Document:

<PAGE>
                                                                   Exhibit 10.43

                       FIFTH AMENDMENT TO CREDIT AGREEMENT

     This FIFTH AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is made as of
the 27th day of March, 2002 by and among CECO GROUP, INC., CECO FILTERS,
INC., AIR PURATOR CORPORATION, NEW BUSCH CO., INC., THE KIRK & BLUM
MANUFACTURING COMPANY, KBD/TECHNIC, INC. and CECO ABATEMENT SYSTEMS, INC. (the
"Borrowers"), and PNC BANK, NATIONAL ASSOCIATION ("PNC"), individually and as
agent for itself and the other banks (collectively, the "Banks") which from time
to time are parties to the hereinafter defined Credit Agreement (in such
capacity, the "Agent").

                                   BACKGROUND

    A.    The Agent, the Banks and the Borrowers are parties to a Credit
Agreement dated as of December 7, 1999 as amended by Amendment to Credit
Agreement, dated as of March 28, 2000, by Second Amendment to Credit Agreement
dated as of November 10, 2000, by Third Amendment to Credit Agreement dated as
of March 30, 2001 and by Fourth Amendment to Credit Agreement dated as of August
20, 2001(as amended, the "Credit Agreement").

    B.    The Borrowers have requested and the Agent and the Banks have agreed
to amend the Credit Agreement on the terms and conditions set forth herein.

    NOW, THEREFORE, in consideration of the foregoing and for good and valuable
consideration, the legality and sufficiency of which are hereby acknowledged,
the parties hereto, intending to be legally bound hereby, agree as follows:

    1.    Definitions.  Capitalized terms used herein and not otherwise
defined herein shall have the meanings assigned to them in the Credit Agreement.

    2.    Amendments to Credit Agreement.  The Credit Agreement is hereby
amended as follows:

    (a) The provision in paragraph 2(m) of the Third Amendment to Credit
Agreement (as modified by paragraph 2(h) of the Fourth Amendment to Credit
Agreement), which modifies Section 6.1(a) Leverage Ratio of the Credit
Agreement, is hereby modified as follows:

        (m) Section 6.1(a) Leverage Ratio of the Credit Agreement shall be
    abated as it presently exists through January 1, 2002 and shall be modified
    as follows:

        (a) Leverage Ratio. Permit the Leverage Ratio, as of the end of any
        fiscal quarter ending during the period specified below, for the prior
        four consecutive fiscal quarters, to equal or exceed the amount set
        forth opposite such period:

                                       1

<PAGE>

<TABLE>
<CAPTION>
            ---------------------------------------------------------------------------------------
                                                                     Leverage Ratio Must Not Be
              Last Day of Fiscal Quarter During Period                       Greater Than
            ---------------------------------------------------------------------------------------
              <S>                                                   <C>

            ---------------------------------------------------------------------------------------
              December 31, 2000 through March 30, 2001                        5.50 to 1
            ---------------------------------------------------------------------------------------
              March 31, 2001 through June 29, 2001                            6.30 to 1
            ---------------------------------------------------------------------------------------
              June 30, 2001 through September 29, 2001                        6.70 to 1
            ---------------------------------------------------------------------------------------
              September 30, 2001 through December 30, 2001                    5.50 to 1
            ---------------------------------------------------------------------------------------
              December 31, 2001                                               3.40 to 1
            ---------------------------------------------------------------------------------------
</TABLE>

              provided, however, the abatement of Section 6.1(a) Leverage
              Ratio of the Credit Agreement shall cease and such section
              shall continue as provided in the Credit Agreement on January 2,
              2002.

          (b) The provision in paragraph 2(o) of the Third Amendment to Credit
     Agreement (as modified by paragraph 2(j) of the Fourth Amendment to Credit
     Agreement), which modifies Section 6.1(c) Interest Coverage Ratio of the
     Credit Agreement, is hereby modified as follows:

               (o) Section 6.1(c) Interest Coverage Ratio of the Credit
          Agreement shall be abated in its entirety as it presently exists
          through January 1, 2002 and shall be modified as follows:

               (c) Interest Coverage Ratio. Permit the Interest Coverage Ratio,
          as of the end of each fiscal quarter ending during the period
          specified below, to be less than the amount set forth opposite such
          period:

<TABLE>
<CAPTION>

            ---------------------------------------------------------------------------------------
                                                                     Interest Coverage Ratio Must
              Last Day of Fiscal Quarter During Period                       Not Be Less Than
            ---------------------------------------------------------------------------------------
              <S>                                                    <C>
            ---------------------------------------------------------------------------------------
              December 31, 2000 through March 30, 2001                        1.40 to 1
            ---------------------------------------------------------------------------------------
              March 31, 2001 through June 29, 2001                            1.10 to 1
            ---------------------------------------------------------------------------------------
              June 30, 2001 through September 29, 2001                        1.00 to 1
            ---------------------------------------------------------------------------------------
              September 30, 2001 through December 30, 2001                    1.25 to 1
            ---------------------------------------------------------------------------------------
              December 31, 2001                                               1.65 to 1
            ---------------------------------------------------------------------------------------
</TABLE>

              provided, however, that Interest Coverage Ratio for September 30,
              2001, shall be calculated on the basis of calendar year 2001 to
              date, rather than a rolling twelve month basis, and further
              provided, however, the abatement of Section 6.1(c) Interest
              Coverage Ratio of the Credit Agreement shall cease on January 2,
              2002, and such section shall continue as provided in the Credit
              Agreement immediately before the effective date of this
              Amendment, except that the words "equal or exceed" in the fifth
              line of Section 6.1(c) shall be changed to "be less than".

     3. Sale of Assets. The provisions of Section 2.10 (c) and Section 6.5 of
the Credit Agreement notwithstanding, Borrowers are permitted to sell the assets
described on Exhibit A-5

                                       2

<PAGE>

attached hereto and by this reference incorporated herein, subject to
fulfillment, to the satisfaction of Agent and its counsel, of the following
terms:

        (a) In addition to any other amounts due under the Credit Agreement,
Borrowers shall have paid to Agent, for the ratable benefit of the Banks, the
sum of Two Hundred Fifty Thousand Dollars ($250,000), on or prior to the date of
this Amendment. Such amount and all other amounts required to be paid hereunder
shall be applied as prepayment of the principal of Term Loan B. Such payments
shall be applied in the inverse order of maturity.

        (b) In addition to any other amounts due under the Credit Agreement,
Borrowers shall pay to Agent, for the ratable benefit of the Banks, the sum of
One Hundred Twenty-Five Thousand Dollars ($125,000), on or prior to March 15,
2002, which amount shall be applied as a prepayment of the principal of Term
Loan B as provided in subparagraph 3 (a) above.

        (c) In addition to any other amounts due under the Credit Agreement,
Borrowers shall pay to Agent, for the ratable benefit of the Banks, the sum of
Fifty Thousand Dollars ($50,000) each, on or prior to September 30, 2002 and
March 31, 2003, which amounts shall be applied as a prepayment of the principal
of Term Loan B as provided in subparagraph 3 (a) above.

        (d) This authorization of sale of assets shall not be deemed to be a
waiver of the provisions of Section 2.10 (c) or Section 6.5 of the Credit
Agreement or any other provision thereof which prohibits or restricts sale of
any other assets of Borrowers.

     4. Amendment to the Loan Documents. All references to the Credit Agreement
in the Loan Documents and in any documents executed in connection therewith
shall be deemed to refer to the Credit Agreement as amended by this Amendment.

     5. Ratification of the Loan Documents. Notwithstanding anything to the
contrary herein contained or any claims of the parties to the contrary, the
Agent, the Banks and the Borrowers agree that the Loan Documents and each of the
documents executed in connection therewith are in full force and effect and each
such document shall remain in full force and effect, as further amended by this
Amendment, and each of the Borrowers hereby ratifies and confirms its
obligations thereunder.

     6. Representations and Warranties.

        (a) Each Borrower hereby certifies that (i) the representations and
warranties of such Borrower in the Credit Agreement as amended herein are true
and correct in all material respects as of the date hereof, as if made on the
date hereof, provided that, for purposes of this Amendment, only: (x) the
representations and warranties made in Section 3.1(a) and (b) and 3.21 of the
Credit Agreement shall relate to the most recent financial statements of the
type referred to therein which have been given by the Borrowers to the Banks
(but the foregoing shall not be a waiver of any Default or Event of Default
based on any representation or warranty made by the Borrowers in the Credit
Agreement or any amendment thereof, prior to this Amendment, being untrue at the
time made, or for any breach of any covenant contained in the Credit Agreement,
as

                                       3

<PAGE>

amended prior to the date of this Amendment); (y) the representations and
warranties made in Section 3.1(c) of the Credit Agreement shall be made as of
the date of this Amendment and not as of the Closing Date; and (z) the
representations and warranties made in Section 3.2 of the Credit Agreement shall
refer to Material Adverse Effect since the last audited consolidated financial
statements of the Borrowers provided to the Banks by the Borrowers, instead of
since September 30, 1999 (but the foregoing shall not be a waiver of any Default
or Event of Default based on any representation or warranty made by the
Borrowers in the Credit Agreement or any amendment thereof, prior to this
Amendment, being untrue at the time made, or for any breach of any covenant
contained in the Credit Agreement, as amended prior to the date of this
Amendment); and (ii) no Event of Default and no event which could become an
Event of Default with the passage of time or the giving of notice, or both,
under the Credit Agreement or the other Loan Documents exists on the date
hereof.

        (b) Each Borrower further represents that it has all the requisite power
and authority to enter into and to perform its obligations under this Amendment,
and that the execution, delivery and performance of this Amendment have been
duly authorized by all requisite action and will not violate or constitute a
default under any provision of any applicable law, rule, regulation, order,
writ, judgment, injunction, decree, determination or award presently in effect
or of the Articles of Incorporation or by-laws of such Borrower, or of any
indenture, note, loan or credit agreement, license or any other agreement, lease
or instrument to which such Borrower is a party or by which such Borrower or any
of its properties are bound.

        (c) Each Borrower also further represents that its obligation to repay
the Loans, together with all interest accrued thereon, is absolute and
unconditional, and there exists no right of set off or recoupment, counterclaim
or defense of any nature whatsoever to payment of the Loans, and each Borrower
further represents that the Agents and Banks have fully performed all of their
respective obligations under the Loan Documents through the date of this
Amendment.

        (d) Each Borrower also further represents that there have been no
changes to the Articles of Incorporation, by-laws or other organizational
documents of each such Borrower since the most recent date true and correct
copies thereof were delivered to the Agent.

     7. Conditions Precedent. The effectiveness of the amendments set forth
herein is subject to the fulfillment, to the satisfaction of the Agent and its
counsel, of the following conditions precedent:

        (a) The Borrowers shall have delivered to the Agent the following, all
of which shall be in form and substance satisfactory to the Agent and shall be
duly completed and executed:

            (i) This Amendment and the consents of the Guarantor and the
     Subordinated Creditors as attached hereto; and

            (ii) The Amendment to Security Agreement which adds CECO Abatement
     Systems, Inc. as a Debtor; updates the representations and warranties

                                       4

<PAGE>

          set forth in the Security Agreement dated December 7, 1999 as to all
          Debtors; and authorizes Agent to file such financing and continuation
          statements as Agent deems necessary or appropriate in order to perfect
          and continue the perfection of the security interests created by the
          Security Agreement, without the signature of any Debtor, including,
          without limitation, "in lieu of" filings.

               (iii) Such additional documents, certificates and information as
          the Agent may require pursuant to the terms hereof or otherwise
          reasonably request.

          (b) After giving effect to the amendments contained herein, the
representations and warranties set forth in the Credit Agreement shall be true
and correct on and as of the date hereof.

           (c) After giving effect to the amendments contained herein, no Event
of Default hereunder, and no event which, with the passage of time or the giving
of notice, or both, would become such an Event of Default shall have occurred
and be continuing as of the date hereof.

          (d) The Borrowers shall have paid the reasonable fees and
disbursements of the Agent's counsel incurred in connection with this Amendment.

     8. No Waiver. Except as expressly provided herein, this Amendment does not
and shall not be deemed to constitute a waiver by the Agent or the Banks of any
Event of Default, or of any event which with the passage of time or the giving
of notice or both would constitute an Event of Default, nor does it obligate the
Agent or the Banks to agree to any further modifications to the Credit Agreement
or any other Loan Document or constitute a waiver of any of the Agent's or the
Banks' other rights or remedies.

     9. Waiver and Release. The Borrowers each on behalf of themselves, their
agents, employees, officers, directors, successors and assigns, do hereby waive
and release Agent and Banks, their agents, employees, officers, directors,
affiliates, parents, successors and assigns, from any claims arising from or
related to administration of the Credit Agreement and Loan Document and any
course of dealing among the parties not in compliance with those agreements from
the inception of the Credit Agreement whether known or unknown through the date
of execution and delivery of this Amendment.

     10. Effective Date. The parties hereto agree that the provisions of
paragraph 2 of this Amendment shall for all purposes be deemed to be effective
as of December 31, 2001and for all purposes the Credit Agreement shall be deemed
to have been amended as of such date to reflect the amendments to the Credit
Agreement set forth in such paragraph, even though this Amendment is executed
after such date.

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment as of
the day and year first above written.

                                       5

<PAGE>

                             CECO GROUP, INC.

                             By: /s/ Marshall J. Morris
                                ------------------------------------------------
                             Name:
                             Title:

                             CECO FILTERS, INC.

                             By: /s/ Marshall J. Morris
                                ------------------------------------------------
                             Name:
                             Title:

                             AIR PURATOR CORPORATION

                             By: /s/ Marshall J. Morris
                                ------------------------------------------------
                             Name:
                             Title:

                             NEW BUSCH CO., INC.

                             By: /s/ Marshall J. Morris
                                ------------------------------------------------
                             Name:
                             Title:

                             THE KIRK & BLUM MANUFACTURING COMPANY

                             By: /s/ Marshall J. Morris
                                ------------------------------------------------
                             Name:
                             Title:

                                       6

<PAGE>

                             KBD/TECHNIC, INC.

                             By: /s/ Marshall J. Morris
                                ------------------------------------------------
                             Name:
                             Title:

                             CECO ABATEMENT SYSTEMS, INC.

                             By: /s/ Marshall J. Morris
                                ------------------------------------------------
                             Name:
                             Title:

                             PNC BANK, NATIONAL ASSOCIATION, as
                             Agent and as a Bank

                             By: /s/ William C. Miles
                                ------------------------------------------------
                             Name:  /s/ William C. Miles
                             Title: /s/ Vice President

                             FIFTH THIRD BANK, as a Bank

                             By: /s/ David R. Alexander
                                ------------------------------------------------
                             Name:  /s/ David R. Alexander
                             Title: /s/ Assistant Vice President

                             BANK ONE, NA, as a Bank

                             By: /s/ Gary K. Myers
                                ------------------------------------------------
                             Name: /s/ Gary K. Myers
                             Title: /V.P./

                                       7

<PAGE>

                               GUARANTOR'S CONSENT

     By Corporate Guaranty, dated December 7, 2000 (the "Guaranty"), the
undersigned (the "Guarantor") guaranteed to the Agent and the Banks, subject to
the terms and conditions set forth therein, the prompt payment and performance
of all of the Obligations (as defined therein). The Guarantor consents to the
Borrowers' execution of the foregoing Fifth Amendment to Credit Agreement. The
Guarantor hereby acknowledges and agrees that the Guaranty remains unaltered and
in full force and effect and is hereby ratified and confirmed in all respects.

                                      CECO ENVIRONMENTAL CORP.

                                      By:
                                         ---------------------------------------
                                      Name:
                                      Title:

                                       8

<PAGE>

                         SUBORDINATED CREDITOR'S CONSENT

     The undersigned (the "Subordinated Creditor") is a party to the
Subordination Agreement with the Agent and the Banks and other subordinated
creditors, dated December 7, 2000 (the "Subordination Agreement"). The
Subordinated Creditor consents to the Borrowers' execution of the foregoing
Fifth Amendment to Credit Agreement. The Subordinated Creditor hereby
acknowledges and agrees that the Subordination Agreement remains unaltered and
in full force and effect and is hereby ratified and confirmed in all respects.

                                         GREEN DIAMOND OIL CORP.

                                         By:
                                            ------------------------------------
                                         Name:
                                         Title

                                       9

<PAGE>

                         SUBORDINATED CREDITOR'S CONSENT

     The undersigned (the "Subordinated Creditor") is a party to the
Subordination Agreement with the Agent and the Banks and other subordinated
creditors, dated December 7, 2000 (the "Subordination Agreement"). The
Subordinated Creditor consents to the Borrowers' execution of the foregoing
Fifth Amendment to Credit Agreement. The Subordinated Creditor hereby
acknowledges and agrees that the Subordination Agreement remains unaltered and
in full force and effect and is hereby ratified and confirmed in all respects.

                                       ICS TRUSTEE SERVICES, LTD.

                                       By:
                                          --------------------------------------
                                       Name:
                                       Title

                                       10

<PAGE>

                         SUBORDINATED CREDITOR'S CONSENT

     The undersigned (the "Subordinated Creditor") is a party to the
Subordination Agreement with the Agent and the Banks and other subordinated
creditors, dated December 7, 2000 (the "Subordination Agreement"). The
Subordinated Creditor consents to the Borrowers' execution of the foregoing
Fifth Amendment to Credit Agreement. The Subordinated Creditor hereby
acknowledges and agrees that the Subordination Agreement remains unaltered and
in full force and effect and is hereby ratified and confirmed in all respects.

                                       HARVEY SANDLER

                                       -----------------------------------------

                                       11<PAGE>

                                                                   Exhibit 10.44

                Option for the Purchase of Shares of Common Stock
                -------------------------------------------------

                                                                   25,000 Shares

FOR VALUE RECEIVED, CECO Environmental Corp. (the "Company"), hereby certifies
that Jason DeZwirek, or a permitted assign thereof, is entitled to purchase from
the Company, at any time or from time to time commencing April 5, 2002, and
prior to 5:00 P.M., P.S.T., on October 5, 2011, Twenty-five Thousand (25,000)
fully paid and nonassessable shares of the common stock, of the Company for a
purchase price of $2.01 per share. (Hereinafter, (i) said common stock, together
with any other equity securities which may be issued by the Company with respect
thereto or in substitution therefor, is referred to as the "Common Stock," (ii)
the shares of the Common Stock purchasable hereunder or under any other Option
or (as hereinafter defined) are referred to as the "Option Shares," (iii) the
price payable hereunder for each of the Option Shares is referred to as the
"Option Exercise Price," (iv) this Option, and all options hereafter issued in
exchange or substitution for this Option or such other options are referred to
as the "Options" and (v) the holder of this Option is referred to as the
"Holder" and the holder of this Option and all other Options are referred to as
the "Holders"). The Option Exercise Price is subject to adjustment as
hereinafter provided:

1.   Exercise of Option.
     ------------------

     a)   Exercise for Cash
          -----------------

     This Option may be exercised, in whole at any time or in part from time to
     time, commencing April 5, 2002, and prior to 5:00 P.M., P.S.T., on October
     5, 2011, by the Holder by the surrender of this Option (with the
     subscription form at the end hereof duly executed) at the address set forth
     in Subsection 8(a) hereof, together with proper payment of the Per Share
     Option Price times the number of shares of Common Stock to be received.
     Payment for Option Shares shall be made by certified or official bank check
     payable to the order of the Company or if applicable, without cash pursuant
     to a cashless net exercise. If this Option is exercised in part, this
     Option must be exercised for a number of whole shares of the Common Stock,
     and the Holder is entitled to receive a new Option Covering the Option
     Shares which have not been exercised. Upon such surrender of this Option
     the Company will (a) issue a certificate or certificates in the name of the
     Holder for the largest number of whole shares of the Common Stock to which
     the Holder shall be entitled and, if this Option is exercised in whole, in
     lieu of any fractional share of the Common Stock to which the Holder shall
     be entitled, pay to the Holder cash in an amount equal to the fair value of
     such fractional share (determined in such reasonable manner as the Board of
     Directors of the Company shall determine), and (b) deliver the other
     securities and properties receivable upon the exercise of this Option, or
     the proportionate part thereof if this Option is exercised in part,
     pursuant to the provisions of this Option.

                                       1

<PAGE>

     b)   Cashless Exercise
          -----------------

     In lieu of exercising this Option in the manner set forth in paragraph l(a)
     above, this Option may be exercised, in whole or in part, by surrender of
     the Option without payment of any other consideration, commission or
     remuneration, by execution of the cashless exercise subscription form (at
     the end hereof, duly executed). The number of shares to be issued in
     exchange for the Option will be computed by subtracting the Option Exercise
     Price from either (i) the closing bid price of the Common Stock on the date
     of receipt of the cashless exercise subscription form, or (ii) the most
     recent negotiated value used in connection with any sale of the Company's
     securities or in connection with any business combination involving the
     Company, and multiplying that amount by the number of shares represented by
     the Option, and dividing by the closing bid price as of the same date.

2.   Reservation of Option Shares, Listing.
     -------------------------------------

     The Company agrees that, prior to the expiration of this Option, the
     Company will at all times have authorized and in reserve, and will keep
     available, solely for issuance or delivery upon the exercise of this
     Option, the shares of the Common Stock and other securities and properties
     as from time to time shall be receivable upon the exercise of this Option,
     free and clear of all restrictions on sale or transfer (except for
     applicable state or federal securities law restrictions) and free and clear
     of all pre-emptive rights.

3.   Protection Against Dilution.
     ---------------------------

     a)   If, at any time or from time to time after the date of this Option,
          the Company shall issue or distribute (for no consideration) to the
          holders of shares of Common Stock evidences of its indebtedness, any
          other securities of the Company or any cash, property or other assets
          (excluding a subdivision, combination or reclassification, or dividend
          or distribution payable in shares of Common Stock, referred to in
          Subsection 3(b), and also excluding cash dividends or cash
          distributions paid out of net profits legally available therefor if
          the full amount thereof, together with the value of other dividends
          and distributions made substantially concurrently therewith or
          pursuant to a plan which includes payment thereof, is equivalent to
          not more than 5% of the Company's net worth) (any such nonexcluded
          event being herein called a "Special Dividend"), the Option Exercise
          Price shall be adjusted by multiplying the Option Exercise Price then
          in effect by a fraction, the numerator of which shall be the then
          current market price of the Common Stock (defined as the average for
          the thirty consecutive business days immediately prior to the record
          date of the daily closing price of the Common Stock as reported by the
          principal exchange or market on which the Common Stock is listed) less
          the fair market value (as determined by the Company's Board of
          Directors) of the evidences of indebtedness, securities or property,
          or other assets issued or distributed in such Special Dividend
          applicable to one share of Common Stock and the denominator of which
          shall be such then current market price per share of Common Stock. An
          adjustment made pursuant to

                                       2

<PAGE>

          this Subsection 3(a) shall become effective immediately after the
          record date of any such Special Dividend.

     b)   In case the Company shall hereafter (i) pay a dividend or make a
          distribution on its capital stock in shares of Common Stock, (ii)
          subdivide its outstanding shares of Common Stock into a greater number
          of shares, (iii) combine its outstanding shares of Common Stock into a
          smaller number of shares or (iv) issue by reclassification of its
          Common Stock any shares of capital stock of the Company, the Option
          Exercise Price shall be adjusted so that the Holder of any Option upon
          the exercise hereof shall be entitled to receive the number of shares
          of Common Stock or other capital stock of the Company which he would
          have owned immediately prior thereto. An adjustment made pursuant to
          this Subsection 3(b) shall become effective immediately after the
          record date in the case of a dividend or distribution and shall become
          effective immediately after the effective date in the case of a
          subdivision, combination or reclassification. If, as a result of an
          adjustment made pursuant to this Subsection 3(b), the Holder of any
          Option thereafter surrendered for exercise shall become entitled to
          receive shares of two or more classes of capital stock or shares of
          Common Stock and other capital stock of the Company, the Board of
          Directors (whose determination shall be conclusive and shall be
          described in a written notice to the Holder of any Option promptly
          after such adjustment) shall reasonably determine the allocation of
          the adjusted Option Exercise Price between or among shares of such
          classes or capital stock or shares of Common Stock and other capital
          stock.

     c)   In case of any capital reorganization or reclassification, or any
          consolidation or merger to which the Company is a party other than a
          merger or consolidation in which the Company is the continuing
          corporation, or in case of any sale or conveyance to another entity of
          the property of the Company as an entirety or substantially as an
          entirety, or in the case of any statutory exchange of securities with
          another corporation (including any exchange effected in connection
          with a merger of a third corporation into the Company), the Holder of
          this Option shall have the right thereafter to convert such Option
          into the kind and amount of securities, cash or other property which
          he would have owned or have been entitled to receive immediately after
          such reorganization, reclassification, consolidation, merger,
          statutory exchange, sale or conveyance had this Option been converted
          immediately prior to the effective date of such reorganization,
          reclassification, consolidation, merger, statutory exchange, sale or
          conveyance and in any such case, if necessary, appropriate adjustment
          shall be made in the application of the provisions set forth in this
          Section 3 with respect to the rights and interests thereafter of the
          Holder of this Option to the end that the provisions set forth in this
          Section 3 shall thereafter correspondingly be made applicable, as
          nearly as may reasonably be, in relation to any shares of stock or
          other securities or be, in relation to any shares of stock or other
          securities or property thereafter deliverable on the conversion of
          this Option. The above provisions of this Subsection 3(c) shall
          similarly apply to successive reorganizations, reclassifications,
          consolidations, mergers, statutory exchanges, sales or

                                       3

<PAGE>

          conveyances. The issuer of any shares of stock or other securities or
          property thereafter deliverable on the conversion of this Option shall
          be responsible for all of the agreements and obligations of the
          Company hereunder. Notice of any such reorganization,
          reclassification, consolidation, merger, statutory exchange, sale or
          conveyance and of said provisions so proposed to be made, shall be
          mailed to the Holders of the Options not less than 10 days prior to
          such event. A sale of all or substantially all of the assets of the
          Company for a consideration consisting primarily of securities shall
          be deemed a consolidation or merger for the foregoing purposes.

     d)   No adjustment in the Option Exercise Price shall be required unless
          such adjustment would require an increase or decrease of at least
          $0.05 per share of Common Stock; provided, however, that any
          adjustments which by reason of this Subsection 3(d) are not required
          to be made shall be carried forward and taken into account in any
          subsequent adjustment; provided further, however, that adjustments
          shall be required and made in accordance with the provisions of this
          Section 3 (other than this Subsection 3(d)) not later than such time
          as may be required in order to preserve the tax-free nature of a
          distribution to the Holder of this Option or Common Stock issuable
          upon exercise hereof. All calculations under this Section 3 shall be
          made to the nearest cent. Anything in this Section 3 to the contrary
          notwithstanding, the Company shall be entitled to make such reductions
          in the Option Exercise Price, in addition to those required by this
          Section 3, as it in its discretion shall deem to be advisable in order
          that any stock dividend, subdivision of shares or distribution of
          rights to purchase stock or securities convertible or exchangeable for
          stock hereafter made by the Company to its shareholders shall not be
          taxable.

     e)   Whenever the Option Exercise Price is adjusted as provided in this
          Section 3 and upon any modification of the rights of a Holder of
          Options in accordance with this Section 3, the Company shall promptly
          obtain, at its expense, a certificate of a firm of independent public
          accountants of recognized standing selected by the Board of Directors
          (who may be the regular auditors of the Company) setting forth the
          Option Exercise Price and the number of Option Shares after such
          adjustment or the effect of such modification, a brief statement of
          the facts requiring such adjustment or modification and the manner of
          computing the same and cause copies of such certificate to be mailed
          to the Holders of the Options.

     f)   If the Board of Directors of the Company shall declare any dividend or
          other distribution with respect to the Common Stock, other than a cash
          distribution out of earned surplus, the Company shall mail notice
          thereof to the Holders of the Options not less than 10 days prior to
          the record date fixed for determining shareholders entitled to
          participate in such dividend or other distribution.

4.   Fully Paid Stock, Taxes.
     -----------------------

     The Company agrees that the shares of the Common Stock represented by each
     and every certificate for Option Shares delivered on the exercise of this
     Option shall, at the time of

                                       4

<PAGE>

     such delivery, be validly issued and outstanding, fully paid and
     nonassessable, and not subject to pre-emptive rights, and the Company will
     take all such actions as may be necessary to assure that the par value or
     stated value, if any, per share of the Common Stock is at all times equal
     to or less than the then Option Exercise Price. The Company further
     covenants and agrees that it will pay, when due and payable, any and all
     Federal and state stamp, original issue or similar taxes which may be
     payable in respect of the issue of any Option Share or certificate
     therefor.

5.   Transferability.
     ---------------

     Subject to compliance with federal and applicable state securities laws and
     the provisions of Section 13, the Holder of any Option may, prior to
     exercise or expiration thereof, surrender such Option at the principal
     office of the Company for transfer or exchange. Within a reasonable time
     after notice to the Company from a registered Holder of its intention to
     make such exchange and without expense (other than transfer taxes, if any)
     to such registered Holder, the Company shall issue in exchange therefor
     another Option or Options, in such denominations as requested by the
     registered Holder, for the same aggregate number of Option Shares so
     surrendered and containing the same provisions and subject to the same
     terms and conditions as the Option(s) so surrendered. The Company may treat
     the registered Holder of this Option as he or it appears on the Company's
     books at any time as the Holder for all purposes. The Company shall permit
     any Holder of a Option or his duly authorized attorney, upon written
     request during ordinary business hours, to inspect and copy or make
     extracts from its books showing the registered holders of Options. All
     options issued upon the transfer or assignment of this Option will be dated
     the same date as this Option, and all rights of the Holder thereof shall be
     identical to those of the Holder.

6.   Loss, etc., of Option.
     ---------------------

     Upon receipt of evidence satisfactory to the Company of the loss, theft,
     destruction or mutilation of this Option, and of indemnity reasonably
     satisfactory to the Company, if lost, stolen or destroyed, and upon
     surrender and cancellation of this Option, if mutilated, the Company shall
     execute and deliver to the Holder a new Option of like date, tenor and
     denomination.

7.   Option Holder Not Shareholders.
     ------------------------------

     Except as otherwise provided herein, this Option does not confer upon the
     Holder any right to vote or to consent to or receive notice as a
     shareholder of the Company, as such, in respect of any matters whatsoever,
     or any other rights or liabilities as a shareholder, prior to the exercise
     hereof.

8.   Communication.
     -------------

     No notice or other communication under this Option shall be effective
     unless, but any notice or other communication shall be effective and shall
     be deemed to have been given if, the same is in writing and (i) is
     personally delivered, (ii) five days after such written material is

                                       5

<PAGE>

     mailed by first-class mail, postage prepaid, or (iii) one day after such
     written material is sent by a nationally recognized overnight courier,
     addressed to:

     a)   the Company at 505 University Avenue, Suite 1400, Toronto, Ontario M5G
          1X3, Canada, Attn: Phillip DeZwirek or such other address as the
          Company has designated in writing to the Holder; or

     b)   the Holder at 505 University Avenue, Suite 1400, Toronto, Ontario M5G
          1X3, Canada, or such other address as the Holder has designated in
          writing to the Company.

9.   Headings.
     --------

     The headings of this Option have been inserted as a matter of convenience
     and shall not affect the construction hereof.

10.  Withholding.
     -----------

     The Holder acknowledges that, upon any exercise of this Option, the Company
     shall have the right to require the Holder to pay to the Company an amount
     equal to the amount the Company is required to withhold as a result of such
     exercise for federal and state income tax purposes.

11.  Applicable Law.
     --------------

     This Option shall be governed by and construed in accordance with the law
     of the State of New York without giving effect to the principles of
     conflicts of law thereof.

12.  Securities Law Compliance.
     -------------------------

     The exercise of all or any parts of this Option shall only be effective at
     such time as counsel to the Company shall have determined that the issuance
     and delivery of Common Stock pursuant to such exercise will not violate any
     state or federal securities or other laws. Holder may be required by the
     Company, as a condition of the effectiveness of any exercise of this
     Option, to agree in writing that all Common Stock to be acquired pursuant
     to such exercise shall be held, until such time that such Common Stock is
     registered or exempt from registration and freely tradable under applicable
     state and federal securities laws, for Holder's own account without a view
     to any further distribution thereof, that the certificates for such shares
     shall bear an appropriate legend to that effect and that such shares will
     be not transferred or disposed of except in compliance with applicable
     state and federal securities laws.

13.  Nontransferability.
     ------------------

     Except as otherwise agreed to by the Company, during the lifetime of
     Holder, this Option shall be exercisable only by Holder or by the Holder's
     guardian or other legal representative,

                                       6

<PAGE>

     and shall not be assignable or transferable by Holder, in whole or in part,
     other than by will or by the laws of descent and distribution.

14.  Scope of Agreement.
     ------------------

     This Agreement shall bind and inure to the benefit of the Company and its
     successors and assigns and Holder and any successor or successors of Holder
     permitted by Section 13 above.

IN WITNESS WHEREOF, CECO Environmental Corp. has caused this Option to be signed
by its Chairman, as of this 5th day of October, 2001.

                                      CECO ENVIRONMENTAL CORP.

                                      By:     /s/ Phillip DeZwirek
                                            ----------------------
                                      Name: Phillip DeZwirek
                                      Title:Chairman and Chief Executive Officer

                                       7

<PAGE>

                                SUBSCRIPTION
                                ------------

The undersigned,                      , pursuant to the provisions of the
                ----------------------
foregoing Option, hereby agrees to subscribe for and purchase shares of the
Common Stock of CECO Environmental Corp. covered by said Option, and makes
payment therefor in a manner specified in the Option in full at the price per
share provided by said Option.

Dated:                                      Signature:

                                            Address:

                                       8

<PAGE>

                                 ASSIGNMENT
                                 ----------

FOR VALUE RECEIVED                    hereby sells, assigns and transfers unto
                  -------------------
            the foregoing Option and all rights evidenced thereby, and does
------------
irrevocably constitute and appoint                        , attorney, to
                                   -----------------------
transfer said Option on the books of                      .
                                     ---------------------

Dated:                                      Signature:

                                            Address:

                                       9

<PAGE>

                               PARTIAL ASSIGNMENT
                               ------------------

FOR VALUE RECEIVED                     hereby assigns and transfers unto
                  --------------------
                    the right to purchase                shares of the
-------------------                       --------------
Common Stock of CECO Environmental Corp. by the foregoing Option, and a
proportionate part of said Option and the rights evidenced hereby, and does
irrevocably constitute and appoint attorney, to transfer that part of said
Option on the books of                      .
                      ----------------------

Dated:                                      Signature:

                                            Address:

                         CASHLESS EXERCISE SUBSCRIPTION
                         ------------------------------

The undersigned                         pursuant to the provisions of the
               ------------------------
foregoing Option, hereby agrees to subscribe to that number of shares of
Common Stock of CECO Environmental Corp. as are issuable in accordance with
the formula set forth in paragraph l(b) of the Option, and makes payment
therefore in full by surrender and delivery of this Option.

Dated:                                      Signature:

                                            Address:

                                       10

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