You are often having to work around other traffic movements. In the instance of a rail bridge you often have to work around other train movements. In the incidence of a road bridge you have to work when the traffic flow is lower, so that means working at night. Working at night brings its own challenges because it means that suddenly you’ve got a large visibility issue, so you need to figure out excellent lighting; helmet lighting, stand lighting, hanging lighting, nozzle lighting, anything to be able to increase visibility and make sure you get a good, thoroughly prepared surface and also a consistent quality coating application. The other challenges around train movements is you have to stay around their schedules. If a train comes through and you are applying containment, because of the fact that trucks and trains create a turbulence issue, meaning the sprayed out coating will be damaged by "dry spray". The containment system has to be very well attached to the scaffolding structure, otherwise it can be ripped off the scaffold. Often train drivers are weary and don’t see the slowdown signs and so trains can come through at very short notice, creating quite a major safety risk. It is not uncommon to hear of railway bridge projects where the operators can be exposed to hazards such as train movements as a consequence of poor communication or misunderstanding regarding site access.
Another consideration are the distances to be found in projects such as these...You may be working on a bridge that could be a mile long and you may have to operate off a barge, accessing that barge in the middle of the river. Sending the blasting, abrasive and compressed air out into the middle of the bridge you have complex access arrangements, scaffolds, and containment. It can often get very hot and humid inside, so you may need dehumidification and cooling. You may need motor boats to access your barges. You need to make sure that you don’t get any hazardous coatings falling into the rivers and waterways. Typically a lot of bridges have hazardous coatings, e.g. lead paint, so you need specialized personnel on site, certain qualifications to do the work, soil testing, blood testing and air testing. You need very thorough documentation for the whole process and you also need to protect your workers with decontamination trailers and wash facilities.
You also need to think about the weight loading of the bridge, are you adding extra weight to the bridge; the wind loading on the bridge when you contain it. You need to think about when you’re designing the containment size, how much you can blast and paint in that day. If the containment is too big you are not going to be able to provide enough extraction. You need to provide the right amount of extraction in a hazardous coating area of 100ft per minute in the case of lead paint, which means you need to have your containment size around your dust collector size. Correctly sizing the duct work to run to the contained area is also a challenge. You may need to run multiple ducts, you may need to run larger than standard size ducts. You need to have good quality duct work so that it doesn’t collapse under the suction pressure. There are a lot of challenges about understanding containment, conveying abrasive over long distances, vacuuming abrasive over long distances and you need to make sure your guys don’t get dehydrated. There are a lot of things to be thinking about on a bridge project.