FIRST AMENDMENT TO CREDIT AGREEMENT

Exhibit 4.1

FIRST AMENDMENT TO CREDIT AGREEMENT

     This FIRST AMENDMENT TO CREDIT AGREEMENT (this “Amendment”) is entered into as of July 3, 2007 among AIRGAS, INC., a Delaware corporation (“Airgas” and also a “Borrower”), AIRGAS CANADA INC., a Canada corporation, and RED-D-ARC LIMITED, an Ontario corporation (each a “Canadian Borrower” and together with Airgas, the “Borrowers”), the Guarantors signatory hereto, the Lenders signatory hereto BANK OF AMERICA, N.A., as administrative agent for the Lenders (in such capacity, the “U.S. Agent”) and THE BANK OF NOVA SCOTIA, as Canadian administrative agent for the Lenders (in such capacity, the “Canadian Agent”). Capitalized terms used herein and not otherwise defined shall have the meanings set forth in the Credit Agreement (as defined below).

RECITALS

     WHEREAS, the Borrowers, the Guarantors, the Lenders and the Agents are parties to that certain Credit Agreement dated as of July 25, 2006 (the “Credit Agreement”).

     WHEREAS, Airgas intends to convert certain shares of Capital Stock of National Welders Supply Company, Inc., a North Carolina corporation (“National Welders”), into shares of Capital Stock of Airgas at which point National Welders shall become a Subsidiary of Airgas (the “Transaction”).

     WHEREAS, National Welders is a borrower under that certain $100 million credit agreement among National Welders, Bank of America, N.A., Wachovia Bank, National Association and Branch Banking and Trust Company (the “NWS Credit Agreement”).

     WHEREAS, the Required Lenders have agreed to amend certain terms of the Credit Agreement on the terms, and subject to the conditions, set forth below.

     NOW THEREFORE, for good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto agree as follows:

AGREEMENT

     1. Amendments to Credit Agreement. The following amendments shall become effective immediately upon the consummation of the Transaction:

     (a) Section 2.1 (U.S. Revolving Loans).

     (i) Section 2.1 of the Credit Agreement is amended by replacing “NINE HUNDRED SIXTY-SIX MILLION U.S. DOLLARS ($966,000,000)” with the following:

     “ONE BILLION SIXTY-SIX MILLION U.S. DOLLARS ($1,066,000,000)”

(b) Schedule 2.1(a) (Lenders and Commitments). Schedule 2.1(a) is amended and restated in its entirety as attached hereto.

     2. Additional Agreements of the Credit Parties. The Credit Parties covenant to the Agents and the Lenders that the NWS Credit Agreement will be terminated and repaid contemporaneously with the consummation of the Transaction. Failure to comply with this covenant shall be deemed an Event of Default under the Credit Agreement. Furthermore, the Credit Parties shall (a) cause National Welders to

become a U.S. Subsidiary Guarantor pursuant to Section 7.12 of the Credit Agreement and (b) pledge the Capital Stock of National Welders to the Collateral Agent pursuant to Section 7.13 of the Credit Agreement.

     3. Letters of Credit. The parties hereto agree that the letters of credit identified on Annex 1 attached hereto shall be deemed to be U.S. Letters of Credit, and from and after the date of this Amendment shall be subject to and governed by the terms and conditions of the Credit Agreement.

     4. Effectiveness; Conditions Precedent. This Amendment shall become effective upon receipt by the Agents of the following:

     (a) copies of this Amendment duly executed by the Credit Parties and the Required Lenders; and

     (b) copies of certified resolutions for Airgas approving the increase in the U.S. Revolving Committed Amount.

     5. Construction. This Amendment is a Credit Document executed pursuant to the Credit Agreement and shall (unless otherwise expressly indicated therein) be construed, administered and applied in accordance with the terms and provisions of the Credit Agreement.

     6. Representations and Warranties. Each Credit Party hereby represents and warrants that (i) each Credit Party that is party to this Amendment: (a) has the requisite corporate power and authority to execute, deliver and perform this Amendment, as applicable and (b) is duly authorized to, and has been authorized by all necessary corporate action, to execute, deliver and perform this Amendment, (ii) the representations and warranties contained in Article VI of the Credit Agreement are true and correct in all material respects on and as of the date hereof upon giving effect to this Amendment as though made on and as of such date (except for those which expressly relate to an earlier date) and (iii) no Default or Event of Default exists under the Credit Agreement on and as of the date hereof upon giving effect to this Amendment.

     7. Acknowledgment. The Guarantors acknowledge and consent to all of the terms and conditions of this Amendment and agree that this Amendment does not operate to reduce or discharge the Guarantors’ obligations under the Credit Agreement or the other Credit Documents. The Guarantors further acknowledge and agree that the Guarantors have no claims, counterclaims, offsets, or defenses to the Credit Documents and the performance of the Guarantors’ obligations thereunder or if the Guarantors did have any such claims, counterclaims, offsets or defenses to the Credit Documents or any transaction related to the Credit Documents, the same are hereby waived, relinquished and released in consideration of the Lenders’ execution and delivery of this Amendment.

     8. Counterparts. This Amendment may be executed by the parties hereto in several counterparts, each of which shall be deemed to be an original and all of which shall constitute together but one and the same agreement.

     9. Binding Effect. This Amendment, the Credit Agreement and the other Credit Documents embody the entire agreement between the parties and supersede all prior agreements and understandings, if any, relating to the subject matter hereof. These Credit Documents represent the final agreement between the parties and may not be contradicted by evidence of prior, contemporaneous or subsequent oral agreements of the parties. Except as expressly modified and amended in this Amendment, all the terms, provisions and conditions of the Credit Documents shall remain unchanged and shall continue in full force and effect.

     10. GOVERNING LAW. THIS AGREEMENT AND THE RIGHTS AND OBLIGATIONS OF THE PARTIES HEREUNDER SHALL BE GOVERNED BY AND CONSTRUED AND INTERPRETED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

     11. Severability. If any provision of this Amendment is determined to be illegal, invalid or unenforceable, such provision shall be fully severable and the remaining provisions shall remain in full force and effect and shall be construed without giving effect to the illegal, invalid or unenforceable provisions.

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     IN WITNESS WHEREOF, each of the parties hereto has caused a counterpart of this Amendment to be duly executed and delivered and this Amendment shall be effective as of the date first above written.