Donaldson P532504 AIR FILTER, SAFETY RADIAL SEAL. Safety filters have two functions: to act as a backup to the primary filter and to protect the engine during primary filter servicing. ? Serve as a backup filter in case of primary filter damage or improper installation. ? Prevent contaminants from entering the clean side of the air intake system during primary filter servicing. ? Designed to plug rapidly if contamination finds its way past the primary filter, alerting operators about an issue. ? Recommend that safety filters are replaced with every third primary filter change unless there has been a failure of the primary filter. Most orders shipped next business day with UPS or Purolator having 5 to 10 business day shipping and tracking.