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The Green Files

By Michael Halliwell
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Michael Halliwell

The Green Files by Michael Halliwell

Michael Halliwell, M.Eng., CESA, EP, P.Eng., is an Associate and Environmental Engineer for Thurber Engineering Ltd. in Edmonton, Alberta, Canada. During his 13 years with the company, he has been involved with environmental site assessment, remediation, construction inspection and supervision, and project management. He also performs hazardous building material assessments for asbestos and lead paint.

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Friday, January 31, 2014

The Hidden Hazards of Bridge Rehab

Any time that one is working bridge rehabilitation, there are certain hazards that should be pretty obvious.

The first, and often foremost, is falls and fall hazards.

But there are other potential hazards at bridge rehabilitation jobs that may not be quite so obvious—and can be missed, to the worker's peril.

Hidden Hazard 1:  Lead Paint

For painted spans, this should be a fairly obvious hazard.

However, a recent experience on the rehabilitation of a local, near-100-year-old bridge showed that this is not always the case.

CSX Transportation Bridge
Courtesy David Garvin via The Rural Blog

Sometimes, lead paint is obvious, as happened when CSX Corp. finally agreed to strip the coating from its peeling Barren River bridge in 2011. But lead can also hide.

The owner had a local occupational health firm check the bridge for lead. Initially, a portable x-ray fluorescence (XRF) analyzer was used to check the bridge.

The U.S. Housing and Urban Development (HUD) guideline for a positive finding of lead-based paint was 0.5% by atomic absorption analysis or 1.0 mg/cm2 by XRF. Of the 23 locations sampled by XRF on this old bridge, however, not a single one came back with a positive lead result.

Nevertheless, because of the bridge's age and the likelihood of many coats of paint having been applied, a second testing technique was performed.

Bulk samples were obtained from many of the same locations tested by XRF. And this time, they returned multiple elevated results, including one that exceeded the guideline.

Soil sampling around the bridge confirmed that encountering lead was a possibility. The soil samples had elevated lead content, suggesting that past maintenance activities (blasting fallout in preparation for re-coating or, possibly, overspray from the re-coating itself) had released lead from the bridge to the soil near the abutments.

Lesson learned: Field kits and field instruments are great tools, but they are not perfect.

CSX Bridge
Courtesy David Garvin via The Rural Blog

Field kits and field instruments may not always reveal lead buried under generations of coating layers. Especially with old bridges, additional testing may be required.

If there is any doubt about the lead content of the paint (or multiple layers of paint) involved, don’t be afraid to dig deeper and send bulk samples to the lab.

Hidden Hazard 2: Asbestos

Another local bridge was recently upgraded with a new deck and wider sidewalks. In this case, the existing deck and walkways were concrete, with several utility conduits within the walkway slabs.

The plan was pretty straightforward: Remove the utilities, break up the sidewalks and deck, put on the new sidewalk supports, and start forming for the new deck and walkways.

Unfortunately, however, the utility conduits proved a complicating factor: They were asbestos cement pipe.

So, the plan was modified to saw-cut the conduit out and keep it encapsulated in the surrounding concrete. A series of vertical and horizontal cuts was planned to separate the three conduits and remove them (still contained in the surrounding concrete) in segments, which could then be loaded by zoom-boom into a bin for off-site disposal.

In addition, the saw-cutting into segments would be done with extra water to keep the dust to a minimum, and workers would be kept from the cutting area as much as possible to limit potential exposure.

Unfortunately, the concrete cutting didn’t work as expected.

Ultimately, the contractor made the choice to use the same set-up (track hoe with concrete breaker) that was being used for the deck removal to get the sidewalks and conduits removed. The following picture shows how well the asbestos cement pipe survived this approach:

Backhoe-on-asbestos
Michael Halliwell

Although there was run-off from the concrete program keeping the area moist in this picture, the abatement wasn’t ideal. Asbestos cement pipe debris remained in place long after the cutting was complete, allowing equipment to run it over when dry.

It doesn’t matter whether the asbestos is in cement pipe, conduit insulation, gaskets or another component; the removal of asbestos-containing products needs to be treated as an abatement and taken seriously.

One exposure won’t kill immediately, like solvents or gases can. But it can take as little as one exposure to cause serious and permanent health effects later in life.

Hidden Hazard 3: Silica

The recent unveiling of newly proposed silica guidelines in the U.S. has a lot of companies and individuals in construction discussing exposure.

For concrete bridges, this should also be an obvious hazard: Exposure to silica dust can occur while cutting, grinding or grit-blasting concrete. We protect workers in these cases from the potential of high-concentration exposures.

But have you ever thought about potential emissions of silica dust from other sources?

Silica dust can be generated when jack-hammering concrete; when cleaning up (i.e. sweeping concrete debris or dried cutting slurry and using the air gun to “dust off”); when spreading crushed materials; or even when moving around bags of cement or sand.

Abrasive blasting
OSHA

In sloping terrain with poor ventilation, abrasive blasting produces excessive levels of silica-containing dust. The dust exposure obscures the view.

This doesn’t mean that workers need respiratory protection all the time. Rather, we need to be aware of potential secondary exposures and take appropriate steps (i.e. not letting slurry dry out, using misting / wetting to control dust generation) to minimize them.

Overall, the industry has come a long way in identifying the major hazards involved with bridge rehabilitation and exposures to substances like lead, asbestos and silica.

But by being aware of some of the other possible exposure routes, there is a potential to protect ourselves and others on the job just that little bit better.




More items for Health & Safety
   

Tagged categories: Asbestos; Health and safety; Lead; Lead generation; Overcoating lead; Paint and coatings removal; Painting Contractor; Respirators; Silica; Thurber Engineering Ltd.; Ventilation

Comment from Damian Schimminger, (2/3/2014, 8:13 AM)

OSHA publishes, the number one method for lowering exposures to these hazards is to use a substitute solution. The use of Sponge Jet abrasives would greatly reduce worker exposure and fugitive emissions. For more in depth analysis contact Sponge Jet Inc., www.spongejet.com or (603)-610-7950.


Comment from M. Halliwell, (2/3/2014, 10:45 AM)

A very similar steel bridge (similar age and only a couple bends upstream) was done with water blasting. With a washing already planned to try to remove some of the salts, the containment was already water tight. Made for a bit of a win-win: didn't have to worry about grit penetration of the containment, no dust generation, less waste generation (no lead contaminated grit to deal with) and the same gear was usable for both operations (though at much lower pressure for the washing).


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