A study has found that the risk associated with transmission of airborne particles between spaces on board a cruise ship, through the HVAC system, is exceptionally low.
It also revealed that this was undetectable both in the air and on surfaces.
The independent study was conducted by University of Nebraska Medical Centre (UNMC) and the National Strategic Research Institute (NSRI) on board Royal Caribbean’s ‘Oasis of the Seas’.
It investigated air flow, and particulate matter movement inside the cruise ship and was conducted in July, 2020 in the middle of the global health crisis to evaluate how a cruise ship’s HVAC system worked and what risks were posed to guests and crew.
A team of five medical scientists focused on the effectiveness and efficiency of ship air management strategies – ventilation, filtration and supply – and examined air flow across different areas of the ship, including guest staterooms, crew staterooms, lounges and other public spaces.
They looked at guest staterooms, the casino, ice rink, comedy club, and crew quarters, and released billions of microspheres – simulating SARS-CoV-2 aerosols – in separate locations across the ship.
The microspheres used were spherical particles made of a plastic polymer that are coated with unique DNA bar codes so that they can be easily detected.
No exchange of aerosol particles was observed between spaces only connected by the ventilation system (such as adjacent staterooms, both crew and guest), indicating that the likelihood of aerosol exchange between adjacent rooms was very unlikely.
In public spaces, the casino performed the best, since it has built-in filtering for tobacco smoke. Nonetheless, all venues showed no evidence of aerosol or surface contamination.
In general, particles released in the public areas were not observable after 15 minutes, likely due to dilution in the large spaces.
Based on the report’s findings, Royal Caribbean has adopted some changes to add more protection for those on board.
These included:
- Adjusting shipboard settings to allow for the maximum air changes per hour.
- Incoming air is filtered twice when it comes into the ship, including through a MERV (minimum efficiency reporting value) 13 filter.
- It then travels across the ship through the system to be filtered again in local areas, for example a stateroom or the theatre.
- Upgrading to MERV 13 filters throughout the system.
- Equipped the medical facilities with an independent ventilation system and has added HEPA filters as an additional precaution.
- Ocean air is continuously drawn in from one side of the ship for cooling and ventilation, as the existing air is exhausted on the opposite side of the ship.
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- This constant intake of fresh air, combined with the other robust components of the HVAC system, allows for up to 12 air changes an hour in staterooms and 15-20 changes in public venues.
- This frequency is twice more than what is recommended for land-based public venues by ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers.
The filter MERV rating refers to how much it can filter particles in the air, with a higher number meaning a higher level of filtration. These ratings range between 1 and 20. A MERV rating of 13-16 is considered hospital level air quality.
