According to World Health Organization, approximately 3192 deaths and 270,000 deaths are due to fire accidents, in Kenya however, the outbreak of fires have led to deaths and the destruction of property. The schools are the most affected in Kenya but few studies have been carried out to assess the potential causes of fire, the preparedness and mitigation measures. The objectives of this study were; to identify potential causes of fire outbreaks, level of readiness for fire outbreaks, and assess fire safety and prevention measures for fire outbreaks in boarding secondary schools in Nyamira County. A descriptive cross-sectional study design and purposive sampling were utilized. The study population consisted of 50 secondary school principals / deputy principal / senior teachers and 5 Sub-county educational officers. Both quantitative and qualitative data were collected using semi-structured questionnaires and key informant interview guides, respectively. The leading causes of fire outbreaks in boarding secondary schools in Nyamira County are arsonists (90%), electrical faults (88%), short or overloaded circuits (60%), flammable liquids (64%), and other combustible materials (<50%). In addition, most of the schools in Nyamira County had dry chemical extinguishers (76%) and foam cylinders for firefighting (54%), with over fifty per cent of them able to operate them. The majority had an emergency communication system, regular inspection and maintenance of firefighting equipment, and a fire assembly plan in preparedness for fire outbreaks. Most of the boarding secondary schools in Nyamira County had a fire safety policy as a safety and prevention measure for fire outbreaks. Other mitigation measures such as fire insurance policy, evacuation plans, and sanctions were incompletely installed in most schools in the County. This study recommends that the school administration investigate the underlying reasons for the arson attacks. In addition, there should be regular checking of the electrical wiring by the electrician and unplugging electrical appliances when not in use. The school administration should improve fire preparedness by providing other firefighting equipment and fire extinguishers and training the teachers on fire disasters. Further, the schools should put in place a fire insurance policy and enhance the knowledge of the teachers and education stakeholders on the evacuation plan.