Grit blasting is a process of cleaning metals and other surfaces with a material in a high-pressure blast. Material is thrown against a surface to remove contaminants. If the material used is silica sand, the process is known as sandblasting. Using abrasives other than silica such as aluminium oxide (corundum), glass particles, polymeric particles and even particles from organic waste such as the shells of some nuts, the technique is called grit blasting.
Sandblasting or grit blasting in plants consists of the use of a pressurized jet that spreads through the air and grains of sand or grit to eliminate deformations or stains in materials such as concrete or metals.
Both techniques are used in processes for cleaning surfaces of different materials. It is a technique that allows us to achieve very good results. At the same time, it is necessary to comply with a series of safety measures to avoid accidents, since its use poses a risk to the operators and nearby people.
Safety at work is very important. In recent years, occupational risk prevention has evolved a lot and both employers and workers are increasingly aware of it. Accidents at work are very common, therefore, we must do what is necessary to reduce them. Grit blasting in the industry is dangerous if the necessary prevention measures are not used. Sometimes, we tend to not worry about these situations, but it should not be like that, what is at stake is our health.
Grit blasting vs sandblasting
On many occasions, the terms blasting, sandblasting and grit blasting are confused when we refer to the surface treatment process by abrasive impact. Occasionally these processes are considered synonymous but they are different processes and terms.
When we talk about these terms we are always referring to the treatment of surfaces by the impact of abrasive particles thanks to the action of compressed air and using a gun. The term sandblasting is old since currently, it is not possible to use silica sand because it is a prohibited abrasive for producing silicosis (currently other types of abrasives are used such as silicates, microspheres, corundum, etc…)
Truth be told, “Sand” blasting is now a bit of a misnomer. The abrasive blasting industry rarely uses sand as a treatment medium because sand has certain properties that make it difficult to work with. There are much better and safer blasting materials on the market today than silica sand. They include media made from minerals, metals, glass, plastics, and organics like corn cobs and walnut shells.
Grit blasting hazards
Grit blasting or sandblasting has the potential risk of dust inhalation and high noise exposure. More than 2 million US workers are potentially exposed to dust containing crystalline silica. Prolonged inhalation of silica-containing dust exposes these workers to the risk of contracting a disease known as silicosis—a nodular fibrosis of the lungs that causes breathing difficulties. More than 100,000 American workers are engaged in high-risk activities, such as sandblasting operations. Most of these operators work in construction.
When performing air blast abrasive surface cleaning, you have to deal with various risks to your health and safety. Some of these risks can be lethal, so you must understand what they are and observe proper safety precautions. The hazards of grit blasting include, but are not limited to: dust, noise, and equipment.
Dust inhalation
Dust results from the breakdown of abrasives and the spraying of surface coatings, rust, mill scale and other materials onto the steel surface. Individual dust particles range in size from 1 micron (1/25,000 inches) to 1,000 microns (1/25 inches) in diameter. Dust greater than 10 microns may be visible and settle quickly.
Dust smaller than 10 microns, called respirable dust, is invisible, remains suspended in the air for a longer period, and can pass through the defences of the respiratory system and settle in the small air sacs in the lungs called alveoli.
Dust of this size cannot be dissolved by lung fluids because the lung cannot break down or flush out the particles, it makes the next best thing in its defence program which is to isolate the intruder by building a thick, thick tissue. When too much of this tissue develops, the lung is said to be “fibrotic,” or in a condition of fibrosis.
The routes of entry and their associated health effects depend on the chemical and physical properties of the dust. If the dust is soluble in water and respirable in size, it can enter the alveoli, pass through the alveoli walls in the lungs, and enter the bloodstream. Once in the bloodstream, the dust can be rapidly transported through the body and damage various organ systems.
Toxic metal exposure
Other health hazards may be present in the dust produced by the grit blasting process. These hazards can result from the removal of coatings that contain toxic metals such as lead, arsenic, cadmium, and hexavalent chromium.
One of the most dangerous toxic metals found in system coating removal is lead, a toxic metal that can damage the formation of the blood, nervous, urinary, and reproductive systems. Lead also accumulates in the body; therefore, exposure to small doses over long periods can cause great harm.
Metals such as hexavalent chromium can irritate the skin or cause an allergic reaction. Other metals can have an irritant effect on the respiratory tract, such as pulmonary edema (fluid buildup in the lungs) caused by severe exposure to cadmium dust. Entry can occur through ingestion, usually caused by poor hygiene practices such as eating, drinking, and smoking in the work area.
To determine the specific toxic metals likely to be present in system coatings, paint chip samples should be collected from representative areas of the structure. The metals whose samples must be analyzed would depend on a series of considerations such as the type of structure and the type of coating system to be evaluated.
Sometimes the toxic metal content can be determined based on historical knowledge of the coating system being evaluated. Toxic metals can also be present in virgin abrasive blasting media, such as crystalline silica in silica abrasive grit. However, dust containing crystalline silica can also be produced during other abrasive blasting activities, such as concrete surface preparation.
Hose rupture or de-attach
A very useful element is the whip check that links the hoses joined by couplings during grit blasting. Whiplash arrestors allow the hoses to remain linked in the event of any failure of the coupling and rupture and not move in the form of a dangerous whip.
Shock due to static electricity
At the time of deploying the grit blasting hoses between the sandblasting pot and the nozzle, the first check must be carried out of earthing. Shocks often lead to severe injuries to the operators, as well as much more serious accidents such as falls.
High noise exposure
Not using adequate protection can lead to permanent hearing loss.
What is silicosis?
There are several types of silica. For example, quartz is a crystalline form of silica and is the most common mineral in the Earth’s crust. When rock containing quartz is chipped, hammered, drilled, crushed, loaded, transported or unloaded, small particles of silica escape into the air and can be inhaled by workers.
Silica sand containing quartz is used in pressure washers to clean surfaces. Some of the surfaces that are cleaned through this process are the exteriors of buildings and bridges and the interiors of storage tanks and pipes. The silica sand used during the sandblasting process breaks down into fine particles that remain suspended in the air.
If these particles are small enough to be inhaled deep into the lungs, they are known as respirable crystalline silica. Inhalation of these fine silica particles causes more damage to the lungs than inhalation of larger particles. This process causes rapid and severe forms of silicosis in sandblaster operators.
Accelerated Silicosis —Silicosis contracted 5 to 10 years after being exposed to high concentrations of crystalline silica.
Acute Silicosis —Silicosis with symptoms that can develop from a few weeks to up to 5 years after exposure to very high concentrations of crystalline silica. The term “acute” usually refers to a short but severe illness. In the case of acute silicosis, the time between exposure and severe illness is shorter than in accelerated or chronic silicosis.
Chronic Silicosis —Silicosis contracted after 10 years or more of exposure to low concentrations of crystalline silica.
Fibrosis —scarring in the lungs caused by breathing in hazardous dust or chemicals such as crystalline silica. As the disease is acquired, the lungs begin to stiffen and become less flexible, and breathing becomes more difficult.
Sand and grit blasting safety
To select the appropriate type of protective equipment to be used by the operators involved both in grit blasting activity in enclosed areas (blasting rooms) and open area works, it is advisable to previously define the different work areas involved in the work, the same ones being following:
- Primary zone: it is called the zone closest to the surface to be grit blasted and it is requested because it is in contact with the jet and rebound of the abrasive used with a high level of pollution. The work carried out inside a blasting room is always considered work in the primary area.
- Secondary Zone: this surrounds the primary zone, being an area where there is high pollution but a low risk of receiving projected abrasive.
- Tertiary Zone: it is characterized by having admissible levels of pollution and no risk of being in contact with the projected abrasive.
In sandblasting or grit blasting jobs, operators are subjected to several potential risks, some of them directly related to the task itself (pollution, rebound of the abrasive with the piece to be grit blasted and the direct blast of the abrasive) and others related to all work that is carried out on-site or in industrial processes (high noise levels, blows, etc.)
Personnel working within the secondary area must be protected against pollution using respirators, not requiring the use of protection against abrasive blasting. The need for protection against abrasive blasting is obvious, considering that the particles are projected at more than 300 km/h, but protection against pollution is even riskier.
Since it is never convenient to breathe any type of dust, and in In the case of using sand, free silica can be breathed in, responsible for an irreversible process disease; silicosis.
It should also be considered that many times, the dust produced by the removed paint is extremely harmful or directly toxic, as in the case of lead-based paints. In sandblasting or grit blasting tasks, face masks are inefficient because they do not comply with the two protections required for the operation.
It is extremely important (mandatory in the USA) to use remote control, the dead man system. This system allows the control of the equipment from the projection nozzle and interrupts the projection of air and abrasive if the operator releases the hose or the trigger.
Sandblaster safety
The air that reaches the operator must be suitably filtered, suitable for human respiration and with a maximum of 10 ppm of carbon monoxide at a flow rate of approximately 0.5 m3/min. Lower flow rates can allow the entry of dust particles and higher flow rates cause eye irritation.
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The most widespread is a filter specially designed for human respiration, which receives air from the compressor equipment and sends it to the positive pressure protection equipment. Filtering this air requires retaining particles larger than 25µ, oil and water aerosols. Also, deodorize it to make it pleasant to breathe. These filters do not remove carbon monoxide and it is advisable to install a CO alarm in the airline.
It is preferable to have a small air compressor, which is free of oil to feed this type of filter. However, the most usual is to use the same compressor that is used to drive the abrasive. There is a high potential risk here because these compressors are usually lubricated and the emission of CO due to excess lubrication or overheating is very feasible. In these cases, a CO alarm should always be used in the breathing airline.
- It must be taken into account that grit blasting involves a significant physical load for the person who performs it. For this reason, breaks of between 5 and 10 minutes are recommended every 25 or 30 minutes of work in those cases in which the operator controls the lance and the hose directly. During this rest time, the worker must remain in a dust-free space to remove respiratory protection.
- Respiratory protection equipment must be used, which is a continuous flow compressed air line, which will be attached to a suit or a helmet that has a resistant visor, and a layer that covers both the shoulders and the chest.
- While the jet is being used, there should only be one person in the work area to avoid accidental projection onto another worker. Of course, the area must be away from an area where people are concentrated. To this, we must add adequate signage in the workspace.
- Personal hygiene is also essential as a safety measure. Operators should wash in a nearby available toilet space before eating, drinking or smoking. 10 minutes of cleaning is recommended before leaving the workplace.
An accepted requirement for human breathing air is as follows;
- Oxygen from 19.5% to 23.5%
- Condensed oil MAX 5 µg/m3
- Carbon monoxide MAX 10 ppm
- Carbon dioxide MAX 1000ppm
Finally, the operators must work at less than 80dB for an average work of 8 hours a day. This makes it necessary to always use ear protectors for blasting operators and support personnel.
What PPE is required for grit blasting?
Basic equipment for operator protection for sandblasting or grit blasting tasks is made up of the following elements:
- CE class positive pressure helmet built with materials resistant to abrasion and easily replaceable, with internal air circulation
- Anti-drowning air conduction tube with noise attenuator
- Filter suitable for human respiration with a disposable cartridge
- Protection gloves.
- A frontal leather protective suit
- Safety boots
Employer responsibilities
Use abrasive blasting materials that are less hazardous than those containing more than 1% crystalline silica. Because substitute abrasives can also have toxic effects, NIOSH recommends the use of proper engineering controls, work practices, and respiratory protection for all abrasive blasting operations, regardless of the type of abrasive used.
- Recognize situations where dust can be generated, and plan to remove dust at its point of origin.
- Inform workers about their exposure to dust, the possible health effects and the risk of silicosis.
- Perform air monitoring to measure worker exposure and verify controls are working properly.
- Provide training to workers in safe work practices to reduce exposure to dust and high noise.
- Post warning signs to mark the boundaries of work areas that may be contaminated with respirable dust.
- Provide workers with Safety Data Sheets (SDS) for silica, masonry products, alternative abrasives, and other hazardous materials to which they may be exposed.
- Provide workers with information on the safe handling, labelling, and storage of abrasive materials.
- Equip workers with appropriate respiratory protection systems, including NIOSH-certified respirators, and a respiratory protection program to ensure proper use and maintenance of respirators.
- Conduct regular medical examinations of workers who may be exposed to respirable dust and high noise.
- Provide disposable protective
- Provide areas where workers can shower, change, and put on clean clothing before leaving the workplace. This practice prevents contamination of other work areas, cars, and homes.
Worker and supervisor responsibilities
- Use appropriate respiratory protection and other PPE, provided by the employer.
- Remove dust from equipment with a water hose instead of using compressed air. Use vacuum cleaners with HEPA filters. Use practices like wet sweeping instead of dry sweeping.
- Put on disposable protective clothing in the workplace.
- Shower and change into clean clothing before leaving the workplace to avoid contaminating other work areas, cars, and homes.
- Do not eat, drink or use tobacco products or cosmetics in work areas.
- Wash hands and face before eating, drinking, or smoking outside of work areas.
- Maintain proper communication with the blaster.
- Maintain frequent housekeeping.
- Maintain proper hose management to avoid trip hazards.
- Cover the area with tarpaulin to prevent dust propagation.
Conclusion by muniriyathse (safety zone)
- Training: Ensure all workers involved are fully trained on the safe operation of sandblasting equipment and the potential hazards.
- Personal Protective Equipment (PPE): Provide and require the use of appropriate PPE for all personnel in and around the blasting area.
- Engineering Controls: Implement ventilation systems, dust suppression techniques, and containment booths to minimize exposure to dust and fumes.
- Work Practices: Establish safe work procedures, including pre-blast inspections, communication protocols, and emergency response plans.
- Environmental Considerations: Take measures to prevent the spread of dust and contaminants to the surrounding environment.
