[SAFETY-KLEEN LOGO]
                                                              
                                                           January 6, 1998     
 
Dear Safety-Kleen Shareholder:
 
  We, the Board of Directors, realize the enormous responsibility of
evaluating the offers for your Company. We believe that the $27 all-cash
merger agreement we have approved (the "Philip Merger") offers Safety-Kleen
shareholders value superior to the Laidlaw Environmental proposal. The Philip
Merger Agreement was entered into after your Board carefully evaluated the
risks and benefits of the alternatives available and unanimously agreed the
Philip Merger Agreement is in the best interests of the shareholders and other
constituencies which your Board considered.
 
  Laidlaw Environmental Services claims that the offer it made on November 20
is worth $30 per share, consisting of $15 in Laidlaw Environmental stock and
$15 cash, subject to certain adjustments. We firmly believe that it is not
worth $30 per share.
   
  As more fully discussed in clauses (v), (vii) and (viii) of "Item 4. The
Solicitation Or Recommendation--(b)(2) Reasons For The Recommendation" and 
"--(b)(1) Background" in the attached Schedule 14D-9:     
  . The stock portion of their offer is uncertain and could be worth
    significantly less than its claimed $15 value. Consider the following:
    --Laidlaw says it expects to achieve an estimated $100-130 million of
     "synergies". However, there is little overlap between Safety-Kleen's
     core service business and Laidlaw's landfill and incineration
     business. As a result, we do not believe that Laidlaw can accomplish
     even $50 million of synergies without significant reductions in
     service quality, revenue and profit.
       
    --The value of the stock portion of Laidlaw Environmental's offer is
     dependent upon its stock trading above $4.29 per share. As recently as
     December 17th and 18th, the stock closed below the minimum level.     
    --We believe that Laidlaw Environmental has materially underestimated
     the charges for depreciation and amortization that would result from
     its transaction. Accordingly, Laidlaw's future earnings would be
     significantly reduced.
    --Up to approximately 200 million Laidlaw Environmental shares would be
     issued in the transaction, which could quadruple the stock available
     in the public markets. It is questionable whether the market could
     absorb this substantial stock issuance without adversely affecting
     Laidlaw's stock price.
     
  . Laidlaw Environmental provides no guaranty as to how much will be paid in
    cash to Safety-Kleen shareholders. The nominal $15 in cash portion is
    subject to reduction, which Laidlaw has estimated could amount to $1.17
    per share.     
  . Considering the conditions in Laidlaw's offer, it is unlikely that its
    proposed transaction would close before mid-1998 at the earliest.
   
  Your Board also carefully considered the significant differences between the
business operations of Safety-Kleen and Laidlaw Environmental. Safety-Kleen
recycles; Laidlaw incinerates and puts wastes in the ground. The latter
results in much greater potential environmental liability. As a result of the
transaction, Laidlaw Inc., the parent company, would no longer own more than
50% of Laidlaw Environmental and therefore would remove from its balance sheet
the potential liabilities and environmental risks of Laidlaw Environmental,
which are discussed in clause (ix) of "Item 4. The Solicitation or
Recommendation--(b)(2) Reasons For The Recommendation" in the attached
Schedule 14D-9. Safety-Kleen shareholders, who could become owners of more
than 50% of Laidlaw Environmental if the transaction were completed, would
become subject to those risks.     
   
  We have called a special meeting of shareholders to approve the Philip
Merger which will be held on February 11, 1998. Detailed information
concerning this merger is set forth in the Proxy Statement enclosed herewith.
    
  The Board of Directors and management team at Safety-Kleen has, and will
continue to act with your best interests in mind. We appreciate your support
and confidence and will keep you fully informed of the process.
 
                                          Sincerely,
 
                                          /s/ Donald W. Brinckman
                                          Donald W. Brinckman
                                          Founder, Chairman and Chief
                                           Executive Officer
                                          For the Board of Directors