According to questions the customer care team is fielding, many riders are concerned about the circulation and quality of air in the Denver Regional Transportation District's (RTD) light-rail cars.
The Centers for Disease Control and Prevention have stated that key ways to protect individuals and slow the spread of the novel coronavirus include ensuring that ventilation systems operate properly, as well as improving ventilation by increasing the percentage of outside air or total air flow to occupied spaces.
“When considering the COVID-19 pandemic, it is the industry’s understanding that people are less likely to contract the virus when they are in a fresh-air, outside environment,” said Phil Eberl, general superintendent of light-rail vehicle maintenance. “RTD helps emulate that condition inside our rail cars by opening the doors on both sides of the vehicle at every station.”
As RTD’s dedicated team continues to deliver more than 140,000 trips each weekday across the system, the agency says it wanted to provide riders with information about the air they breathe when riding light rail.
The air inside each rail car is fully exchanged every 59 seconds. The ratio of fresh air to recirculated air is about 25 percent versus 75 percent. Every minute, about 750 cubic feet of fresh air enters the passenger compartment with all doors closed. The rail car manufacturer recommends increasing fresh airflow into the rail cars as much as possible.
Recirculated air in RTD vehicles is filtered using two-inch-thick pleated panel air filters at the two return-air grilles on either end of the passenger compartment. RTD changes the air filters inside its rail cars every three weeks. By comparison, it’s recommended that air filters in homes be changed every three months.
These filters carry a minimum efficiency reporting value (MERV) rating of seven or eight, trapping particles down to three microns in size. Such particles include pollen, dust mites and mold. RTD says it does not want to upgrade to a higher-rated MERV filter or an air filter with a higher rating, such as a high-efficiency particulate air (HEPA) filter, which captures viral particles, because they are costly, require a pre-filter or replacement intervals that are too frequent and would slow down the air-flow and air exchange rate.
Eberl added: “Spending millions of dollars on supplemental conditioning systems such as ionization of the air particles or irradiation of the air has not been proven to RTD to provide a healthier environment for our customers during a ride on a light-rail vehicle and thereby do not meet the cost benefit considerations for the investment.”
In the event that the health department issues a serious air quality warning, RTD could allow passengers to use a push button to open each door themselves, which would increase the amount of conditioned air in the passenger compartment while still providing an acceptable air exchange rate.
Like fellow transit agencies across the country, RTD is exploring best practices for cleaning its vehicles and the air inside them. The American Public Transportation Association (APTA) in June published a white paper detailing current industry practices for cleaning and disinfecting transit vehicles and facilities in response to a pandemic. RTD says it is taking many of the measures that are described. In August, the agency began sanitizing vehicles daily with electrostatic sprayers, allowing maintenance workers to sanitize a vehicle with hospital-grade disinfectant in five minutes. The technology provides three times more coverage in the same amount of time than traditional spray bottles, buckets and rags.
Every day, RTD’s light rail maintenance cleaning team cleans and disinfects rail cars, including the floors, step wells, hand railings, hand straps, doors, ceilings and walls.
“The air quality and cleanliness of our vehicles is among the best in the country,” Eberl said. “Our HVAC systems, with the filtering and exchange of the air, are more than adequate to provide a healthy environment for our customers, provided we all follow the pandemic mask and distancing guidelines of the state.”
