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Properly Ventilating Enclosed Blasting and Painting Jobsites

4 PRINCIPLES and 3 RULES OF EFFECTIVE BLASTING VENTILATION

 

Unfortunately, many contractors consider ventilation to simply be a compliance cost when in truth VENTILATION PAYS FOR ITSELF VIA A SAFER AND MORE PRODUCTIVE ENVIRONMENT.  We offer these principles and guidelines to assist in the health, safety, and productivity of your workforce.

4 PRINCIPLES:

  1. Good ventilation helps maintain air quality within the breathing zone of an operator down to a point that allows the operator’s respirator to effectively deal with any remaining atmospheric contaminants.
  2. Good ventilation helps maintain Good Visibility by extracting dust and allowing lighting to illuminate the work area.
  3. Good ventilation brings in fresh air to dilute any contaminants in the work area preventing it from reaching an explosive level. Always use gas monitors.
  4. Good ventilation also protects against noxious dust or lead contaminants escaping the blasting enclosure and polluting the external environment.

 

3 RULES to follow when designing your ventilation system:

  1. Air should be brought in high – and extracted low. The reason for this is two-fold:
    • First, solvent fumes and dust are heavier than air. High to low extraction uses gravity to assist in their removal, and
    • This helps limit the exposure of these contaminants in the breathing zone of the operators. Ventilating upward will naturally lift contaminants and increase the odds of compromising PPE equipment and/or the vision of operators.
  2. The system needs to deliver the correct air flow to achieve the correct number of air changes (MEASURED IN CHANGES PER HOUR OR AIR VELOCITY THROUGH THE WORK AREA) – and this depends on the following three factors:
    • Type of contaminants being discharged
    • Type of work
    • Size of space
  3. Hazardous dust or fumes need to be properly captured or exhausted safely to comply with environmental or OSHA regulations.
    • If work area is encapsulated the cross-sectional area should be as small as possible.

Design Considerations For Containment And Ventilation

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HOW TO EFFECTIVELY VENTILATE A TANK WITH A SINGLE MANHOLE OPENING AT THE TOP?

Obviously, due to the set-up, Principles 1-3 are naturally compromised.  And this scenario is quite common in the industry.

Here is a work-around we recommend.  But again, this tip is general information – please confirm with an expert before implementing this strategy on your project.

  • Use a duct saddle that employs a pinched funnel-style section to prevent obstructing the manhole. The saddle duct should allow workers the ability to enter and exit the manhole without difficulty.
  • Then, make sure the ducting is long enough to run from the manhole to the lowest possible point of a far back corner within the tank. If coating the tank string a cable from the manhole to an attachment at the far corner, and clip the ducting to the cable to keep it off the floor

What’s the most common mistake we see in the field?

  • Often the ducting only extends slightly into the tank, below the mouth of the manhole, into the upper regions:
    • When the ventilation method employs positive pressure (blowing air) – it simply circulates the dust and vapors due to a constant downward pressure.  Some dust will exit but concentration of dust will build.
    • When the ventilation method employs negative pressure (vacuum extraction) – the ducting, although effective in the uppermost levels of the tank, isn’t effectively drawing the heavy dust and gases that gravity concentrates toward the bottom of the tank.
  • However, if the ducting is taken to a far back corner, the ducting effectively draws dust away from the operators and extracts the air through the ducting in the instance of vacuum extraction.

POORLY IMPLEMENTED VENTILATION

It's common to see ducting barely extend beyond the tanks opening. For either process (positive or negative pressure) this is a highly ineffective set-up.

PROPERLY IMPLEMENTED VENTILATION

Extending the ducting to the far back corner, and using negative pressure (vacuum extraction) is the best set-up for this particular scenario.

Again, these suggestions are general work-around tactics giving you an overview of how to mediate dust in a single entrance tank project.  However, we strongly suggest seeking an experienced specialist to assist in your specific situation.

Should you have any concerns or questions regarding a painting project you have coming up give our service representatives a call.  We’re always here to help!

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