I thought that the building was on fire for a quite a long time, so even if a fire brigade arrived at the place, it would be not likely to put out this fire.
I thought that the building was on fire for a quite a long time, so even if a fire brigade arrived at the place, it would be not likely to put out this fire. Then say eg . . . so help was not very likely to succeed.
If you just say help was not likely, it means help is unlikely to occur.