Special Hazard Systems are utilized in instances where a standard sprinkler system would be inappropriate for fire suppression. Examples of these instances may include: computer rooms, data storage faciliites, medical records, museum exhibits, hostorical sites, flammable chemicals, etc.
Below is the link to a number of NFPA Standards that address Special Hazard Systems:
NFPA 12 CO2 Systems
NFPA 12A Halon 1301 Systems
NFPA 17 Dry Chemical Systems
NFPA 2001 Clean Agent Systems
NFPA 72 National Fire Alarm Code