This is an article the I would trot out if anyone tried to argue that a Data Safety and Monitoring Board should, like the investigators, be blinded as to treatment status during their deliberations.
Bradley D. Freeman, Robert L. Danner, Steven M. Banks, and Charles Natanson “Safeguarding Patients in Clinical Trials with High Mortality Rates” American Journal of Respiratory and Critical Care Medicine, Vol. 164, No. 2 (2001), pp. 190-192. doi: 10.1164/ajrccm.164.2.2011028. Available in html format.