Not all changes can be incorporated into the directive without testing them on a real-life scale. This is why VdS planned, organized, conducted and evaluated its own fire and extinguishing tests in September 2022. In order to gain as much knowledge as possible from the tests, it is important to define precise objectives and questions at the outset.
The main objective of the tests is to determine the maximum distance between the face sprinklers and the outer edge of the shelving or any stored goods that may protrude from the shelving. In section 11.6.1.1 of VdS CEA 4001, a maximum distance of 200 mm from the outer edge of the stored goods is permitted, whereby the face sprinklers may be located both above the stored goods and in the cross shaft. In other regulations, larger distances of up to 600 mm are also permitted, but with the restriction that the face sprinkler must be located in the cross shaft.
Another difference to other regulations is the type of water-permeable boxes approved by VdS. The various water-permeable boxes differ in whether they have openings in the base or in the side, whereby both are possible according to VdS CEA 4001. In addition, the advantages of water-permeable boxes described in section K.7.1 are to be verified by comparative tests with water-impermeable boxes.
The third aim of the fire and extinguishing tests is to check whether it is possible to simplify the hydraulic calculation of sprinkler systems in automatic small parts warehouses. At the moment, each line (max. 3) must provide the required water coverage on its own, i.e. 3 lines of 45 m2 each.
The questions are tested using a partial section of an automated small parts warehouse on a real scale. The test setup comprises two shelves, placed against each other at the back, with a width of 3.00 m (6 crates), a depth of 1.23 m each (2 crates) and a height of 4.40 m (8 crates), see illustration. The top edge of the stored goods is at a height of 4.05 m. Boxes measuring 600 mm x 400 mm x 220 mm can be stored in this rack.
The crates used vary between double-walled and single-walled as well as water-permeable and water-impermeable, whereby the water-permeable crates are divided into “water-permeable bottom (u)” with openings in the base area and “water-permeable side (s)” with openings in the lower area of the side walls. According to VdS CEA 4001, section K.7.1, openings in the base and/or in the side walls are permitted. An exemplary arrangement is given with 12 openings with a diameter of 5 mm evenly distributed in the base of the container. According to FM data sheet 8-34, only openings of at least 30 % of the wall area within 13 mm vertical distance from the inner bottom of the container are permitted.
| double-walled | single-walled | water-permeable | water- and permeable | 200 mm indented | 400 mm indented | Ignition down | Ignition top | |
| Attempt 1 | X | X | X | X | ||||
| Attempt 2 | X | X | X | X | ||||
| Attempt 3 | X | X (u) | X | X | ||||
| Attempt 4 | X | X (s) | X | X | ||||
| Attempt 5 | X | X | X | X | ||||
| Attempt 6 | X | X | X | X | ||||
| Attempt 7 | X | X (u) | X | X |
Fig. 3: Test variations
The installed sprinkler system comprises two sprinkler levels with face sprinklers (red) and sprinklers in the central shaft (green), which are located at a height of 1.64 m and 3.60 m, see illustration. The horizontal distance between the sprinklers is 1.00 m. The face sprinklers are offset centrally to the sprinklers in the middle shaft and all sprinklers in the first sprinkler level are offset centrally to the sprinklers in the second sprinkler level. The sprinklers used are flat screen sprinklers K57, pendant, RTI < 50, with a trigger temperature of 68 °C. The distance between the sprinkler spray discs and the top edge of the boxes is 100 mm. The face sprinklers are positioned centrally above the crates with the variation that they can be positioned at a distance of 200 mm or 400 mm from the outer edge of the stored goods.
Temperature measuring points are provided on each sprinkler as well as centrally above the crate on the outer edge of the shelf and 600 mm indented. In addition, one temperature measuring point is not positioned centrally above the crate, but indented 600 mm from the outer edge of the shelf in the cross shaft.
The test series comprises seven tests that differ in the type of boxes and the position of the face sprinklers, see table. In addition, it is checked whether a change in the ignition position from the lowest box level to the box level directly above the first sprinkler level is likely to cause a secondary fire due to dripping plastic (test 6). The boxes are empty in six tests and filled with air-permeable wood in one test in order to also test the influence of filled boxes (test 7). The evaluation criteria for the tests include the measured temperatures, the number and time of open sprinklers and the existing fire damage after manual extinguishing following the test period.
In the first four attempts, the face sprinkler was 200 mm indented, in the fifth attempt 400 mm. In this fifth test, no sprinkler was triggered and the fire was extinguished manually 30 minutes after ignition. The examination of the temperature distribution showed that the thermocouple, which was indented 600 mm (T3-5) but was located in the cross shaft, measured a higher temperature early on than the thermocouple on the sprinkler, which was indented 400 mm (T1-5), see figure.
From five minutes after ignition until 20 minutes after ignition, a temperature of around 100 °C was continuously present at the thermocouple in the shaft, which would have triggered a sprinkler installed there. The temperature at the thermocouple on the sprinkler closest to the ignition source fluctuated around 60-70 °C, but this was not sufficient to trigger this sprinkler.
The test results show that the distance of 200 mm between the face sprinkler and the outer edge of the stored goods is already maximum, regardless of shafts, and cannot be increased any further. An arrangement of the face sprinklers in the shaft may be more favorable.
Water permeability of the storage tanks
The comparative tests between water-impermeable crates (test 2) and water-permeable crates with openings in the base (test 3) showed no significant differences in either the temperature distribution or the resulting fire damage. The temperature distribution at the first triggered sprinkler of the two tests is shown in Figure 5, and a comparison of the fire progression is shown in Figure 6. A comparison of water-permeable boxes with side openings (Test 4) or openings in the floor (Test 3) also showed no significant differences in the fire progression after triggering of the first sprinkler or in the fire damage caused. The fire progression of these tests is shown comparatively in Figure 7. In tests 2, 3 and 4, only one sprinkler opened in each case. Advantages for water-permeable boxes in accordance with VdS CEA 4001, Section K.7.1 cannot be confirmed by the tests.
Spread could always be prevented
In none of the tests carried out in accordance with the applicable VdS CEA 4001, i.e. with an indented face sprinkler of maximum 200 mm, did more than three sprinklers open to control the fire, and in none of the tests did the fire spread via the center shaft to the rear of the rack, so that further spread could always be prevented. Even the control test, in which the fire was ignited in the box above the first sprinkler level, did not result in a secondary fire below the ignition level. During this test, burning plastic dripped into a box below the first sprinkler level, but this fire was completely extinguished by an open sprinkler, so that no further spread occurred here either. Based on these test results, it is possible to reduce the effective area in the automatic small parts warehouse to 90 m2 or 2 lines of 45 m2 each.
The series of tests carried out enabled a number of questions relating to the protection of automatic small parts warehouses to be answered. In principle, it was confirmed that the VdS concept for the protection of small parts warehouses with K57 sprinklers - which international regulations do not recognize - is effective.
Further results are:
- A maximum face sprinkler indentation of 200 mm is possible with a shaft-independent arrangement.
- If the sprinklers are arranged in the cross shaft between the load carriers, they will also be triggered if the indentation exceeds 200 mm.
- The close sprinkler arrangement prevents the fire from spreading horizontally in the rack. A hydraulic calculation of two lines per sprinkler level with 45 m2 each is therefore sufficient.
- Water-permeable boxes have not shown any significant advantage in the course of the fire.
The results mentioned will be discussed further and will have an impact on the next edition of VdS CEA 4001 in January 2024.