There'll be no extensions to the seven-year legal life of 2004-model transport refrigeration units (TRUs), which will expire Dec. 31 if the California Air Resources Board sides with the recommendation of its staff.

CARB's staff said soot pollution from '04 TRUs is "unacceptably high" at grocery distribution centers located near residential neighborhoods, so requests for extensions should not be granted.

Fleets and trucking associations had asked that '04 TRUs be allowed to run for up to 10 years, partly because equipment to clean their exhaust was not readily available. Older TRUs can be retrofitted with diesel particulate filters or re-engined to extend their allowable lives.

"But we will not recommend this because health risks are so high" to people who live near the distribution centers, said Renee Coad, an air resources engineer. Board members will take up the question at their regular meeting in October.

"TRU engine activity at distribution centers is greater than understood to be in the 2004 rulemaking" which set the seven-year limit, said a statement posted Thursday on the CARB website. So it believes that TRU owners should adhere to original rules requiring phase-out of old equipment or retrofitting to make their exhaust cleaner.

The Air Resounces Board ruled years ago that diesel particulates are a carcinogen that causes lung cancer and other maladies. So it established the TRU rules to combat the threat to public health, and also set rules for diesel-powered vehicles.

Older TRU engines can be replaced with newer, cleaner-burning models to meet the rules, or they can be fitted with diesel particulate filters. Level 2 DPFs, which are 50% effective in removing particulate matter, are generally acceptable for under-25-horsepower TRU engines.

Level 3 filters, which are 85% effective, are usually needed for engines of 25 horsepower or more. Such DPFs give the engines ultra-low-emission status and they can be used indefinitely.

Either type of retrofit costs thousands of dollars per unit, suppliers and users say. Smaller operators are especially impacted by the requirements, so some of CARB's rules give small fleets and owner-operators more time to comply.

Requirements for the various model years are posted at CARB's TRU website. Staffers will answer questions at the TRU helpline, 1-888-878-2826.