Clapper, Patti, Schweizer & Mason California Law Firm Representing Clients with Success & Care for Over 30 Years Clapper, Patti, Schweizer & Mason (CPSM) is a plaintiffs law firm, representing clients who have been injured by defective products, negligence or asbestos. Jack Clapper was a pioneer in asbestos litigation in California, with unmatched experience in mesothelioma lawsuits and asbestos bankruptcy funds. For over 3 decades, the lawyers at CPSM successfully litigated mesothelioma and personal injury cases throughout the United States, and have obtained hundreds of millions of dollars in recoveries for our clients. All cases are accepted on a contingency basis.