Biosolids Thermal Dryer Safety Fact Sheet - The Fundamentals for Managing Risks of Fires and Explosions

Since the 1920s, thermal drying has produced easily handled, virtually pathogen-free biosolids that promote the beneficial use of nutrients present in wastewater solids. However, thermal-drying systems can be hazardous to operate. Managing this sometimes friable, combustible, and self-heating product can be a challenging task for operators, and some components of a dryer system can be at risk of fire or explosion. Recent reports of incidents at biosolids drying facilities underscore the benefits of information covering the fundamentals of the hazards and the means to provide safety for personnel and prevent interruption of solids treatment. To bring awareness to this hazard and mitigation measures, the WEF Biosolids Bioenergy Subcommittee Thermal Dryer Task Force developed and published a Biosolids Thermal Dryer Safety Fact Sheet. The safety fact sheet is directed to persons involved with operating, maintaining, and designing biosolids thermal dryers and reviews the fire and explosion safety hazards associated with thermal drying of biosolids and offers both prevention and mitigation measures to address these hazards at water resource recovery facilities. It also summarizes applicable codes and identifies additional resources that may be consulted for further research, education, and remediation. This paper will review and supplement information in the Safety Fact Sheet. The first section will cover explosion and fire safety hazards related to drying biosolids, including: - Why do thermal-dried biosolids pose risks for fires and explosions? - What factors increase the risk for fires and explosions? - What dryer components pose heightened risk? (Shown in Table 1) The second section will cover protection measures to prevent fires and explosions, such as inerting, temperature control, and water and chemical suppression, as well as mitigation measures to minimize hazards to personnel and damage to equipment, such as deflagration venting and isolation of equipment. The third section will cover industry standards and regulations with special focus on applicable NFPA standards as shown in Table 2. The paper will conclude with information on additional resources for understanding the hazards and design and operational guidance for preventing and mitigating those hazards.