Foam

What is a Nozzle Aspirated Foam System (NAFS)?

Authored By Dominic Colletti
Date September 21, 2022
Authored By Dominic Colletti
Date September 21, 2022
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Nozzle Aspirated Foam Systems (NAFS) 

To produce finished foam for application onto fire, four basic items are required: water, foam concentrate, air, and mechanical agitation. When all four components are brought together in the correct amounts, finished foam (the media applied to the fire or fuel surface) is produced. 

Nozzle Aspirated Foam Systems (NAFS) have been used by firefightrs for many decades. They add air at the nozzle device. Mechanical agitation needed to produce finished foam occurs via the nozzle spray pattern entraining air, or via a foam tube attachment.  

Parts of a NAFS System 

Components of a NAFS typically include a water supply, fire pump, foam proportioner, and nozzle. For example, a typical pumper uses its booster tank water supply, an in-line eductor, hoseline, and air aspirating nozzle.  

How a Nozzle Aspirated Foam System Works 

To create finished foam, water is first moved to the eductor inlet by a fire pump. The eductor siphons in, or proportions, a specific amount of foam concentrate with the water.  This action creates foam solution. The foam solution is pumped through the attack hose to the nozzle, where air and mechanical agitation take place and finished foam is created.  

So, with NAFS, the nozzle device is used to introduce air to create finished foam. Examples of NAFS include fixed gallonage or automatic fog nozzles, air aspirating foam tube nozzle attachments and high-expansion foam generators. Each of these introduce different volumes of air into foam solution and provide different levels of mechanical agitation to create various finished foam blanket qualities. 

Foam quality is measured by expansion ratio and foam blanket drain time. Expansion ratio and drain time directly affect fire suppression performance of finished foam.  

NAFS Example: Quadracup 

 

The selectable flow TFT Qudracup is an example of a NAFS. When the outer sleeve is in the retracted position, the nozzle operates the same as a selectable gallonage nozzle. Flow can be set to any one of four flow settings 30-, 60-, 95- or 125-gpm, or to the flush mode.  

The front end can be rotated from straight stream through wide fog patterns. To use the built-in foam aspirating feature of the nozzle, the nozzle operator slides the outer sleeve forward, and by adjusting the pattern, has control of reach and aspiration of the finished foam. If an immediate wide fog pattern is needed, the sleeve can be retracted instantly to its regular position. This device produces low expansion finished foam. 

Conclusion 

As you can see, a NAFS option has been used for decades and is a simple setup for foam delivery. But this option may not address all your needs. Some departments utilize a compressed air foam system (CAFS) to deliver a high-quality firefighting foam blanket.  

Get an introduction to CAFS with this article