The authoritites had been forewarned. The Republican prisoners were confined to their cells - which probably saved their lives. The explosion was hugely too powerful, and brought down not just the prison walls but most of the row of houses opposite the jail, killing at least twelve people.
Some of the outside wall of the jail still stands - along with the chief warder's home, on a street corner and remarkable for having no windows overlooking the street.
Clerkenwell Green just yards away was in the Victorian era a venue for outdoor political meetings, including some held in the aftermath of the explosion by sympathisers with the Fenians - notably a local radical, James Finlen. That created a further public outrage, and Finlen became a figure of notoriety, and eventually was forced to leave London by the hounding of the popular press.