I am working on the five-year accident history portion of the hazard assessment under the RMP.  Section 68.42(a) tells me to include "all accidental releases from covered processes that resulted in deaths, injuries, or significant property damage on site, or known offsite deaths, injuries, evacuations, sheltering in place, property damage, or environmental damage."  Is there a definition of "offsite property damage" that will tell me exactly what I need to include in my five-year accident history?

The Part 68 regulations do not define "offsite property damage."  In Chapter 3 of the "General Guidance for Risk Management Programs for Chemical Accident Prevention" (40 CFR Part 68), it states that any level of known offsite property damage triggers inclusion of the accident causing the damage in the five-year accident history.  You are not required to conduct a survey to determine if such damage occurred, but if you know, or could reasonably be expected to know (e.g., because of reporting in the newspapers), that damage occurred, you must include the accident.  (Offsite property damage is most likely to occur from explosions.  The damage would include broken glass (in houses, buildings, cars) and structural damage.  Toxic releases could destroy vegetation.  From fires, property damage would include smoke damage, contamination, and, though this isn't likely, fire itself. Shrapnel from an explosion could also cause damage.)