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J.S. Held Acquires Clark Seif Clark, Strengthening West Coast Capabilities for Environmental Claims, Disputes, and Catastrophe Response
Read MoreDerrick Denis joined J.S. Held in May of 2026 as part of J.S. Held's acquisition of Clark Seif Clark, Inc.
Derrick is a recognized industry leader, inventor, educator, and author. Since the early 1990’s, he has provided professional industrial hygiene (IH), environmental health and safety (EHS), infection control (IC), and indoor environmental quality (IEQ) services domestically and abroad. As a sought-after presenter, he has delivered hundreds of educational sessions for associations and private groups around the world.
Derrick leverages a B.S. in Environmental Science, multiple certifications and licenses, and extensive experience to serve as a respected, impartial expert witness. He has supported more than 100 state and federal cases on behalf of both plaintiffs and defendants, from depositions through trial testimony. Actively engaged in the industry, Derrick has held board positions with organizations including the Indoor Air Quality Association (IAQA), Environmental Information Association–Arizona Chapter (EIA‑AZ), and the American Council for Accredited Certifications (ACAC). He is also an inventor and patent holder, including a disposable N95 fit test hood for healthcare use and Sewer Gas Solutions®, a patented product designed to prevent sewer gas and pest infiltration through plumbing traps.
Prior to joining J.S. Held, Derrick was the Senior Vice President at Clark Seif Clark, Inc. (CSC). Since 2000, he developed new services, conducted team training, managed marketing and sales efforts, and managed the Chandler office. As a practitioner, he also provides investigative and subject matter expert services to clientele.
J.S. Held is recognized as an ENR Top 200 Environmental Consulting Firm and industry leader in the Verdantix Green Quadrant for Sustainability & ESG Consulting.
