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Design Ventilation Flow Rates for Blasting Containments: Who Decides?

TUESDAY, AUGUST 1, 2017

By Kevin Guth


More items for Environmental Controls

We have all seen boilerplate project specifications over the years. Some standard specification provisions are still quite valuable after many years of use, but others have outlasted their usefulness. One recurring standard provision I see quite often that fits into this category is specifying a design ventilation flow rate for field industrial containment structures.

There are potential risks associated with specifying design ventilation flow rates that outweigh the benefit of their inclusion in the project specification. There is a better way to achieve the desired result of protecting the workers, the public and the environment.

Background

In 1993, the OSHA Lead in Construction (29 CFR 1926.62) standard ushered in many fundamental changes to how industrial structures were rehabilitated.

In part, as a response to the above cited OSHA standard, the interim SSPC Guide 6, Guide for Containing Surface Preparation Debris Generated During Paint Removal Operations, established suggested minimum air flow rates within a containment system as a way for project designers and contractors to demonstrate the implementation of feasible engineering controls. SSPC turned to a well-established industrial hygiene publication from the American Conference of Governmental Industrial Hygienists (ACGIH) to address this issue: Industrial Ventilation, A Manual of Recommended Practice. It was a prudent first step.

Containment
Images courtesy of the author

There are potential risks associated with specifying design ventilation flow rates that outweigh the benefit of their inclusion in the project specification.

As a result, the abrasive blasting and painting industry adopted the air flow of 60 feet per minute (fpm) down draft and 100 fpm from the ACGIH publication because field practice at the time demonstrated this was a sound course of action. Years later, SSPC removed the suggested design air flow rates from the standard and placed the information in the notes section of SSPC Guide 6, while still requiring minimum specified airflow rates be established for class 1A and 2A containment classifications.

Current Practice

Some departments of transportation and other owners continue to list design containment ventilation air flow rates (60 fpm down-draft and 100 fpm cross-draft) in their specifications. These flow rates are often established in specifications without consideration of the project-specific parameters.

SSPC Guide 6 gives an excellent explanation of what should be considered when designing an effective engineering control:

  • Blasting pressure;
  • Number and size of blast nozzles;
  • Type, size and friability of abrasive;
  • Flow rate of abrasive;
  • The lead or toxic metal content;
  • Thickness and age of the paint being removed;
  • The type and size of the structure being prepared; and
  • Configuration of the containment system being installed.

While 60 fpm to 100 fpm air flow rates may be effective velocities for many projects, these rates are not effective for all projects. A review of the literature, and my observations as a practicing certified industrial hygienist, performing industrial hygiene air sampling and ventilation readings in field containments for over 20 years, indicate there is not a one-size-fits-all approach to addressing this issue. There is no silver bullet design air flow rate that will work in all cases—making the establishment of a specified design air flow rate problematic.

Why Specify?

If there is no guarantee that the specified velocity will be effective in establishing a feasible control, why specify a design air flow rate? Moreover, how prudent is it to have a specified air flow rate, if the project-specific conditions have not been considered? Establishing a standard design air flow rate feels arbitrary—though I know SSPC had good reason to move in that direction. I have heard a few explanations from some owners and project design consulting engineers why they continue to specify design air flow rates. To my surprise, their responses have not had anything to do with establishing feasible engineering controls.

Bridge project

There are too many variables associated with specifying air flow rates within a containment structure for a project designer/owner to consider and quantify—especially when each contractor has their unique way of approaching the containment and ventilation system.

Some consulting engineers argue that design air flow rates are intended to serve as a mechanism to decrease the size of an active abrasive blasting and painting containment for quality control reasons and for wind load considerations on bridges.

On the face of it, these seem like reasonable explanations. However, these issues can be addressed by other means—without invoking design air flow rates.

Specifying a design air flow rate could end up costing the owner or their project designers money and expose them to unnecessary risk. After all, the burden of implementing a feasible engineering control is one the contractor should bear. Designing and implementing effective control methods appears to fall into the contractor’s means and methods category.

Specs and a Project Gone South

What if a contractor had instituted adequate control methods, employee exposures were acceptable, visible emissions and accumulations met the project requirements and biological monitoring indicated low blood lead levels, but the achieved specified design flow rate had not been met? Should a contractor’s failure to meet the design air flow be deemed a contract non-conformance? I was once involved in a project where this scenario played out. The owner insisted the contractor meet the contract design air flow rate—even though their control methods were working as intended.

The project did not conclude on a happy note. In the end, the disagreement in the interpretation of the design air flow rate cost both sides a lot of money.

Potential Negative Consequence

Suppose a contractor’s employee is (lead) poisoned. The contractor followed the owner-specified ventilation flow rate within containment while using proper PPE and all other recommended control methods. A smart plaintiff’s attorney could make the case that the contractor performed his work within OSHA requirements and designed its containment in accordance with the prescribed air flow rates found in the project specification.

The contractor could assert that they assumed the design flow rates were in the specification because they were sufficient to protect the contractor’s employees from over-exposure to lead. It is not unreasonable to believe this is a possible outcome. One argument made against this scenario is that the design flow rates are intended to be “minimums.” Yet, I have rarely seen the term “minimum” appear in a specification in terms of a design flow rate. Moreover, from the contractor’s perspective, does the word “minimum” not imply the specified air flow rate is the minimum necessary to achieve compliance? Regardless of one’s opinion on this argument, why muddy the waters when it is not necessary? These situations can be avoided by taking a different approach.

Solution

The ultimate goal is to protect the employees performing the work, the public and the environment from adverse impact. Instead of specifying design air flow rates, target velocities should be proposed in the contractor’s containment and ventilation design plan submittal. This plan should be developed by a professional engineer experienced in industrial ventilation systems who has considered the site-specific parameters of the project.

Bridge project

The specifier should allow the contractor the opportunity to demonstrate that the contractor proposed air velocity inside containment will provide the necessary and desired controls.

There are too many variables associated with specifying air flow rates within a containment structure for a project designer/owner to consider and quantify—especially when each contractor has their unique way of approaching the containment and ventilation system. It is not a sound course of action to default to a specified air flow rate without a compelling reason.

Measuring Operational Outcomes

The specifier should allow the contractor the opportunity to demonstrate that the contractor proposed air velocity inside containment will provide the necessary and desired controls. This can be accomplished by providing acceptance criteria in the project specification for the performance of the mechanical ventilation system in reducing worker exposures, controlling blood lead levels and controlling emissions. Approval of the containment and ventilation design should be contingent upon the successful implementation and verification in the field. I have seen this approach work on numerous large-scale hazardous paint removal projects with success.

Specification Considerations

Below are a several items to consider when writing a specification that addresses a field containment structure and ventilation system. This is not intended to be a complete list of things to consider.

  • Require the contractor to retain a professional engineer to design and seal the containment and ventilation system.
     
  • Require the professional engineer be qualified in industrial ventilation systems.
     
  • Require the professional engineer visit the project site and confirm the containment and ventilation system has been installed in accordance with the designed and sealed containment and ventilation plan.
     
  • Require the designed engineering controls reduce airborne exposures to levels as low as feasible.
     
  • Require instrument verification of negative pressure.
     
  • Require the contractor provide routine checks of the mechanical ventilation system in order to ensure effective and continued performance.
     
  • Establish wind load requirements.
     
  • If necessary, limit the size of a containment based on the project specific requirements—not on air flows.

Specifying industrial ventilation flow rates offers very little value to the owner and may result in unneeded project costs; in fact, it opens up the possibility of more issues rather than providing any solutions. If owners/designers want to limit the size of field containments, it should be done without invoking design air flow rates.

ABOUT THE BLOGGER

Kevin Guth

Kevin is serving as the Principal for KGC, where he oversees all aspects of business and technical operations. For the past 21 years he has provided senior oversight and management of KGC’s most complex industrial hygiene and hazardous waste management projects. Kevin holds a Master of Science in Public Health (Specialty: Industrial Hygiene) from the Tulane School of Public Health and Tropical Medicine and is currently pursuing his Doctorate in Public Health (Specialty: Occupational Health) from the University of South Florida. He is a Certified Industrial Hygienist (CIH) and certified Project Management Professional (PMP).

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Tagged categories: Abrasive blasting; Air quality; Containment; Health and safety; Specification; Surface preparation; Ventilation

Comment from Michael Beitzel, (8/3/2017, 2:03 PM)

Much of what we do in the way of containment is a hold over from the early 1990's when regulations were initially passed. We have learned much along the way and It is long past time that we revisit and refine measures on lead removal projects that are cost reducing that can be taken while still assuring safety of the workers, public, and the environment.


Comment from Paul Tsourous, (8/3/2017, 3:12 PM)

Kevin, the article is a well written insight into the ventilation requirements. In our experiance airflow requirements very often fail to correlate to exposures to personnel within containment. Existing coatings of structures for blast cleaning often have wide varying levels of heavy metals which is one of the primary factors influencing exposure levels. The standard downdraft/crossdraft flows do not address this, nor do they address the number of blast nozzles simultaneously creating the level. When we have tried to submit calculated exposure limits by addressing factors such as high lead based paint in existing coatings, number of blaster, etc to develop a more practical true no of air changes bridge owners have always rejected this even though it would be a more accurate prediction of personnel exposures. All they want to see is airflow speeds. Thanks again for the nice blog.


Comment from Doan Thang, (8/4/2017, 5:57 AM)

Thanks Kevin. The new technology of ventilation like Push-Pull could hep to reduce the air change ratio with the same effective. Airflow speed makes sense at dust generation source. Out of that area, it wastes of money.


Comment from Bryan Swartz, (8/4/2017, 9:54 AM)

I agree 100% with the fact that the word "minimum" is not often used and should be. Why only use the minimum crossdraft/downdraft figures. It gives the workers a false sense of security if the 60 fpm or the 100 fpm is only used when those figures should actually be higher due the a higher lead content or more blasters. Good read.


Comment from Kevin Guth, (8/4/2017, 2:33 PM)

Thank you, Paul. I agree with you. The site-specific parameters of the job have to be taken into consideration when designing an effective ventilation control and should hold more weight than a specified air flow rate.


Comment from Thomas Van Hooser, (8/7/2017, 9:14 AM)

Very interesting and informative article. Well done.


Comment from Anthony Kavouris, (8/7/2017, 10:38 AM)

Well Done. Containment ventilation is effected by all the factors that you talk about. When determining what works, what doesn't, what is best and what is not, I think we have to stay focused on the basics. The ACGIH air flow rates were based from working in a booth, and the dynamics of working in the field are altogether different than working in a booth. The safety of the worker, the environment outside of the containment, and the safety of the job is what's important. High exposure is part of our industry and effective engineering controls, PPE, Hygiene, training and knowledge is what works, and a lot of times 100 fpm Horizontal and 60 fpm Vertical have nothing to do with it.


Comment from Jerrod (Jake) McCann, (8/8/2017, 11:11 AM)

Good article Kevin, I absolutely agree it’s time to move forward. It’s embarrassing that the industry would allow this initial offering to remain largely unchanged when from inception there was never a standard for the measurement of parameters imposed. As one can see from the photo’s you chose for your article, the variables from one containment system to another are to vast for one size fits all air flow rates. Honestly, it’s lazy and negligent on behalf of specifiers when due diligence should include principles of ALARA (as low as reasonably achievable) when health and safety is concerned. Performance based designs develop innovation and effective innovation supports reduction (both in cost and exposures).


Comment from M. Halliwell, (8/8/2017, 12:06 PM)

Well written entry, Kevin. I think many of the commenters here note that minimums and old regs haven't kept pace with exposure control and industrial hygiene changes over the years. Unfortunately, with the way OSHA and the bureaucracy works, it'll be a decade or two before there is an update. Hopefully those dealing with containments will move toward due diligence (doing what they reasonably should do/ what a reasonable contractor would be expected to) rather than de minimus (the absolute least they can possibly get away with to meet a spec or old guideline) when it comes to exposure of their workers.


Comment from Tom Schwerdt, (8/31/2017, 2:30 PM)

I would suggest that experts here become involved in a rewrite of Guide 6.


Comment from Kevin Guth, (8/31/2017, 3:50 PM)

Tom: I do not believe a rewrite of Guide 6 is in order. In fact, target air velocities were placed in the notes section of the guide many years ago; yet the 100 fpm cross-draft and 60 fpm down draft velocities continue to show up in project specifications. Given the many site- specific variables associated with designing an effective engineering control, makes establishing a flow rate for a one size fits all problematic. My point was simply for designers/owners to consider the site specific parameters in their design. Satisfactory field performance is the goal.


Comment from Noel Stampfli, (9/5/2017, 2:03 PM)

Good article. In fact the only one I have ever seen on the subject. Kudos for jumping into this can of worms. Years ago I noted the velocities proscribed in Guide 6 and recognized that they were for a blast booth which indeed is only remotely relatable to a containment structure on a bridge. Looking at the articles recommendations I note that several suggest that containment ventilation be designed by a P.E. presumably in the employ of the contractor. First question is what standards are used to base such a design upon before the fact: minimum air changes, velocity, visibility, contaminant concentration? After that, what criteria should be used by an owner to accept or reject such a design? Sounds like you are proposing that containment be treated similarly to scaffold or excavation safety where there are statutory requirements to have design by P.E.'s. In those cases, engineers have a clear set of criteria to rely on. Codes proscribe live loads and wind velocities on scaffolding, including containments, and soil pressures on shoring are well understood. Similarly, it would seem that some minimum standards should be proscribed for containment with some clarity. Designing engineering controls to reduce airborne exposures to levels as low as feasible begs the question of what is considered feasible. Small containments and giant dust collectors are neither warranted or feasible all the time. A contactor on a large scale painting project will have a different perspective about feasibility than say an owner or their CIH. I would argue that feasible would be that level at which there is adequate ventilation to ensure that contaminant concentration is below the point at which the appropriate PPE becomes ineffective. Isnt that pretty much what OSHA is about? Without grinding around too much on this perhaps it is reasonable to suggest a reasonable minimum number of air changes and a minimum velocity. That will at least get the equipment and containment sized reasonably. Compliance with OSHA is based more on monitoring and PPE and it is not necessary to duplicate that. I am with Tom Schwerdt on this one: Guide 6 should be improved to address the concerns you have pointed out. Perhaps all it will take is to introduce the appropriate caveats about including the velocity in a project specification.


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