| # | Company name | Role | # of projects |
|---|---|---|---|
| 581 | No-Burn Canada | Fire protection engineering | 0 |
| 582 | Norcal Fire Protection | Fire protection engineering | 0 |
| 583 | Norco Fire Protection | Fire protection engineering | 0 |
| 584 | Nortec Fire Protection | Fire protection engineering | 1 |
| 585 | North County Fire Protection | Fire protection engineering | 1 |
| 586 | North East Fire Protection | Fire protection engineering | 2 |
| 587 | Northeastern Insulation Inc. | Fire protection engineering | 0 |
| 588 | Northstar Fire Protection | Fire protection engineering | 31 |
| 589 | Notifier | Fire protection engineering | 2 |
| 590 | Notifier Polska Sp z o.o. | Fire protection engineering | 4 |
| 591 | Nova Fire Protection Company, LLC | Fire protection engineering | 0 |
| 592 | Nova Fire Protection, Inc. | Fire protection engineering | 5 |
| 593 | Novar AS | Fire protection engineering | 1 |
| 594 | NVM Fireproofing | Fire protection engineering | 1 |
| 595 | Ökotec Beratende Ingenieure und Gutachter | Fire protection engineering | 6 |
| 596 | Olympic Fire Protection Company | Fire protection engineering | 0 |
| 597 | Olympic Fire Protection Corp | Fire protection engineering | 0 |
| 598 | Omlid & Swinney Fire Sprinkler Systems | Fire protection engineering | 1 |
| 599 | Omni Fireproofing Company, LLC | Fire protection engineering | 1 |
| 600 | Omni Fireproofing Company. Inc. | Fire protection engineering | 2 |