All books returned to libraries, which reopen today, will be set aside for about 24 hours before being put back on shelves.

This is part of the effort to keep users safe from the coronavirus, which causes Covid-19.

Responding to queries from The Straits Times yesterday, a National Library Board (NLB) spokesman said the board has also arranged for all high touch points, including book return points and shelves, to be disinfected every two hours, and for hand sanitiser to be placed in all libraries.

He added that NLB referred to guidelines set out by the International Federation of Library Associations and Institutions to come up with its safety measures.

"We will continue to closely monitor the situation and align our book handling practices with evidence-based advisories on this matter," he said.

Books cannot be disinfected in the same manner as most other surfaces owing to their composition.

The United States' Northeast Document Conservation Centre has warned against using liquid disinfectants, powdered cleaners or ultraviolet rays to sterilise books as these methods may damage them. Instead, it recommended a minimum 72-hour quarantine of materials.

Several libraries around the world have also adopted "wait periods", although their durations differ because of the lack of definitive guidelines on the matter.

The Australian Library and Information Association suggested leaving books untouched in a dedicated quarantine area for a 24-hour period prior to handling them, while the Czech authorities recommended a 48-hour period.

But some other libraries, such as those in Denmark, have decided not to implement any wait period.

While the World Health Organisation has not issued any guidelines specifically regarding the reopening of libraries, preliminary results from a study conducted by the Reopening Archives, Libraries and Museums project in the US found that the coronavirus could not be detected on previously contaminated books after three days.

The International News Media Association in March also said that scientific evidence suggests porous paper surfaces are "safe from the coronavirus".

In addition to the measures announced yesterday, NLB had also previously said that all 25 of its libraries, as well as the National Library Building, will be operating, albeit with the shorter hours of 11am to 7pm daily instead of the usual 10am to 9pm.

Only 50 people will be allowed on each floor, and users will be allowed only to borrow and return materials, with newspaper and multimedia stations remaining closed. Patrons will also need to book entry slots online, as libraries will be implementing timed entry to manage the flow of visitors.

Visits will be limited to 30 minutes and visitors can check the real-time crowd conditions online or on the NLB app.