Dust Control Safety on Demolition Sites

When working with toxic substances like asbestos, PPE is required, but other emissions can be controlled at the source. (PHOTO: BossTek)

Outdoor airborne dust used to have a simple solution: require workers to wear an N95 mask or respirator. Easy, right?

However, that doesn’t take into consideration several factors such as proper use of the mask, correct and consistent upkeep, and monitoring usage. Not that masks are a bad solution – they’re called Personal Protective Equipment (PPE) for a reason – but they just don’t address the presence of airborne particulate emissions as a serious regulatory violation.

When regulators from the Occupational Safety and Health Administration (OSHA) attach a Personal Dust Monitor to a worker, they are measuring exposure, regardless of whether a mask is worn or not.

Generally, inspectors are looking for Respirable Crystalline Silica (RCS) particulate matter (PM) smaller than 10 microns (µm) in size at less than 50 micrograms (µg) in weight over an 8-hour time-weighted average (TWA), i.e., a single shift.

Once measured, inspectors usually order violators to address air quality, regardless of personal protective equipment.

This is why preventing dust emissions at the source is more desirable than passive protection such as masks. More and more, regulators are identifying atomized mist as their preferred method for airborne dust control.

This is why preventing dust emissions at the source is more desirable than passive protection such as masks. More and more, regulators are identifying atomized mist as their preferred method for airborne dust control.

The Consequences of Dust

RCS is invisible to the naked eye and is the cause of silicosis and pneumoconiosis, the main chronic lung diseases found in, construction workers, miners and other bulk handling industry employees.

The substance has also been linked to kidney disease, acute pneumonia, lung cancer and even serious mental decline. Research published in 2019 in the Life Sciences Journal concluded that the exposure of healthy subjects to ambient PM affects the brain, causing inflammation and memory loss.

An OSHA violation can be accompanied by fines and -- in some extreme cases – operational closures until a viable solution is implemented. Reported cases of dust related health issues tied to workplace operations could be followed by increased scrutiny, higher health insurance premiums or even lack of coverage.

Once airborne dust passes the site line, the Environmental Protection Agency (EPA) takes over and serious permit violations can dramatically affect operations.

A DustBoss DB-60 unit in operation on site. (PHOTO: BossTek)

Violations can also impact the availability and cost of future permits, depending on operators’ ability to demonstrate that they have taken serious steps to address particulate emissions, such as the addition of a mist cannon to their equipment portfolio.

Controlling Airborne Dust

Currently, the only viable method for controlling airborne outdoor dust emissions is using water. To effectively control fugitive particulates, water droplets must be approximately equal in size to the particles.

One reason is that the droplets must be small enough to travel with particles on the same ambient currents and collide with them. If droplets are too large, then the “slipstream effect” comes into play, and those collisions are less frequent. Small droplet size is one of the primary reasons why atomized mist is preferred by bulk handlers over hoses or sprinklers.

Hoses typically create water droplets 200 - 10,000 µm in size as compared to atomized mist, which ranges from 50 – 200 µm. Larger than 200 µm, droplets are unable to linger in the air or collide with dust particles.

Due to their mass, they fall and form air currents around them. Like wind traveling around an airplane wing giving it lift, large droplets cause the same slipstream effect.

When the tiny particles encounter the larger droplets, they get caught in the air draft around the drops, which diverts them away rather than being absorbed. However, when a particulate collides with an atomized droplet, their combined mass drives both to the ground.

Atomized mist cannons are automated machines that are placed, turned on, and left alone. The largest sized cannon will use a maximum of 39 gpm to cover an area of up to 5 football fields when using the 359º oscillator. In addition to safely providing airborne dust control, cannons also reduce the labor costs of operation over that of hoses with significantly less runoff.

How Does A Misting Cannon Work?

Industrial mist cannons (aka, “fog cannons” or “dust cannons”) employ a cone-shaped barrel with atomizing nozzles in the front and a powerful fan in the back, protected by a mesh safety grate.

A DustBoss DB-60 unit in operation on site. (PHOTO: BossTek)

They can be direct-wired or powered by a generator set. Water is usually supplied by a 1.5 in. (38.10 mm) hose with a cam-and-groove quick disconnect (sizes may vary depending on the size of the equipment and the available water sources).

Water is run through an in-line 30 mesh 595 micron filter system to remove impurities that can clog nozzles, then to a booster pump to increase pressure – which is why the cannon only initially requires 10PSI (0.69 BAR) of constant water pressure to operate.

The flow is pumped to a brass or stainless steel manifold with as many as 38 nucleating nozzles, which fracture the water into a fine atomized mist.

Atomized mist cannons are automated machines that are placed, turned on, and left alone. The largest sized cannon will use a maximum of 39 gpm to cover an area of up to 5 football fields when using the 359º oscillator.

In addition to safely providing airborne dust control, cannons also reduce the labor costs of operation over that of hoses with significantly less runoff.

What Atomized Mist Cannon Is Right For My Site?

To improve the safety on any site, operators must first understand the application and the source of the dust. These seem like no brainers, but working with coal, shale, and other hydrophobic materials may require a surfactant water additive and a dosing pump.

A hydrophobic substance will repel water, causing it to bead and roll off, but the surfactant causes the water to spread across the substance. This can not only benefit the airborne capture of particulates but also cause clumping in stockpiles which can further suppress emissions from wind or disruption by equipment.

For safety, take into account:

Mobility – Many operators need to adjust machines for a myriad of reasons: task switching, varying wind direction, different sites, etc. Consider the needs of the application and choose a model mounted on a wheeled cart or skid where appropriate.

Versatility – Some cannons have varying spray options for differing wind conditions or access to high-reach places.

Proximity to power sources – Mounted on a mobile carriage, some cannons come with diesel gensets that power them through an entire shift and beyond.

Source of dust – Some outdoor/indoor storage areas are static and have many sources of dust. Disruption from front loading or reclaiming causes dust. Loading from a stacker conveyor or tripper conveyor are also sources. Whether inside or outside, tower-mounted cannons cover a wide area and reach high above stockpiles. Specially designed misting heads address localized conveyor dust.

Wind – Wind can be a concern for atomized mist, but bulk handlers have found that positioning machines upwind allows the mist to travel with dust particles. During windy conditions, both mobility and versatility are essential qualities that should be considered.

If the application is frequently exposed to winds, then some pressurized options should be considered. Although fan driven atomized mist has a long reach, it can be affected by high winds. To extend to tall areas – such as high-reach cranes performing demolition – consider pressurized atomized dust control options like the DustBoss Surge.

Dust and Safety in the Workplace

Most employers will agree that the health and welfare of their employees is paramount. No matter the size of the site, a dust management plan can be implemented using a wide variety of methods, including mist cannons.

After an environmental assessment has been done, consider bringing in a dust control expert who can help create a dust management plan geared toward compliance, health, and the safety of workers.

New approaches to dust suppression Latest innovations tackle dust emissions