Autonomous Abrasive Blasting Robot

A robot that can perform blasting operations autonomously without exposing workers to health and safety risks from using blasting equipment and being in the blasting environment.

Description:

Using sand or alternative abrasives to clean, texture or abrade concrete, masonry or painted surfaces generates large amounts of dust which may contain high levels of contaminants that may include crystalline silica, lead or other hazardous chemicals, and creates a hazard for everyone in the vicinity.  An autonomous abrasive blasting robot is an engineering control that automatically performs blasting operations after it scans and 3D maps the surface areas to be blast cleaned.  Therefore, this robot eliminates potential worker exposures to airborne contaminants, noise, and confined space, as well struck-by safety hazards associated with traditional abrasive blasting.

An autonomous abrasive blasting robot, such as the SABRE Alpha1 (figure 1), is a robotic arm that operates on a six degree of freedom axis.  The arm contains an image sensor that first generates a 3D map of the surface.  Those spatial data are then calculated with other parameters (blasting speed, nozzle distance from the surface, nozzle angle to the surface and the blast stream overlap) to automatically provide an optimum blasting trajectory for the job.  Then, the operator checks to make sure the area is clear and sets the safety switch before the robot starts blasting.


Figure 1. Setting up the SABRE Alpha1 in a storage tank (Photo courtesy of Sabre Autonomous Solutions)

The SABRE autonomous abrasive blasting robot is constructed with a lightweight chassis and guide rails weighing less than 25 kilograms (approximately 55 pounds).  While abrasive blasting jobs can vary, the optimum distance is approximately 2 feet using a No 7 (7/16-inch) nozzel at an operating pressure of 110 pounds per square inch.  The mounting platform, stationary or mobile, is determined after the application is identified.  The manufacturer SABRE Autonomous Solutions can provide design options on how to mount the Alpha1.  Alternatively, users can customize their own mounting platform following the guidance diagram of the base plate mounting holes (figure 2).


Figure 2.  SABRE Alpha1's base plate (Photo courtesy of Sabre Autonomous Solutions)

Risks Addressed:

Abrasive blasting is also known as sandblasting since silica sand is commonly used as the abrasive.  Crystalline silica dust exposure may cause silicosis or lung scarring with prolonged exposure. Silicosis is an incurable, progressive, sometimes fatal, disease. OSHA has a Permissible Exposure Limit for exposure to respirable crystalline silica (RCS) of 50 micrograms per cubic meter of air (µg/m3) as an 8-hour time weighted average. RCS exposure has also been associated with lung cancer, kidney disease, autoimmune disorders, and chronic obstructive pulmonary disease.

Occupational exposure to lead comes primarily from inhalation and ingestion of lead dust and fumes. Construction tasks with the highest potential for exposure to lead include abrasive blasting of lead-painted surfaces, welding, and torch cutting. Workers sometimes unintentionally bring lead dust home on their clothing, which can pose a hazard to family members. Children are especially susceptible to lead poisoning. When effective engineering controls are not available, it is important to wear protective clothing and other personal protective equipment, change your clothes and shoes before getting home or entering your car, and launder all lead-contaminated clothing separately.

Operating blasting equipment can be very loud.  During abrasive blasting, high noise levels can originate from the abrasive discharge nozzle, the impact of abrasive on the substrate, and the noise generated from the blasting equipment.  Repeated overexposure to noise causes permanent hearing loss and ringing in the ears (tinnitus).

Working in confined spaces, such as abrasive cleaning inside storage tanks, can present some conditions that can be immediately dangerous to life or health (IDLH).  A confined space is any enclosed area not designed for continuous human occupancy that has a limited or restricted means of entry or exit.  In a confined space, existing ventilation is not sufficient to ensure that the space is free of a hazardous atmosphere, oxygen deficiency, or other potential hazards.

Finally, struck by flying object hazards can also occur when using compressed air, which is commonly used to power tools and clean surfaces.  A struck by flying object hazard occurs when something has been thrown, hurled, or propelled across space.

How Risks are Reduced:

Traditional abrasive blasting requires the utilization of blasting equipment at a proximity that can expose workers to health risks from silica, lead, and noise exposures as well as fast-moving flying particles. The autonomous abrasive blasting robot described here eliminates the need for workers to manually operate traditional abrasive blasting equipment and be present in the environment where the blasting is taking place. Workers would first position the ALPHA1 to automatically plan the robotic motions using its 3D scanner. A 3D view of the environment is then generated allowing for the preview of planned motions and the monitoring progress at a distance safe exposure to safety and health hazards.  Furthermore, the ALPHA 1 is small enough to be installed in areas with restricted access.

While there have been no published studies on the risk reduction of using an autonomous abrasive blasting robot, a similar study has shown an automated blasting tool, such as the Pittman Vacuum Blasting System, to effectively remove and contain lead-based paint during blasting operation (Echt et al, 2000).  Another study described the need to use robotic abrasive blasters to minimize unhealthy working conditions for operators stripping ship hulls as they are subject to environments of high-speed sand particles bouncing off of surfaces, paint and other toxic materials being stripped, and high noise levels (Souto et al., 2012).

Effects on Productivity:

Productivity is increased when using the SABRE ALPHA1 over traditional abrasive blasting and remote-controlled abrasive blasters.  Per the manufacturer SABRE, "once grit blasting commences, the air is quickly filled with dust, significantly reducing visibility, meaning that remote control of a robot by the grit blaster is [also] not an option, so an autonomous solution is required."  The ALPHA1 can also work in low-lighting conditions and reducing the need for breaks to let the dust settle during a blasting operation.

Additional Considerations:

The use of water-based controls may result in wet and slippery ground and walking surfaces. During cold weather this may lead to the formation of ice and an increased risk of slips, trips and falls. Debris and abrasive blasting media that are not removed from the work area while wet may become airborne once dried, posing an inhalation hazard to anyone in the area. Maintain a work area free of debris and excess water to reduce the risk of these hazards.

The use of water as a dust control increases the risk of shock when electricity is used in the same area. Electrical cords and extensions must be rated for the tool's power requirements, be regularly inspected, replaced when damaged, and used in combination with ground fault interrupt circuits.
 
The use of gasoline-powered equipment poses the risk of carbon monoxide exposure, particularly in areas where airflow is reduced. Steps to control exposure are important because the gas is invisible, odorless and tasteless. Poisoning by carbon monoxide can occur quickly indoors, but working outdoors does not ensure operators won’t be overcome. Small, inexpensive personal monitors should be worn by the operator to warn of unacceptable exposures.
 
As is the case with any construction equipment, users should follow manufacturer safety recommendations and comply with any applicable local, state or federal regulations.  When blasting lead painted surfaces or where environmental regulations requires spent abrasive be disposed of as hazardous waste for any reason, wet blasting may complicate disposal and require containment of runoff water.

Contributors:

Jean Christophe Le, MPH, Bruce Lippy, Ph.D. - CPWR The Center for Construction Research and Training
Alan Echt, MPH, DrPH - National Institute for Occupational Safety and Health