<p>Hydrocarbon solvents are known for their low toxicity, high volatility, excellent cleaning capability, and environmentally friendly properties and are frequently employed as solvents in ultrasonic cleaning. However, their fire and explosion risks have often been neglected. This study explored the safety concerns and thermal hazards associated with the recycling of hydrocarbon solvents. Solvent samples collected at several stages of the ultrasonic cleaning process were thermally analyzed, and their inflammability was tested. Recycled solvent was found to have a higher flash point temperature than that of the pure solvent (49.7 vs. 47.1&#xa0;°C) and to exhibit exothermicity. Furthermore, the explosion limit range of the recycled solvent (1.06–10.27%) was 76% wider than that for the pure solvent. The recycled solvent had lower thermal stability and higher susceptibility to chemical reactions compared with the pure solvent. Repeated use inevitably alters the characteristics of a hydrocarbon solvent. In addition, solvents can become contaminated with impurities during the ultrasonic cleaning process, and this contamination can increase the risks of fire and explosion. Therefore, during the ultrasonic cleaning process, process conditions should be strictly monitored to ensure the safe use of hydrocarbon solvents and to minimize potential hazards.</p>