It may be floating in the serene silence of space, but the International Space Station (ISS) will be so noisy inside that astronauts could miss warning signals and have their hearing damaged.

The clunk and clatter of fans, filters and pumps mean they are likely not to be able to talk, work or sleep properly. The fears are raised in documents obtained by New Scientist magazine.

The first module of the ISS, Zarya, was launched in November 1998. But over a year earlier, the Khrunichev State Research and Production Space Centre in Moscow warned that the noise would result in a "probable worsening of the health of cosmonauts and in unintelligibility of voice communications".

No earplugs

Parts of Zarya will have a perceived noise level of 72.5 decibels and even the quietest areas exceed the space station's design requirements of 50 to 55 decibels.

Space: The only place for quiet?

A Nasa document dated November 1998, states that emergency warning tones would be "minimally audible" in Zarya. Another, dated July 1998, says: "Crew ability to sleep, work, and communicate will be impaired."

A Nasa official responsible for safety on board the ISS, Rich Patrican, responded to the concerns by telling New Scientist: "It will be under control."

He said that Zarya was sent up despite the problems because foam covers could be added later to quieten the noise.

But the sound mufflers will be "minimally effective" according to other NASA documents and Goodman admits he cannot be sure the mufflers will work. Earplugs would risk blocking out alarm signals.

Hearing damage

The Russian service module in which the astronauts will live during construction of the ISS will also be noisy. It is due to launch in September 1999, but in January this year Russian officials said that noise levels will be as high as 74 decibels.

These noise levels would normally be too low to damage hearing. However, the long, constant exposure endured by astronauts on the Mir space station may have had serious consequences.

"There's an indication that a significant number of astronauts have lost hearing in Mir," said Jerry Goodman, who works on the acoustics of the space station. They later recovered a percentage of their hearing loss.