At least 20 Portland school buildings are likely to fall apart in an earthquake, seriously injuring or killing people in or near them, according to city data.

As a result, Portland Public Schools is looking at how to pay for safety improvements at the 20 schools at greatest risk, plus a gym, auditorium or classroom wing at eight more.

The district may not have much choice in the matter. Portland officials are preparing to ask the Portland City Council to enact mandatory earthquake retrofitting standards, under which Portland Public Schools could face a 10-year deadline to perform substantial seismic strengthening at each of the 28 schools.

"When these buildings fail, they tend to do so catastrophically," said Carmen Merlo, director of the Portland Bureau of Emergency Management, in a presentation Tuesday to a school bond planning committee. "Schools are an often overlooked casualty of earthquakes."

Portland schools at highest risk during earthquake

Benson High

Cleveland High

Grant High, which will be rebuilt starting in 2017

Jefferson High

Roosevelt High, which will be completely addressed by 2017

Ainsworth Elementary

Beach Elementary

Beverly Cleary K-8: Fernwood building

Buckman Elementary

Creative Science School

Creston Elementary

George Middle School

James John Elementary

Kelly Elementary

Richmond Elementary

Rieke Elementary

Rigler Elementary

Rose City Park School

Wilcox Elementary

Winterhaven School

Alameda Elementary: auditorium only

Capitol Hill Elementary: gym only

Hayhurst Elementary: gym only

Kellogg Middle School: gym

Lent School: classroom addition only

Marysville School: Auditorium and boiler room only

Mount Tabor Middle School: gym and auditorium

Vernon School: gym only

The former Smith Elementary, now closed

source: City of Portland seismic building inventory

City staffers have been working since 2014 to write new rules for making unreinforced masonry buildings safer during an earthquake. The city ranks schools as its second highest priority, outranked only by critical-need buildings such as hospitals and public utility buildings.

According to the city's analysis, 20 schools in Portland Public Schools are chiefly or entirely made of unreinforced masonry and eight more have a gym or other structure on campus that is dangerous. Smith Elementary is also listed as in need of upgrades, but has been closed since 2006.

About 10 other schools -- some private, some in other parts of the city such as in the David Douglas School District -- also are made of unreinforced masonry.

The city's catalogue of buildings at greatest risk of partial collapse in a quake does not always take into account seismic retrofitting that has been done to buildings that were unreinforced when built but may have lots of reinforcements now. School district officials did not have readily available information about which schools have been retrofitted and to what standard. The city proposal is to require a higher level of earthquake safety than the school district has historically created in its aging schools.

Unreinforced masonry buildings pose threats not just to those inside but also to passersby, who could be clobbered by rubble, Merlo said. The buildings can also cause a "co-occurring hazard" where debris clogs streets, making it difficult for ambulances to get to those in need, she said.

The worries about earthquake safety come on top of other schools safety problems caused by lead, radon and asbestos. The school district's failure to disclose and respond to problems with lead in drinking water and hazardous lead paint alarmed parents, teachers and students this spring.

In response, school board members are steering a planned $750 million bond measure to focus more on health and safety concerns. The bond would be the second in what school district leaders say will be a long series of bond issues designed to fully remake all of the district's 80-some school buildings over a 30-year period. Work on three of them - Roosevelt High, Franklin High and Faubion K-8 - is already under way.

When completed next year, those three buildings will be fully compliant with seismic safety standards, district officials say.

The city is still evaluating what level of seismic retrofitting to require, and on what timeline, at all of the roughly 1,800 unreinforced masonry buildings in Portland. It plans to hold public hearings on the issue in September in advance of a planned City Council vote in late October or early November.

The Oregonian/OregonLive's Betsy Hammond contributed to this report.

-- Bethany Barnes

503-221-8153; @betsbarnes