Back for the fourth year, the Round Ripon Ultra-Marathon follows the northern section of the Ripon Rowel and is one of the toughest races in the UK, going across a 35 mile course of woodland tracks and open moorland.
Speaking ahead of the race, Simon said: "I have never run anywhere near this distance before so it is going to be an interesting but hopefully enjoyable challenge.
"As a former firefighter, and one who has suffered from a number of years of serious back problems, the Firefighters Charity is one that is very close to my heart and it is a pleasure both to be in a position now where I can actually contemplate running 35 miles and at the same time raising money for such a good cause."
All competitors will be supporting organising charity Teach Africa (www.teach-africa.org) but Simon is also seeking to raise £1,000 for the FFC's efforts to enhance quality of life for serving and retired fire service personnel and their families.
The Charity offers vital support services across the UK for all fire fighters, assisting in excess of 17,500 individuals every year. It costs over £9 million every year to keep the Charity running, and with no government funding, they are completely reliant upon donations and fundraising.
To support Simon, visit his JustGiving page at: www.justgiving.com/simonpaulmarshall