Afraid of heights? This is not the job for you.

The iconic St. Louis Gateway Arch, an engineering wonder that towers high above the skyline, is now 50 years old. Discoloration on the stainless steel exterior has building doctors climbing 630 feet up the arch to examine the mysterious stains.

TRANSCRIPT

THE ICONIC ST. LOUIS GATEWAY ARCH, AN ENGINEERING WONDER THAT TOWERS HIGH ABOVE THE SKYLINE, IS NOW 50 YEARS OLD.

DISCOLORATION ON THE STAINLESS-STEEL EXTERIOR HAS BUILDING DOCTORS CLIMBING 630 FEET UP THE ARCH TO EXAMINE THE CAUSE OF SOME OF THOSE MYSTERIOUS STAINS.

HERE'S A LOOK.

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WELL, WE ARE BUILDING DOCTORS, AND WHAT WE'RE DOING IS WE'RE DOING A VERY CAREFUL DIAGNOSIS OF THE BUILDING.

BUT THERE IS NO OTHER BUILDING QUITE LIKE IT.

ST. LOUIS'S GATEWAY ARCH, OFFICIALLY THE JEFFERSON NATIONAL EXPANSION MEMORIAL, IS NOW 50 YEARS OLD, AND EXTENSIVE INTERIOR INSPECTION DETERMINED IT IS STRUCTURALLY SOUND.

BUT OUTSIDE, WELL, YEARS AGO PEOPLE BEGAN TO NOTICE THAT THE SHINY STAINLESS-STEEL SURFACE WAS, WELL, STAINED HERE AND THERE, AND THE NATIONAL PARK SERVICE DECIDED IT NEEDED TO KNOW 'IS THAT JUST DIRT, OR IS IT DAMAGE?'

FOR THIS PART OF THE JOB, THE FIRM OF WISS, JANNEY, ELSTNER ASSOCIATES BROUGHT MEMBERS OF THEIR APPROPRIATELY NAMED DIFFICULT ACCESS TEAM.

[ WIND WHISTLING ]

OUR SAFETY MANAGER HAS REFERRED TO THIS PROJECT AS 'MOUNT EVEREST.'

THIS IS THE SAME COMPANY THAT INSPECTED THE STONES AND MORTAR ON THE WASHINGTON MONUMENT AFTER DAMAGE FROM AN EARTHQUAKE.

BUT THE ARCH IS TALLER, AND IT'S CURVED.

ON THE TOP SIDE, THEY WERE ABLE TO RAPPEL UP AND DOWN AND INSPECT ALL THE WELDS.

BUT IT WAS THE UNDERSIDE THAT PRESENTED THE REAL CHALLENGE AND THE MOST INTERESTING AND WORRISOME STAINS.

THE GUY BEING LOWERED DOWN AND ATTACHING HIMSELF WITH SUCTION CUPS IS DAVE MEGERLE.

I WAS THE ONE THAT EVERYBODY SAW RIGHT HERE AT STATION 35, WHERE WE STOPPED AND TOOK SOME SAMPLES.

WE TOOK SOME SILICONE SAMPLES THAT GAVE US THE TEXTURE OF THE STAINLESS STEEL THAT EVERYONE WAS CONCERNED ABOUT.

♪♪ THERE WAS SOME STAINING THERE THAT THEY WANTED TO TEST WITH SOME CLEANING METHODS.

A LOT OF WHAT HE TRIED WERE JUST COMMON HOUSEHOLD PADS AND CLEANERS, BUT IN DIFFERENT PLACES, THEY USED GUNSHOT-RESIDUE TAPE TO PICK UP THE DIRT AND PARTICULATES FOR EXAMINATION UNDER AN ELECTRON MICROSCOPE AND LABORATORY ANALYSIS.

THE FINAL REPORT WOULD NOT COME OUT FOR SIX MONTHS.

SO, WHEN WE'RE LOOKING AT CONSTRUCTION MATERIALS OF ANY TYPE, THEY ALL CORRODE, JUST AS OUR BODIES CORRODE.

IT'S CALLED AGING.

THERE WAS A LOT OF INTEREST IN THIS BY ARCHITECTS, ENGINEERS, AND HISTORIC PRESERVATIONISTS.

AND THE NEWS FOR THE GATEWAY ARCH WAS GOOD.

THE SURFACE DISCOLORATION IS SUPERFICIAL.

IT WILL HAVE NO EFFECT.

IT'S ALL FROM INDUSTRIAL POLLUTANTS, SO I THINK...

IN OTHER WORDS, THE ARCH IS DIRTY AND DISCOLORED, BUT NOT UNIFORMLY.

WHEN IT RAINS, THE TOP SIDE GETS A GOOD WASHING, BUT ON THE UNDERSIDE, THE DIRT COLLECTS ON THE WELDS AND ANY OTHER SCRATCHES AND IMPERFECTIONS.

WHEN THE ARCH WAS NEARING COMPLETION, A METAL BRIDGE, OR STRUT, WAS USED TO KEEP THE TWO LEGS APART, AND THERE ARE NOW STAINS WHERE IT WAS ATTACHED.

SO, THESE ARE THE THREE PLACES WHERE THE STRUT GRABBED THE -- I BELIEVE THIS IS THE SOUTH LEG.

AND AS FOR THOSE STRIPES, THE REPORT SAYS THAT DURING PRODUCTION, THE POLISHING OF THE METAL PLATES LEFT VERY SUBTLE SCRATCHES, AND WHERE THEY OVERLAP, THAT'S WHERE THE DISCOLORATION HAS EMERGED.

SO, THE QUESTION WAS 'WILL THE ARCH BE CLEANED?'

THE NATIONAL PARK SERVICE SAYS FOR RIGHT NOW, NO.

TOO COMPLICATED, TOO EXPENSIVE.

AGAIN, I THINK WE ARE OPEN IN THE LONG-TERM THINKING TO CLEANING BECAUSE WHO KNOWS?

THERE MAY BE A WAY SOMEDAY, BUT... I GUESS WE NEED TO THINK ABOUT HOW THAT COULD EVEN BE DONE.

YOU KNOW, THIS ROPE ACCESS THAT WAS USED TO GET TO THE EXTERIOR IS PERFECT FOR DOING THAT INVESTIGATORY WORK, BUT TO ACTUALLY BE ABLE TO HAVE WORK PLATFORMS THAT PEOPLE CAN WORK FROM TO ACTUALLY CLEAN -- THAT'S SOMETHING THAT WE DON'T KNOW HOW IT WOULD BE DONE.

THIS IS, BY FAR, THE MOST TECHNICALLY CHALLENGING JOB I'VE EVER DONE.

YOU DON'T MIND IF THEY DON'T ASK YOU TO CLEAN IT, THEN?

NO, I'VE GOT SOME IDEAS ON HOW TO CLEAN IT, BUT IT WOULD BE A DAUNTING TASK TO CLEAN IT.

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