If your work meets the federal definition of research involving human subjects, then written informed consent is required according the regulations. However, under limited circumstances, defined below, the IRB can consider your request for a waiver of consent.
According to 45 CFR 46.116 (d) "An IRB may approve a consent procedure which does not include, or which alters, some or all of the elements of informed consent set forth in this section, or waive the requirements to obtain informed consent provided the IRB finds and documents that:
(1) The research involves no more than minimal risk to the subjects;
(2) The waiver or alteration will not adversely affect the rights and welfare of the subjects;
(3) The research could not practicably be carried out without the waiver or alteration; and
(4) Whenever appropriate, the subjects will be provided with additional pertinent information after participation.