This very same question was asked of the Occupational Safety and Health Administration (OSHA) in 1999. Its answer: that an employer is completely liable to an employee injured at home just as if he was injured on the employer's property. This ruling was so controversial that it sparked an outcry in Washington, and within a few weeks the answer was "clarified" (i.e. reversed).
The new, revised answer from OSHA was "We believe the OSH Act does not apply to an employee's home or furnishings. OSHA will not hold employers liable for work activities in employees' home offices. OSHA does not expect employers to inspect home offices. OSHA does not, and will not, inspect home offices." Home manufacturing workshops, however, were found to still be covered, and have to comply with all health and safety standards (and may be inspected if a complaint is lodged).
Is There Liability Despite OSHA's Position?
The Society for Human Resource Management, the world's largest HR association, says that this entire field is still a very gray area, and that a worker injured in a home office while conducting work for their employer that is arranged and approved by the employer is covered legally, and a company is liable for the injury as though it had happened in its main office.
For instance, an employee who slipped on the ice of his own driveway while going to the mailbox to retrieve a company document was found to have suffered a "work related injury" and won a liability lawsuit against his employer. So although OSHA will not actively seek out and inspect home offices for safety violations, an employer can (apparently) still be held liable for work injuries suffered at home, as long as the injury has occurred while the employee is actually working (not just during working hours).
In any case, this whole argument is only regarding OSHA. State employment organizations can have any number of regulations regarding this issue, so contacting a lawyer familiar with state employment is essential to understanding all your options.
Do Any Standards Exist for My Home Office?
Because this is a relatively new field, and the possibility of telecommuting has only arrived with the electronic age, no one is actually sure exactly where the liability line is drawn. For this reason, most employers have enacted various safety measures for home employees in an attempt to ward off liability for any injuries. Some companies inspect home offices before allowing employees to telecommute. Others have set safety regulations for the work place, but may not actually inspect an employee's home. At the very least, most mandate the use of office approved equipment (ergonomic desks, chairs and keyboards, for example).
The bottom line is that it is up to each employer to determine what safety standards should apply to home workers. If you are an employer, it would behoove you to apply the same standards of safety you have at your office for your telecommuting workers to minimize the chances of a negligence law suit.
So When Is the Employer Liable and When Is It Not?
The only rule that is set in stone is that OSHA will not inspect the homes of workers to see if they comply with federal regulations. But all this amounts to is that employers cannot be sued for violating the standards themselves. The question of liability if someone is actually injured has not been legally tested to its limits, so for now it literally depends on the judge and the cases of precedent in your state, as well as your state's law regarding workplace injuries.
For this reason, if you work at home for a company, and are injured in the course of your job, you should contact an employment lawyer or personal injury lawyer in your state immediately. Even if your company has taken preventative measures, it is very possible that it can be held liable for your injury. Your case could be the one that establishes where exactly the law stands in this issue.