The Riverside Co. has closed a deal for RS Occupational Health, which the private equity firm plans to add on to portfolio company Disa Global Solutions.

RS, headquartered in Aberdeen, Scotland, provides occupational health services through three U.K. clinics. Terms of the deal were not disclosed.

Houston-based Disa provides workplace safety and compliance services for several industries, including the energy sector. This is Riverside's third add-on to the company, and the private equity firm expects it to increase Disa's international footprint and capabilities.

Fifth Street provided financing for the transactions, while Jones Day UK and KPMG UK provided Disa with legal counsel and accounting support, respectively.

Riverside, headquartered in Cleveland and New York, focuses on buying business valued at up to $200 million. In March, the firm sold swimwear company Arena to Swiss private equity firm Capvis. Also in March, the firm sold OnCourse Learning Co. to CIP Capital

Riverside's co-CEOs, Stewart Kohl and Béla Szigethy won Mergers & Acquisitions M&A Mid-Market Award for Dealmakers of the Year for 2013.