I work for a manufacturing company. My coworkers and I have been meeting for about a month to talk about safety concerns; there are a lot of accidents at our worksite, and we believe the company could be doing more to protect us from injuries. Last week, the company decided to investigate one accident in which an employee was hurt. The investigator interviewed me about the incident this morning, and he told me I could be disciplined or fired if I talk about the incident with anyone. I'm glad the company is starting to take these problems seriously, but can they really prohibit us from talking about workplace events? Are my meetings with coworkers grounds for discipline or termination?
Confidentiality requirements can serve legitimate goals. For example, if your company was investigating whether your injured coworker was under the influence of drugs or alcohol at the time of the accident, the company could have a very real interest in keeping its investigation quiet. Otherwise, the coworker -- and others who may be using drugs or alcohol at work -- might act quickly to destroy evidence or try to influence the testimony of witnesses.
Another legitimate reason for a confidentiality requirement is to prevent employees from comparing notes to come up with a consistent story to explain wrongdoing. For example, if an employee complained of widespread sexual harassment in the form of sexist jokes, lewd comments, and pornography in the workplace, the investigator might well need to prohibit witnesses from speaking to each other about the investigation. Otherwise, the coworkers accused of misconduct might reveal the investigator's questions to each other, so they can come up with an innocuous explanation. In both of these examples, imposing confidentiality during the investigation serves the higher purpose of allowing the employer to find out what really happened.
However, as your question shows, broad confidentiality requirements can have negative effects as well. They can prevent employees from talking to each other about important workplace concerns. A confidentiality requirement, by definition, stops the flow of information about the incident under investigation. This may be great from the employer's perspective, especially if the incident could lead to bad publicity, embarrassment, or legal liability. For employees, however, a confidentiality requirement can interrupt efforts to improve working conditions.
Recently, government agencies have started to push back against employers who impose broad confidentiality requirements during investigations. In a letter to an employer, the Equal Employment Opportunity Commission (the federal agency that enforces the laws prohibiting workplace discrimination and harassment) stated that threatening to discipline or fire employees who discussed a sexual harassment complaint with anyone was illegal retaliation. Discussing harassment complaints with others is a form of "protected opposition" to illegal practices under Title VII. The letter also indicated that employees subject to such a confidentiality rule might believe they could be disciplined or fired for discussing harassment with the EEOC.
The National Labor Relations Board (NLRB), which enforces federal labor laws, has taken a similar approach. In the case of Banner Estrella Medical Center, an HR consultant asked employees who had made a complaint not to discuss the matter with coworkers while the investigation was ongoing. The NLRB found that this request violated employees' rights to discuss the terms and conditions of employment with each other. Prohibiting employee discussions of an ongoing investigation is allowed only if the employer can show that it has a legitimate business justification outweighing the employees' rights. For example, if a witness needed protection, evidence was in danger of being destroyed, testimony was in danger of being fabricated, or the employer needed to prevent a cover-up, these facts could justify a confidentiality requirement. However, the requirement must be based on facts specific to the investigation, rather than a general, blanket approach to all investigations.
What does all of this add up to in your case? It's impossible to say without knowing more facts. On the one hand, workplace safety is a classic example of a topic that employees must be allowed to discuss with each other. Therefore, the company certainly cannot prohibit you and your coworkers from discussing your safety concerns. On the other hand, there may be legitimate reasons for your employer to require confidentiality as to this particular investigation. Perhaps your company is also concerned about the safety record of your worksite, and one of the investigation goals is to discover whether managers are ignoring legitimate safety concerns. If this were the case, confidentiality might be necessary to allow the company to examine manager behavior without sounding any alarms.