Mr. Timlin, upon being told of the comment, initiated an investigation. He and Ms. Lemire interviewed the woman, Chanissa Green, who told them about many racially tinged remarks by another employee, according to the complaint.

“My grandfather owned your father,” the other employee, who was the company’s former comptroller, told her, according to the lawsuit. For some five years, she had heard insults about her family, her hair and her career prospects, the lawsuit says. “That’s how black people do it,” she was told. Another time, when she entered a room, someone said, “We’re in the ’hood now,” according to the lawsuit and papers filed with the Equal Employment Opportunity Commission.

Ms. Green, who still works at the company, did not respond to a message left for her at work.

The investigation by Mr. Timlin and Ms. Lemire “revealed that MSA executives and supervisors were aware of these racist remarks,” the civil complaint states, “and took no action.”

When Mr. Timlin discussed his findings with Mr. Harvey, the company’s chairman, the following month, Mr. Harvey proposed a solution: Mr. Atherall should apologize and the matter need not go further, according to the lawsuit. “I want to make this go away,” Mr. Harvey said, according to the lawsuit, which states that Mr. Timlin recorded the conversation.

Mr. Timlin did not let the matter go. He explained that he later reported his findings to MSA’s corporate board — which included a former Marine general and two bankers with Allen & Company, which owns about a third of MSA Security — according to the suit. In a letter he filed with the Equal Employment Opportunity Commission, he said he recommended that a number of employees be disciplined and recommended a suspension without pay for Mr. Atherall. He also suggested that Mr. Harvey be removed from any decision-making role at the company.

Instead, Mr. Timlin was barred from the offices and was fired in September. His termination notice said he had engaged in “verbal abuse of numerous MSA executives” and had contributed “to divisiveness and polarization within the company,” among other claims.

Mr. Timlin, in his letter to the E.E.O.C., said that his firing was actually in retaliation for “discovering and seeking to properly address a troubling pattern of discriminatory behavior at MSA.”