Mathis, et al,
I also support what I believe is the intent behind this TIA, but I have very serious reservations about it as written. Plume is a greater hazard than the inappropriate use of a piped MGVS system on a short term temporary basis, but these systems are in no way designed for or capable of supplying the need for Plume Evacuation as things stand today. (WAGD is a more complicated question all around)
I attach the comment I propose to send in to NFPA as explanation both of the problems I see and the answer I propose. I have also sent this to Chad Beebe in hopes we can modify the TIA and make it something we can vote for, as while I can't see why this is "of an emergency nature", I trust that ASHE has sufficient reasons.
Comments on proposed TIA 1722 and 1723
The proposed TIA seeks to permit the use of Medical Surgical vacuum systems for limited Plume Evacuation applications and when this is done, to ensure that appropriate filtration is provided for these systems.
Understanding the need for this essential occupational safety facility, I am in sympathy with the intent. However, there are three serious objections to this practice:
1. Centrally piped vacuum systems are not sized with this application in mind. This is not because they cannot acheive the required result, but because it is ineconomic to operate a pump to do a job that is far better suited to a fan or blower. Plume evacuation capture devices need high flow but beyond what is needed to acheive that, they are otherwise largely indifferent to vacuum level. Medical vacuum is sensitive to vacuum level, is used and designed for far lower flow rates. The high flow into a medical vacuum inlet needed for Plume evacuation is very likely to reduce the vacuum available to other terminals, very possibly compromising the vacuum level available for surgical applications in that room at least.
While as an temporary measure, use of a medical vacuum terminal for plume evacuation is possible, it would be bad practice to make the medical vacuum a facility's primary plume evacuation resource.
2. It is problematic to draw Plume into the pipeline, as the pipeline is designed and built assuming the system is dry and relatively clean. Plume can leave accumulations in the pipeline at elbows, tees etc. which may over time reduce the pipe Internal diameter. For this reason, it is better practice to filter at the inlet, and prevent the Plume from entering the pipeline at all.
3. The filtration subsystem required for the solution as proposed would need to be sized for the entire flow of the vacuum system. This will mean that the HEPA filtration now provided to reduce emissions from the vacuum exhaust will need to be replaced with a equal number of and potentially larger ULPA filters and activated carbon canisters. Where Plume may be a small fraction of the whole inflow to the system, this would be an undesirable cost for equipment and for maintenance.
This section (5.1.3.7.4) deals with the filters at the central supply system, and therefore does not prevent the smoke from entering the piping. This proposed filtration requirement belongs with the terminal inlet where it will prevent this.
I propose instead:
Leave 5.1.3.7.4 unchanged.
1. Revise 9.3.8 and 9.3.8.1 to read as follows:
9.3.8 Medical Plume (Surgical Smoke) Evacuation and Filtration.
9.3.8.1* Medical plumes (i.e., surgical smoke) generated by the use of energy devices (e.g., electrosurgical units, lasers) during medical and surgical procedures shall be captured as close as possible to the point of generation (i.e. point where the energy device contacts the tissue) by one or a combination of the following methods:
(1)* Dedicated local exhaust ventilation system that discharges in accordance with 9.3.8.2.
(2) Connection and to return or exhaust duct after air cleaning through ULPA and gas phase filtration (e.g., activated carbon).
(3) Point of use surgical smoke evacuator with ULPA and gas phase filtration (e.g., activated carbon) for air cleaning and return to the space.
(4) * Disposal into the centrally piped Medical-surgical vacuum or WAGD systems may be only be used as a temporary expedient provided the gas entering the inlet is first passed through a filtration subsystem including an ULPA filter and gas phase filtration (e.g., activated carbon).
(Note that a definition of an ULPA filter may need to be added)
Add also Annex A 9.3.8.(4)
*A-9.3.8 (4) Centrally piped vacuum systems are not sized with this application in mind. This is not because they cannot acheive the required results, but because it is ineconomic to operate a pump to do a job that is far better suited to a fan or blower. Plume evacuation capture devices need high flow but beyond what is needed to achieve that, they are otherwise largely indifferent to vacuum level. By contrast, Medical vacuum is sensitive to vacuum level and is used and designed at far lower flow rates. Even on a temporary basis, the high flow into a medical vacuum inlet needed for Plume evacuation is very likely to reduce the vacuum available to other terminals, very possibly compromising the vacuum level available for surgical applications in that room at least.
The suitability of a WAGD piping system will vary with the type of system in use. They should be considered suitable only If designed originally to include this use. Otherwise, all the same disqualifications will apply to them as apply to the medical-surgical vacuum.
It is problematic to draw Plume into a vacuum or WAGD pipeline as the pipeline is designed and built under the assumption that the system remains dry and the gas relatively clean. Plume can leave accumulations in the pipeline at elbows, tees, etc. which may over time reduce Internal diameter of the the pipe. For this reason, it is necessary to filter at the inlet, and prevent the Plume from entering the pipeline at all.
While as an temporary measure, use of a medical vacuum or WAGD terminal for plume evacuation is possible, it would be bad practice to make the these a facility's primary plume evacuation resource.
