Article:The line will carry people from the roof of St Thomas' Hospital on South Bank to Victoria Gardens, beside the Houses of Parliament.
Twenty people who pledge £50,000 or more will be able to use the crossing when it runs for one day on 2 December.
The money raised will be donated to Evelina London Children's Hospital.
People harnessed to the 463m wire will travel head first at speeds of up to 40mph (64kmh).
It will be built by 30 specialist firefighters over three days.
LFB Deputy Assistant Commissioner Andy Roe said he came up with the idea "to thank the remarkable [hospital] staff" after they treated his nine-year-old son Zaki.
He said: "I realised that I could use my specialist skills to rig up a zip wire from the roof of the hospital."
Evelina London is trying to race £2.7m to build a Clinical Research Facility.
Head of Evelina Hospital's allergy service, Prof Gideon Lack, said the proposed facility would "help find better treatments and cures".
The LFB is also running a competition for one person to win a place to ride on the zip wire.

A summary of the above article is?
The first zip wire to cross the River Thames will be set up by the London Fire Brigade (LFB) to raise £1m for a children's hospital.