Modern sprinkler design comprises multiple responsibilities, including those of the estimator, project engineer, project manager, and quality control. The layout technician plays a crucial role. A layout technician’s profession might start with a high school diploma and lead to a key job in the fire sprinkler industry. With proper training and guidance, a new layout technician can become a valuable member of the team.
Successful fire sprinkler setup technicians must understand NFPA 13 and its criteria. This essay intends to provide a primer for layout technicians at the beginning of their careers or those interested in pursuing this rewarding sector.
At first sight, NFPA 13 can be intimidating. Breaking down the standard into smaller components makes it easier to understand. The 2022 edition of NFPA 13 has 32 chapters and six annex chapters.
Local ordinances and codes must comply with NFPA 13’s 32 chapters. The annex material is intended for informational purposes and cannot be enforced unless specifically accepted by the relevant authorities.
This assessment is subsequently forwarded to the layout technician. Although it is not a technician’s responsibility, understanding this stage is crucial for the layout and design process.
The danger level evaluation criteria are divided into two categories: storage and non-storage. Storage areas are further categorised into three different categories: Miscellaneous storage Low. Pile storage and high-piled storage. This essay focuses on fundamentals and will not go into detail about storage criteria.
The table below explains each occupancy classification and includes examples of facilities that fall under each category. Annex Section 4.3 provides a comprehensive list of examples for each occupation.
- The maximum protection area varies according to construction and system type. Table 10.2.4.2.1(a) provides a detailed breakdown of protection areas for Light occupations.
The maximum protection area and sprinkler spacing vary depending on the system type Table 10.2.4.2.1(c) provides a detailed analysis of protection areas for Extra occupations.
The maximum protective area limits sprinkler spacing. For an ordinary occupancy classification, the maximum sprinkler spacing is 15 feet. Sprinklers set 15 feet apart in one direction are limited to 8 feet and 8 inches in the perpendicular direction to maintain a maximum protection area of 130 square feet. The “S X L rule” is used to determine the distance between sprinklers along branch lines, whereas L denotes the distance between sprinklers on neighbouring branch lines.
To meet the maximum protection area, multiplying the distance (S) by the distance (L) should not exceed the set limit. Additionally, sprinklers only cover half of the space (L or S) between them. As a result, the distance to walls is limited to half the distance in that direction (i.e., 1/2 S or 1/2L). For more detail contact Rotaflow team.
Sprinklers must be correctly spaced for adequate coverage, but obstructions such as objects or structural parts might hinder their effectiveness. NFPA 13 identifies these as obstacles. Obstructions near sprinklers have a greater impact on their performance. NFPA 13 distinguishes between two types of obstructions: those that hinder pattern development (18 inches below the sprinkler deflector) and those that prevent sprinkler discharge from reaching the hazard (18 inches or more below).
As previously mentioned, there are two factors that can affect the degree of a blockage. Obstacles increase with size and proximity to the sprinkler. According to Section 10.2.7.3.1.3, sprinklers must be spaced at least three times the largest diameter of the blockage. This section is commonly known as the “3 Times Rule.”. This regulation is only applicable to horizontal impediments within 24 inches of the sprinkler and vertical impediments.
Obstructions can occur at any distance. Even in well-coordinated projects, appliances are often placed.
The lack of representation in plans makes it difficult to predict probable obstacles using the three-time rule. In light and ordinary hazard occupancies, the regulation only applies to structural elements. You can learn about it in Lunch and learn session with Rotaflow team.
The 2022 edition provides guidelines on vertical obstacles in ordinary hazard occupancies (Section 10.2.7.3.2.3).
Obstructions located more than 18 inches below the sprinkler have less strict regulations. Sprinkler protection must extend to the area below fixed impediments over 4 feet wide, as per Section 10.2.7.4. The Duct Rule only applies to fixed impediments; thus, conference tables, for example, do not need sprinklers. This restriction does not apply to non-combustible impediments over 4 feet and less than 24 inches from the floor.
Sprinkler types, including sidewall, extended coverage, CMSA, and ESFR, have specific obstruction regulations outlined in their installation chapters.
NFPA 13 specifies both the minimum sprinkler density and the design area for calculating sprinkler flow. NFPA 13 uses the design area rather than an estimated fire size or testing results to determine the number of sprinklers required in a fire for a particular occupancy classification. Table 19.2.3.1.1 in NFPA 13 contains the densities and required areas of operation for each occupancy classification. A summary is provided below.
Courtesy: Jeff, P.E., Fire Protection Engineer for the NFSA.
