| # | Company name | Role | # of projects |
|---|---|---|---|
| 1 | Ökotec Beratende Ingenieure und Gutachter | Fire protection engineering | 6 |
| 2 | Olympic Fire Protection Company | Fire protection engineering | 0 |
| 3 | Olympic Fire Protection Corp | Fire protection engineering | 0 |
| 4 | Omlid & Swinney Fire Sprinkler Systems | Fire protection engineering | 1 |
| 5 | Omni Fireproofing Company, LLC | Fire protection engineering | 1 |
| 6 | Omni Fireproofing Company. Inc. | Fire protection engineering | 2 |
| 7 | Optimal Fire Protection | Fire protection engineering | 1 |
| 8 | Oslo Brannsikring | Fire protection engineering | 3 |
| 9 | Ottawa Sprinkler Installations Ltd. | Fire protection engineering | 4 |
| 10 | Overhead Fire | Fire protection engineering | 1 |
| 11 | Ozik Systems Ltd. | Fire protection engineering | 3 |
| 12 | Øresund Safety Advisers AB | Fire protection engineering | 4 |