<PAGE>


                                                                      EXHIBIT 3a





                            CERTIFICATE OF AMENDMENT
                                     OF THE
                          CERTIFICATE OF INCORPORATION
                                       OF
                                BHA GROUP, INC.






     BHA Group, Inc., a corporation organized and existing under and by virtue
of the General Corporation Law of the State of Delaware (the "Corporation"),
does hereby certify:

     FIRST: That at a meeting of the Board of Directors of the Corporation,
resolutions were duly adopted setting forth a proposed amendment of the
Certificate of Incorporation of said Corporation, declaring said amendment to be
advisable and directing that the amendment proposed be considered at the next
annual meeting of the stockholders. The resolution setting forth the proposed
amendment is as follows:

          RESOLVED, that the Certificate of Incorporation of the Corporation be
     amended by deleting ARTICLE FIRST in its entirety and adding the following
     new ARTICLE FIRST:

          "FIRST: The name of the Corporation is BHA Group Holdings, Inc."

     SECOND: That thereafter, pursuant to resolution of its Board of
Directors, the annual meeting of the stockholders of the Corporation was duly
called and held, upon notice in accordance with Section 222 of the General
Corporation Law of the State of Delaware, at which meeting the necessary number
of shares as required by statute were voted in favor of the amendment.

     THIRD: That said amendment was duly adopted in accordance with the
provisions of Section 242 of the General Corporation Law of the State of
Delaware.






<PAGE>
<PAGE>


     IN WITNESS WHEREOF, said BHA Group, Inc. has caused this Certificate to be
signed by James E. Lund, its President, and James C. King, its Secretary, this
18th day of February, 1997.


                                    By:         JAMES E. LUND
                                       ------------------------------------
                                           James E. Lund, President



ATTEST:

         JAMES C. KING
----------------------------------
James C. King, Secretary








<PAGE>
<PAGE>




                            CERTIFICATE OF AMENDMENT
                                     OF THE
                          CERTIFICATE OF INCORPORATION
                                       OF
                                PRECIPTECH, INC.






     PRECIPTECH, INC., a corporation organized and existing under and by virtue
of the General Corporation Law of the State of Delaware (the "Corporation"),
does hereby certify:

     FIRST: That by written Consent to Action by the Board of Directors of the
Corporation, resolutions were duly adopted setting forth a proposed amendment of
the Certificate of Incorporation of said Corporation, declaring said amendment
to be advisable and directing that said amendment be submitted to the sole
stockholder of the Corporation. The resolution setting forth the proposed
amendment is as follows:

          RESOLVED, that the Certificate of Incorporation of the Corporation be
     amended by deleting ARTICLE FIRST in its entirety and adding the following
     new ARTICLE FIRST:

          "FIRST: The name of the Corporation is BHA Group, Inc."

     SECOND: That the proposed amendment was submitted to the sole stockholder
of the Corporation for consideration and that the sole stockholder has given
written consent to said amendment in accordance with the provisions of Section
228 of the General Corporation Law of the State of Delaware.

     THIRD: That said amendment was duly adopted in accordance with the
provisions of Sections 242 and 228 of the General Corporation Law of the State
of Delaware.






<PAGE>
<PAGE>


     IN WITNESS WHEREOF, said PRECIPTECH, INC. has caused this Certificate to be
signed by James E. Lund, its President, and James C. King, its Secretary, this
18th day of February, 1997.


                                    By:         JAMES E. LUND
                                       ------------------------------------
                                           James E. Lund, President



ATTEST:

         JAMES C. KING
----------------------------------
James C. King, Secretary


<PAGE>