Why was this guy spraying this truckload of demolition debris with water?

They’re demolishing Grace United Methodist Church, and yesterday as I drove past, there was a backhoe scooping up loads of broken concrete and stone, and depositing them in a dump truck, which was nearly full. And next to the truck was a hardhatted construction guy carefully directing a firehose of water onto the debris in the truck (not a garden hose–a real firehose).

I formulated three theories as to why this would be, and would like to have one of them confirmed.

  1. To cut down on dust. Hard to imagine that people busily knocking down an immense stone church are concerned about dust after the debris is already in the truck. I’d think they’d want to wet down the demolition site, not the truck.

  2. To cut down the fire hazard. Hard to imagine that a truckload of broken concrete and stone constitutes a spontaneous combustion hazard.

  3. To make the truck and its contents weigh more, because they are possibly being paid by weight for how much they cart away from the site. This seems to me to be the most likely explanation. And yes, I am the most dreadful cynic, why do you ask? :smiley:

Thank you in advance, anyone.

(4) So that the dust in the truck does not blow off the truck as it’s being driven away?

It’s for dust. Any dust created at the construction site itself would be excused by the demolition permit they would have had to get. (Although, if it was excessive or drifting off of the property, they should have been wetting down the debris on site as well.)

Dust drifting off of a moving vehicle off site is a different matter. Particularly if it’s causing a hazard or nuisance to other drivers, the truck driver is just asking to get pulled over and fined. It’s good practice to wet down the load to keep the fines contained, and generally required that the load also be covered with a tarp.

Also, why are you so surprised that they were using a fire hose? Buildings being demolished generally don’t have any garden hose bibs left. Fire hydrants are everywhere. They just have to get permission to use a hydrant from the local Water Department. Sometimes the utility requires that a water meter be added, and the contractor is billed for usage.

As has been said, dust control procedures are included in the permit to destroy the building. It is recognized that in doing so there will be a ceratin amount of unavoidable dust. If it causes actual damage to neighbors they can be compensated for the damage.

However, most communities have ordinances concering dust and debris in loads going to landfills, or anywhere else. Controlling such material from the load is not hard. You either cover the load or spray it with water or both.

And trying to spray the load of a big truck with a garden hose would be an inordinate waste of time.

Oh yes, spraying the load with water doesn’t profit them as you are charged a weight fee at the landfill. The truck is weighed in and out and so you are charged for the water that you have hauled to the dump.

Ohhhhhhhhhhhh. I have been wondering why they’ve been “watering” the construction they’ve been doing on the Northway near the bridge. Every day my car gets a little wet as I pass by. As you can imagine it’s kind of a PITA if I forget to close my windows! But I have been wondering what the heck they were doing.

Is the desire to control dust more of an avoidance of nuisance or real health risk? For example does “watering” a demolition site help prevent any present asbestos from getting into the air?

Before you demolish a building that has or is suspected to have asbestos, you have to conduct an asbestos survey. Any asbestos found then has to be carefully removed in controlled conditions by trained professionals wearing respirators. The whole work area has to be screened off by plastic, and there are controlled entry points with sampling points to ensure that no fibers leave the area.

Only after all of the asbestos is removed can demolition take place.

Asbestos that is fixed in place, as in shingles or floor tiles, do not require such elaborate controls, so long as care is taken not to break the tiles or shingles.

Dust control from other construction debris is for both nuisance control and for health risks. For example, dust from concrete can produce silica dust, which is a health hazard. The elaborate controls necessary for asbestos, however, do not generally extend to silica.

For what it’s worth, all large operations (including construction sites, roadway work, and landfills) have dust control requirements. Dust abatement measures for roadways include large tanker trucks with sprinklers, as well as spreading calcium chloride.

I dabbled with heavy equipment in college, although I was never officially certified (I had enough hours on several pieces of equipment). Aside from being a nuisance and health risk, dust also cuts down on productivity at a job site. For example, grader operators will have to grade slower, so they can see what they’re doing. Much of it can be done by feel, but there are still times where you have to see what’s going on with your blade. Or when using a loader. Sometimes it’s not important how precise you are. Sometimes it is. Dust hinders your ability to properly line up a load.

Wow, thanks all, that was quite informative. :slight_smile: Never thought of “dust blowing off the load”.

I was a bit surprised at the firehose because I was taught as a child that fire hydrants were for “Firemen Only!” and I thought they were “hands off” for the rest of the world. So I wondered if this guy was doing it illicitly, or if he had some kind of papal dispensation, and I wondered what you had to go through to get something like that.

I was kind of surprised to find out as well a few years ago that fire hydrants are used far more by water utilities than by fire departments. The water utilities are also responsible for maintaining and replacing hydrants.

The main concession made to fire departments is that the utility is required to notify emergency services if they are taking a line out of service, and if any hydrants are not operational for some reason, emergency services are notified and the hydrants are bagged so they are not mistaken for operational hydrants.

Water utilities mainly use hydrants for flushing lines. Hydrants are not just installed where needed for fire fighting, they are also installed at stagnant points such as the end of a line. Hydrants are generally flushed annually. It allows any build-up of sediment (including corrosion byproducts) to be flushed out of the line. It also ensures that the hydrant is operational.

Also, as I indicated previously, construction contractors, especially if they are working on a municipal project, often use hydrants if they need a large source of water. They have to get permission, though, and would likely be asked how much water they need. They may be required to install a water meter.

The water utility would be aware of how much water could be spared from its water storage tanks before any fire fighting capacity would be impaired. For any but the smallest utility, you’d have to use a lot of water before significantly affecting the utility.

Some examples of water needs include filling up force main sewers with clean water for pressure testing, filling up water tanker trucks for dust control, filling up sewage wetwells with clean water for pump testing, etc.

As I understand it, new construction sites are water not only to suppress dust, but also to make a nice compact foundation for the building (at least out here, where there is essentially no ground moisture).

In the next neighborhood south of me, when they were tearing up & resurfacing a major street, they also did work on the water & sewage lines underneath it.

So for a few weeks, they put in temporary above-ground plastic pipes that connected to fire hydrants in the next block, and then ran them along sidewalks and connected into individual houses or parts of the water main. This was to continue to supply water to these houses during the construction.

People were told that while the water was chlorinated and perfectly safe, there might be unsightly rust & dirt in the lines when they were first connected. So the homeowners were invited to turn on the taps in the bathtub or sink in their house, and let it run until the water was clear. They were even told that they would have a small credit applied to their water bill to cover this extra water use.

Sometimes I run the fire hose (for dust control and getting dirt in the right state to be compacted) for my dad’s construction company. It’s a much better task than, say, digging with a shovel. And around here, if you don’t keep the dust down, the Dust Police will show up and shut the job down.

Good point. When compacting layers of fill (generally in 12-inch lifts), you often are required to test the degree of compaction with a nuclear density gauge. Generally 95% of the maximum possible compacted density is required, as is a specified moisture content. If the moisture content is too low, you add water. For large areas, a water tanker truck with sprinklers is used.

Whoa, I didn’t know that compaction testing device was radiation-based. I figured it was just a test of how hard it was to pound the stake into it. Intriguing.

Incidentally, I’ve found out the hard way that if you add too much water, the ground becomes impossible to compact and you get in Big Trouble.

Right. You don’t want the moisture content to be too high, either.

Also, nuclear density gauges are the standard method for measuring compacted densities of soil and asphalt. They use a gamma source for density and sometimes a neutron source as well for moisture determination. You need to be certified to operate them, and the paperwork required to store and transport the gauges is a pain as well, so we always subcontract this out.

I have no content to add, but an anecdote:

After they finished the latest round of construction on my street, the utility guys came by to ‘flush out the storm drain’, which I think means they wanted to play with the newly-installed hydrants. :slight_smile:

At any rate, they were out there hooking up hoses and whatnot, and I happen to be standing on my porch staring vacantly in their direction – a habit my wife says I need to stop – when one of them cranked the valve on the hydrant…

…and promptly blew the hose across the street, followed closely by a deluge of water. Which happened to blast a portion of my neighbors newly-installed landscaping bark clear back to his own porch, leaving the plastic ground cover clear. Wet, but clear.

Funniest thing I’ve seen in a while. They turned it off right quick and I don’t think any real damage was done, but I’ll bet that’s a crew that remembers to check the hose connection first for a long time coming. :slight_smile:

I came in this thread too late. I run a smallish water system, and just Tuesday, hooked up a meter to a hydrant for a demolition crew.

I haven’t noticed anything anyone’s said in here to be wrong. My crew is mostly using it for dust control, yes, and I can see that it could be fire supression too. The building going down is a concrete and steel-frame, and could generate sparks against the excavator bucket in the right conditions. Some of the inner components are wood or otherwise flammable, and keeping them damp keeps that risk down too.

The Air Board in California is pretty strict with dust regulations for construction/demolition, and are even starting to enforce them for farmers. Farmers generate an awful lot of dust, but it’s much harder to control. At some construction sites I’ve been on, we’ve had to set up dust monitoring equipment upwind and downwind to prove that we were in compliance.

And I like Sofaspud’s anecdote. I’ve dug a hole or two with the hydrant flow myself, although I try to remember to put a fitting on that redirects the flow. Sometimes you get in a hurry.