- Author
-
Holmstedt, G. L.
|
Ondrus, I.
- Title
- Risker for brand och explosion efter vatskespill i dragskap. [Risk of Fire and Explosion After a Vapor Spill.] (Abstract in English)
- Coporate
- Lund Univ., Sweden
- Report
-
LUTVDG/TVBB-3054,
February 1991,
34 p.
- Keywords
-
explosions
|
fire tests
|
acetone
|
diethyl ether
|
ethanol
|
methyl ethyl
|
ketones
|
ventilation
|
heat detectors
|
sprinklers
- Abstract
- Experiments with vaporizing of liquid spillage of acetone, diethyl ether, ethanol and methyl ethyl ketone and distribuiton of combustible vapor in a fume-cupboard performed with an entrance velocity of ca 0.5 m/s proved that: the amount of vaporized liquid after liquid spillage at different initial temperatures can be predicted with good precision by available computer programs; during spillage the heavy vapor remains in the lower part of the fume cupboard (≤ 10 cm) and is sucked out almost completely through the lower air gap in the fume-cupboard; the liquid spillage which spreads over most of the surface of the fume-cupboard's botton gives rise to such a high local concentration of gas that 25% of the lower flammability limit is exceeded in the smaller air gap in the back of the fume-cupboard as well as in the ventilation channel directly behind the fume-cupboard, even with very large ventilation flow; by decreasing the surface of the spillage, especially in depth, the local concentration of gas can reduce considerably; inside the fume-cupboard there is no risk for concentration of heavy gases which exceed 25% of the lower limit of flammability on the heights above 10-20 cm from the botton surface of the fume-cupboard. Fire experiments in the fume-cupboards after spillage of acetone, ethanol and heptane in the fume-cupboard proved that: the inspected fume-cupboard has good fire resistance and is able to stand several minutes of fire in liquid spillage; a fire in a liquid spillage will be almost immediately controlled by ventilation flow; in a large ventilation flow most of the flames are sucked out through the lower gap in the bottom of the fume-cupboard; if the fire continues for some minutes with a large ventilation flow the ventilation system will be seriously damaged; closed ventilation flow gives the slowest fire development; heat detectors (grade 2 and 3 with activating temperature 58 deg-60 deg C) placed on the vertical back wll of the fume-cupboard ca 1 m from the bottom file activated within 10 s after the start of fire in all of the experiments; the same heat detectors, when placed in ventilation channel 2 m from the fume-cupboard, activated within 20 s when ventilation flow level was 100 m3/h per running meter and within a few seconds when ventilation level was 600 m3/h per running meter; water sprinkling (the sprinkler mounted on the roof of the fume-cupboard) with 10-20 1/m2 per minute is a poor suppression alternative. During sprinkling, in most of the cases the fire continues for one minute after the sprinkler had been activated. There is even risk that, because of the sprinkling, the fire will spread from the fume-cupboard on to the floor outside the fume-cupboard; carbon dioxide supplied by protable fire extinguishe at the lower part of the fume-cupboard's opening extinguishes the fire within few seconds only. The amount of carbon dioxide which was used for fire extinction was less than one kilogram. Two explosion experiments with the fume-cupboard showed that: the fume-cupboard is able to stand an explosion after a delayed ignition of a spillage of 1 liter diethyl ether without cracking of glass in the opening of the fume-cupboard; the release of pressure takes place partly at a downward angle through the opening of the fume-cupboard (5 cm) and partly upwards through the opening for light (0.64 x 0.2 m) in the roof of the fume-cupboard. During the experiments the opening was covered with a 10 mm thick aluminium sheet, which was laid, unattached, over the opening for light.