Alternative fire suppression systems are common in many commercial buildings throughout the United States. Wet-chemical, dry chemical, systems utilizing foam, clean agent, and carbon dioxide suppression systems fall under the general classification of alternative suppression systems. Many of these systems are designed to protect a specific hazard and may be used to supplement an overall sprinkler system or provide protection in a sensitive area. The first step in ensuring proper protection is the agent's compatibility with the protected hazard. Alternative fire protection systems will protect a specific hazard when water is not a key suppression agent. This article will review some of the basic concepts of three of these types of alternative fire suppression systems; wet chemical, dry chemical, and foam suppression systems.
Wet Chemical Systems
Wet Chemical fire suppression systems are typically pre-engineered based on typical hazards that are presented in kitchen cooking line ups. Wet chemical suppression systems are required in kitchen cooking areas where a type I hood is required by a mechanical code. The design and installation of wet chemical systems is based on the requirements of UL 300, National Fire Protection Association 17a Standard for Wet Chemical Extinguishing Systems, and the manufacture specifications. Contractors are typically approved by the manufacture of the system to design and install the system based on pre-approved or pre-engineered requirements found in the manufacture requirements.
The suppression system provides nozzles which discharge the suppression agent in the duct work, plenum space, and the cooking surface. Typically all cooking equipment is protected with a specific nozzle configuration except enclosed ovens. The system includes a suppression tank, piping, and nozzles. The size of the tank is based on the number of flow points (typically related to the number and size of the nozzle) located in the system. The number of appliances, size of the hood, and plenum are the basis for the number of nozzles needed. Each manufacture specifies a specific nozzle type and location for a specific cooking appliance. Nozzles are very specific to the manufacture and can are not designed to be interchanged between manufactures.
The systems are activated automatically or manually. Automatic activation is created by a series of fusible links (located in the plenum space over each appliance and duct opening) connected to a releasing mechanism. One the heat reaches the predetermined temperature the link is released which activates the system. The system will discharge through all nozzles until the cylinder is empty. The manual activation is created by pulling a pull station which is located near the hood and on the way to the exit.
The systems are tested by a wet chemical discharge test. The contractor will use a test chemical and activate the system manually or simulate the releasing of a fusible link. The system will then discharge agent through all nozzles which is collected. The inspector should look for leakage at all joints and ensure agent has been discharged through all nozzles. Many communities are accepting a "puff-test" which utilizes air in lieu of an agent.
Dry Chemical Systems
Dry Chemical fire suppression systems utilize a dry chemical which discharge through a series of pipe and terminate in a nozzle. The systems can be classified as total flooding, local application, and can even include hose-line based system. The systems can be found protection fuel pump islands, paint spray booths, and may include special industrial processes. The systems are typically pre-engineered for the hazard they will protect by the manufacture and tested by an approved listing company. The protection of a paint spray booth is a typical application and the manufacture's installation and design instructions will outline the appropriate length or size of pipe, number of elbows or tees, and the type of nozzle for the space. The designer will submit plans for approval within the specifications of the manufacture and include information in accordance with National Fire Protection Association 17 Standard for the Installation of Dry-Chemical Extinguishing Systems.