Yes, IOSHA regulations apply to employers of all sizes.
The US Department of Labor has published the "OSHA Handbook for Small Businesses" (OSHA 2209). The intent of this handbook is to assist small business employers in meeting the legal requirements imposed by and under the authority of the Occupational Safety and Health Act of 1970, and to achieve an in-compliance status voluntarily prior to an inspection performed. It may be downloaded from http://www.osha.gov/Publications/osha2209.pdf.