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Spit Threatens Busy Calcutta Bridge

Monday, January 10, 2011

What’s eating Calcutta’s famed Howrah Bridge? Spit.

The steel bridge’s 78 steel hangers are being rapidly, dangerously corroded by spit laced with gutkha, a sweetened type of chewing tobacco that has become a national obsession, officials say.

The thickness of the steel hoods protecting the hangers has eroded from six millimeters to an average of just three millimeters since 2007, when all of the hanger-base covers were replaced. The hangers were also fully recoated and restored in 2005.

That rate of deterioration has officials concerned for the bridge’s safety.

Left: http://howrahbridgekolkata.nic.in; Right: The Telegraph

The hangers were fully recoated and restored in 2005 (left), but have lost an average of three millimeters of surface steel since then (right).

‘Giant Spittoon’

Some of that is due to normal weathering and some to vegetable and human waste, officials say. But most—by far—is due to the tons of gutkha-laced spit unloaded on the bridge every day from more than 100,000 drivers and 500,000 pedestrians. Newspapers say the local populace uses the bridge as a “giant spittoon.”

Spitters are regularly fined, but bridge officials say they do not have the resources to make a meaningful dent in the practice.

“Gutkha contains highly corrosive elements that erode even steel,” a senior port trust official told The Telegraph newspaper on Sunday (Jan. 9).

“A safety audit is now being planned to find out the effect of constant spitting and several other factors on the stability of the hangers that transfer the load of traffic uniformly across the structure.”

As Corrosive as Acid

Accumulation of gutkha-laced spit has the same effect on steel as acid would, forensic sciences expert Biswanath Kahali told the newspaper. The result is a serious threat to the bridge’s structural integrity.

“Slaked lime combined with catechu and tannin, which are all components of gutkha, form an organic compound that acts as a corrosive agent on a steel surface. In combination, these substances can gradually corrode a steel structure,” added Kahali.

Focus on Fiberglass

Because regular recoating (the last complete repaint used 26,500 liters of paint) and patch painting have not worked, officials of the Calcutta Port Trust are turning to fiberglass armor.

Trust officials have commissioned a company to develop a prototype fiberglass hood that would cover the base of the pillars. The threat is urgent; officials want the prototype within a month.

http://howrahbridgekolata.nic.in.

Repainting the bridge last took more than 26,500 liters of paint.

The hood is expected to be a two-piece cover with an interlocking system. Fiberglass is less likely to be damaged than steel, and the detachable cover can be cleaned, officials say.

Port officials are also planning a new study of the bridge to examine the extent of corrosion, assess stress levels and density of traffic, and recommend a maintenance procedure.

Bridge Crashes

Aggravating the bridge’s decline is terrible driving in the area. More than 20 vehicles have rammed into the bridge since 2008, when surveillance cameras were installed, The Telegraph reported.

The Howrah was the world’s fourth cantilever bridge when it opened in 1943. The central span over the Hooghly River is 1,500 feet long. The 23,500-ton steel bridge is 86 feet wide; 15 feet of that is used for pedestrians.

Fire Engulfs Cables

The bridge’s fortunes suffered another setback Saturday (Jan. 8) morning, when fire broke out and engulfed the cable wires atop the bridge, sparking a panic. A preliminary investigation focused on a short circuit as a cause of the sudden fire, which spread rapidly, although no one was injured.

Comment from Steve Badenhop, (1/11/2011, 2:05 AM)

Rather than spending all of that money on custom glass armor, why not just coat it with a spray-applied product like Rhino Lining or a similar product? It's chemical resistant and a lot more durable. The fiberglass sounds like yet another exotic solution to a problem than could have been solved with more simplistic means.

Comment from S Mukherjee, (1/11/2011, 7:27 AM)

Use mica-filled vinyl ester or novolac vinyl ester (take off all zinc). Can be applied by brush, roller or spray. It will provide lasting solution to the problem. Simple solution to spit problem.

Comment from Tom Schwerdt, (1/11/2011, 8:09 AM)

Interesting that painting it used roughly one liter of paint per ton of steel - given usual wastage, the number would be even closer.

Comment from remko tas, (1/11/2011, 10:08 AM)

Dirt built up behind the detachable cover may increase corrosion. The spit will slide down and damage lower sections of the structure. Adequate spit resistant coatings are the solution.

Comment from remko tas, (1/11/2011, 10:12 AM)

The painters' work setup is a relief compared to current safety regulations!

Comment from DANIEL COSTANTINI, (1/11/2011, 8:41 PM)

Pressure wash, 2 coats mastic, and urethane should easily hold up to that type of environment. Who knows what type of surface prep and paint application occurred then? It sounds if it had been painted recently as 2003, there is an inspection problem. Their saliva and tobacco juice cannot compare to a Cleveland winter with road salts and various other chemical contaminants.