TO: AC Transit Board of Directors
FROM: Michael A. Hursh, General Manager
SUBJECT: Coach Ventilation During COVID-19 Response
BRIEFING ITEM
RECOMMENDED ACTION(S):
Title
Consider receiving a report on positive air flow tests and procedures to ventilate coaches during the COVID-19 response.
Body
STRATEGIC IMPORTANCE:
Goal - Safe and Secure Operations
Initiative - Service Quality
This briefing item provides details of staff’s efforts to promote a safer environment onboard AC Transit vehicles by improving the positive airflow to reduce the amount of exposure to particulates in the cabin space.
BUDGETARY/FISCAL IMPACT:
There are no budgetary or fiscal impacts directly related to this report.
BACKGROUND/RATIONALE:
Various sources have published recommendations for air circulation and ventilation procedures during the COVID-19 pandemic. These recommendations include opening roof hatches and bus windows, therefore, allowing fresh air to enter the cabin.
To have a better understating, District staff collaborated with Safety Committee Members from ATU Local 192 to conduct a practical evaluation. Three tests were developed with a goal to understand how air particulates travel through a bus and to determine the most efficient means of achieving positive air flow on the coach. The process involved discharge of smoke inside the coach to mimic interior cabin air and particulates as the coach was in motion. Various methods to ventilate the coach were deployed at that time. The attributes of the smoke were indicators of how air movement was influenced by the current ventilation method in use.
TEST #1 All windows closed with the Operator’s window open
Creates a vacuum. All smoke moved towards the front of the coach then exited through the driver’s window with full exposure to the operator.
Test #2 Four to six windows opened with the Operator’s window closed
Creates an uncontrolled air environment. Initial air moved towards the rear then circled back towards the front and Operator’s compartment where it collected. Prolonged presence with exposure to Operator and passengers.
TEST #3 All windows closed with rear roof hatch open and air conditioning on
Creates positive pressure with rapid air movement towards the rear roof hatch in a short period of time. The heating, ventilation, and air conditioning (HVAC) system is collecting any onboard air and replacing it with filtered air as the remainder exits through the roof hatch. Smoke eventually dissipated from the cabin.
Positive Air Flow:
• All windows closed, HVAC on, and rear roof hatch open (if equipped).
• The HVAC pulls fresh air into the coach directing it through the ceiling air ducts and creating positive pressure inside which then forces the old inside air out through the roof hatch. This is the most effective way to safely remove interior air.
• To maximize air flow, all windows must be kept closed to maintain positive pressure for ventilation.
• Any open windows disrupt the air flow from the HVAC.
• The HVAC has a capacity to refresh the interior air 50 times per hour.
• The District has buses with rooftop and rear mounted HVAC systems.
• The District has a small number of buses with no rear roof hatch.
The method used to achieve positive air flow is to keep all windows closed, activate the HVAC system, and open the rear roof hatch. This is illustrated in attachment 1, Ventilation.
On August 14, 2020, CyRide, a small transit agency in Iowa published information on an air flow test they conducted on their newsletter CyRide Signals. CyRide provides transportation for the community throughout the city of Ames which includes Iowa State University. AC Transit’s Director of Maintenance reached out to CyRide to understand their testing parameters and was able to speak to Kevin Gries who conducted the test. Kevin confirmed that their method to achieve their goal was to introduce as much fresh air as possible into the bus without any other considerations. The test performed by CyRide doesn’t take in account the risk exposure to the operator or the passengers by airborne particulates due to the air flow introduced to the coach.
Increased Bus Filtration:
• Current fleet in service has been upgraded to MERV7, remainder of fleet to be completed by 9/15.
• Cleaner air inside the bus, captures more particulates than before.
• Filtration media - Highest filtration allowed on our buses by HVAC manufacturer is MERV-7. MERV-7 filters 3.0 to 10.0 Microns at 50%-69%. MERV Rating is the Minimum Efficiency Reporting Value (MERV) for air conditioner furnace filter media as determined by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). Rating scale is from 1 to 16.
Secondary Onboard Air Filtration:
The Director of Maintenance is finalizing his review on emerging technologies available in the market that can be deployed across the fleet to prevent the spread of the virus. The technology using ionization seems to stand out from the rest. Some of the benefits from this type of systems are:
• Can be deployed across multiple bus manufacturers.
• Easy to install.
• Can be transferred to another coach easily.
• Eliminates up to 99% harmful pathogens.
• Effective on Viruses, Bacteria, Mold, Fungus, VOCS, Mildew and Odors.
• High coverage range.
• Safe for passengers and driver.
• Used in the hospital and/or other industries for many years.
The District would like to have this technology available for rollout on the fleet starting January 2021 once approval from the various committees and budget allocation have taken place.
ADVANTAGES/DISADVANTAGES:
The advantage of this coach ventilation procedure will assure maximum positive air flow to expel particulates from the interior of the coach with the least amount of impact and exposure to passengers and the operator.
There are no known disadvantages to this procedure.
ALTERNATIVES ANALYSIS:
No practical alternative to the course of action recommended in this report was identified.
PRIOR RELEVANT BOARD ACTION/POLICIES:
None
ATTACHMENTS:
1. Ventilation
Prepared by:
Tabby Davenport, Safety Manager
Approved/Reviewed by:
Cecil Blandon, Director of Maintenance
Salvador Llamas, Chief Operating Officer