By Stephen Beech via SWNS
The best way cruise ships can stop the spread of viruses such as COVID-19 is to blast the cabin with the air-con for 12 minutes.
They found that simply more ventilation did not mean safer cabin conditions for passengers and crew.
In fact, more ventilation could spread infected droplets five times further.
But pumping up the air con in cabins for 12 minutes after passengers disembark leaves the air inside “completely refreshed” for the next occupants.
The research team came up with an “optimum” ventilation plan that reduces energy consumption and improves passenger comfort.
The Covid pandemic had a serious effect on cruise ships when it began to spread around the world.
Cruise ship passengers became disproportionately infected and many were stranded on board to quarantine.
Focus since has been directed at addressing the need for improved ventilation on cruise ships – since dispersing fresh air in cabins and other enclosed spaces is critical for mitigating viral spread.
A group of researchers from Cyprus looked at how ventilation can affect transmission of airborne viruses in a typical cruise ship cabin based on guidelines developed before and after the pandemic.
Study author Professor Dimitris Drikakis said: “The most recent standards and regulations on room safety regarding the airborne transmission of viruses focus on high rates of air exchange.
“But this can be inefficient in terms of energy consumption, can compromise passenger comfort as it generates strong air drafts, and most importantly, can spread saliva droplets up to five times more when passengers cough.”
Drikakis and his team conducted simulations for virus droplets from a cough in a regular cruise ship cabin that accommodates two or more people, with different ventilation rates and different positions of the person emitting the cough.
Computational fluid dynamics testing ranged from 1.5 to 15 air changes per hour (ACH) to capture all possible scenarios, from minimal ventilation to rates exceeding the most recent recommendations.
Drikakis, of the University of Nicosia, said: “The study reveals that a higher ventilation rate is not the best strategy to avoid spreading airborne diseases.
“Complete evaporation of the saliva droplets may not necessarily mean all viruses or bacteria become instantly inactive.
“Therefore, we should aim at minimum droplet spreading inside the cabin and different ventilation strategies for occupied cabins.”
After analyzing the results, published in the journal Physics of Fluids, the researchers determined the ideal use of ventilation systems to operate at medium flow rates of around 3 ACH when a cabin is occupied, to increase to 15 ACH for at least 12 minutes after it has been vacated.
They say that, in that way, the air would be completely refreshed for the next occupants.
They also recommend the same minimum time of 12 minutes as a “clearance wait time” for similar-sized rooms with a minimum of 15 ACH.
Drikakis said: “Our main argument for the proposed values is the necessity to minimise droplet spreading while maintaining good ventilation levels, comfort and energy consumption.”
He added: “Keeping ventilation at the proposed values reduces energy consumption and improves passenger comfort in contrast to the use of higher ventilation rates.”
