26 Dec The gap that protects

Fahri Yiyin, takes a closer look at the minimum distance between Class I-II-IIIA liquid chemical storage tanks.

According to NFPA 30, flammable and combustible liquids must be classified based on their flash point and boiling point. Liquids with a closed-cup flash point below 37.8°C are categorised as flammable. Considering the boiling point, chemicals with a closed-cup flash point above 37.8°C fall under the combustible category. The aim of this study is to determine the minimum separation distance required between storage tanks containing Class I liquids. The reference standards applied are the UAE Fire and Life Safety Code of Practice and NFPA 30. Examples of chemicals falling under Class I include methyl ethyl ketone, methanol, n-butanol and toluene.

NFPA 30, in Chapter 22, Storage of Liquids in Tanks-Aboveground Storage Tanks, outlines requirements regarding tank-to-tank spacing and the distance between tanks and the nearest structures. Table 22.4.2.1, Minimum Shell-to-Shell Spacing of Aboveground Storage Tanks, groups Class I and Class II liquids under the same category for spacing calculations. For tanks with diameters up to 45 metres, the minimum separation distance between tanks containing Class I liquids is determined by dividing the sum of their diameters by six. For instance, if two chemical storage tanks have diameters of 10 metres and 14 metres, respectively, the minimum separation distance should be calculated as: (10 + 14) / 6 = 4 meters. That calculation also applies to Class II and Class IIIA liquids with diameters less than 45 metres.

For tanks exceeding 45 metres in diameter, if remote impounding is provided in accordance with Section 22.11.1, the sum of the diameters is divided by four. If open diking is provided in accordance with Section 22.11.2, the sum is divided by three. In all cases, the minimum distance between tanks must not be less than 1 metre. Provisions for LPG storage and tank pressures are addressed separately in Section 22.4 of NFPA 30.

In the UAE Fire and Life Safety Code of Practice, Chapter 13 is dedicated to flammable and combustible liquids. Section 2.1.5 specifies that NFPA 30, NFPA 30A and the NFPA 30 Handbook are adopted as reference documents. In Table 13.4.g, Minimum Shell-to-Shell Separation Distance between Storage Tanks, the spacing requirements align closely with those of NFPA 30, whereby the tank diameter and the classification of the stored liquid determine the minimum required separation.

This feature appeared in issue 68 of Fire Middle East magazine.