Hallmark Industrial, a Texas company contracted to run the cleanup, was bussing undocumented workers into Michigan from Texas and forcing workers to toil at the spill site for 12 to 14 hours a day, seven days a week. Photographs obtained by the Messenger show oil-soaked workers laboring in hazardous conditions. Workers who agreed to speak with the Messenger said that, among other indignities, they were denied access to bathrooms.

This isn’t the first time Hallmark has been in trouble—earlier this year, the Messengerreported, the company was “visited” by federal immigration officials as a result of the company’s work in Florida on the BP oil spill. Yesterday’s updates on the story offered some positive news—Hallmark has been fired from the Battle Creek cleanup and Michigan OSHA launched an investigation into the contractor’s conduct. But today the Messenger reported that law enforcement officials have also turned on the workers themselves—forty-two werearrested when they attempted to collect wages owed to them by the cleanup contractor. The workers are now being held by Immigration Customs Enforcement at a detention facility in Houston.

Treatment of cleanup workers in the wake of Deepwater Horizon oil spill has been similarly suspect. BP has come under fire for using cheap-to-free labor for cleanup efforts. Not only does the company have its pick of Gulf Coast residents robbed of their livelihoods by the spill; it’s also brought on prisoners from local jails. The Nation’s Abe Louise Young explains that “by tapping into the inmate workforce, the company and its subcontractors [have gotten] workers who are not only cheap but easily silenced—and [they] get lucrative tax write-offs in the process.” Indeed, according to Young’s damning report, businesses like BP can cash in on something called the Work Opportunity Tax Credit every time they hire an inmate.

BP, like Hallmark in Michigan, is also cutting corners on safe working conditions. Federal regulators circulated an internal memo in May detailing “significant deficiencies” in worker safety at Gulf Coast cleanup sites. David Michaels, head of the Federal Occupational Safety and Health Agency, said OSHA found scores of oil-spill workers had been hospitalized for nausea, fatigue, headaches, and dizzy spells. And numerous reports have documented inadequate worker training, access to protective equipment and poor oversight of conditions at cleanup sites.

Already, cleanup workers are getting seriously ill. PBS’s Need To Know found short- and long-term health effects of various toxic exposures during the cleanup effort include increased risk of some cancers and even sudden death.

These revelations are all the more chilling in light of emerging data on the health effects on cleanup workers of the (now) second largest oil spill in US history, the 1989 Exxon Valdez. CNN reported in July on a lawsuit filed by cleanup worker against Exxon; court proceedings stemming from his lawsuit revealed that over half the cleanup workers on that spill reported getting sick. The plaintiff eventually settled with the oil company for $2 million, but his attorney told CNN that as a part of discovery he was allowed to view summaries of health records for the 11,000 other cleanup workers. 6,722 reported falling ill.