Workplace smoking laws apply to any private employer.
Smoking is prohibited throughout the workplace, except for designated smoking area. Smoking is permitted in designated smoking areas.
In the District of Columbia, smoking areas must have a physical barrier or separate room.
The District of Columbia doesn't specifically require employers to provide workplace accommodations for nonsmoker employees. For smokers, employer is required to provide smoking area.
DC employers must have a written policy that designates a smoking area, and employers must notify each employee orally and post the policy within three weeks after adopting it.
In DC, an employee may not be fired or discriminated against in hiring, wages, benefits, or terms of employment because of being a smoker.
If you want to go right to the source and look up DC law on workplace smoking laws -- or if you're writing a letter to your employer or employee and want to cite the applicable law -- the relevant statute(s) can be found at DC Code Ann. Sections 7-1701 to 7-1703.03. Workplace smoking information is also available in Nolo's books Your Rights in the Workplace, by Barbara Repa (Nolo) and The Employer's Legal Handbook, by Fred Steingold (Nolo).