Anne Schuchat, principal deputy director at the U.S. CDC, says there is no current evidence to suggest that the coronavirus spreads through air-handling systems. Eric van Dijk, employed at Dutch HVAC specialist Heinen & Hopman, agrees it is unlikely for viruses to spread through a ship’s HVAC system due to the way air travels through the system.

Cruise ship Diamond Princess was quarantined in Japan. The ship had 3700 people on board, of which 620 people were eventually infected by the coronavirus. Some of the passengers expressed worries about the virus spreading through the ship’s HVAC (heating ventilation air-conditioning) system to which the CDC responded.

Filters cannot prevent spread of viruses

According to Van Dijk, whose company did not supply the HVAC system for this ship by the way, ‘fresh air is supplied on a cruise ship by several air handling units. The ducts connected to the air handling units provide the public areas and cabins with fresh air. Within these units, air passes through multiple filters, at least EU4 pleated filters.’ EU4 filters belong to the category of coarse dust filters with an over ninety per cent arrestance.

‘Optionally, these units are equipped with a HEPA (high-efficiency particulate air) filter and/or UV light units to treat polluted air further,’ adds Van Dijk. These filters do not stop viruses from spreading however.

Van Dijk explains: ‘The filtered air that enters a cabin is filtered again in a fan coil unit, but these filters are made to fight bacteria, not viruses. Viruses are so small, that you would need a very strong filter. When you need such a strong filter, your supply air capacity has to be so big that the air handling units are possibly four times as big. This means that the energy consumption and emissions will be many times higher.’ Not something that is desirable for a cruise ship, as these ships already have a name for being polluters and are working hard to lower their environmental footprint.

The system on board the Diamond Princess was supplied by MCI Namirei. In a statement, Diamond Princess’ owner Princess Cruises said ‘the HVAC filtration system on our ships is comparable to those used by land-based hotels, resorts and casinos.’ This probably means this system will also not be able to filter out viruses.

Air routing makes spreading through HVAC unlikely

However, Van Dijk points out the chance of a virus spreading through the HVAC system is still very small. This has to do with the way the air travels. He has drawn the overview below, which shows that, although not impossible, it is unlikely for a virus to travel from cabin A to cabin B.

Text continues under picture.

‘In addition, COVID-19 is expected to spread like flu does,’ says Van Dijk. ‘And flu hardly spreads through air ducts, but through contact and moisture drops (coughing/sneezing). This is unavoidable on a ship with 2000 passengers.’ The CDC has expressed similar findings and has emphasised that staying in a cabin and limiting contact with other people are still the best ways to minimise exposure.

Passengers allowed to leave Diamond Princess

In the meantime, the quarantine measures of the Diamond Princess have been lifted and on Wednesday morning, 19 February, several hundreds of non-infected passengers were allowed to leave the ship. This will continue on Thursday.

Some countries may impose quarantine measures once their compatriots arrive at home. The five Dutchmen on board tested negative for the virus and will not be subjected to such measures.

On Thursday 20 February, Japanese broadcaster NHK reported on the basis of information from the Japanese Ministry of Health that two of the ship’s passengers that were infected, have died. These are the first deaths on the ship. They are a man and a woman over 80 years old.

SWZ|Maritime’s February 2020 issue, to appear next week, contains an article with Heinen & Hopman about smarter climate control on board luxury cruise ships.