2.3.2 Explosive Mixtures

Precautions to prevent the formation of explosive and flammable vapour-air mixtures have the highest priority in the handling, storage and transport of ethylbenzene. In order to eliminate or minimize this hazard, ethylbenzene containers or vessels are blanketed with an inert gas, such as nitrogen, or a reduced loading speed is applied to air filled containers.

The explosion limits in air (at atmospheric pressure, measured at 140 °C) are:

• Lower Explosion Limit (LEL): 1.2 %vol.
• Upper Explosion Limit (UEL): 8.0 %vol.

Explosive vapour-air mixtures in tanks will be prevented either by maintaining the temperature below the flash point in the liquid and vapour space (by application of a safety margin of a few °C) or by blanketing the vapour space with nitrogen or another inert gas. When working under inert gas conditions it must be ensured that the oxygen level remains below 8 % so that the vapour phase remains out of the explosive range.

When tanks are inerted, it is of utmost importance to consider that such an oxygen deficient atmosphere is life threatening, as it poses the additional hazard of asphyxiation. Tank entry without air supplied respirators and proper protocols in place should be forbidden. Even inspection of the tanks from the tank hatches is considered dangerous.

Ethylbenzene can form a combustible mixture with air at rather low temperatures, and therefore the necessary precautions must be taken, e.g. use appropriate design codes, and follow-up on the condition by inspection methods, repair leaks immediately, ensure that handling areas are well ventilated and install proper facilities to remove spills quickly.

It is recommended that vapours are not blown off directly to the atmosphere, but that these are routed back to the manufacturing process or routed to a vapour treatment unit. The vapour lines should be adequately protected against flame propagation.

Storage tanks and product containers that have been emptied must be flushed with water and/or steam, followed by nitrogen, and subsequently air to remove ethylbenzene vapour before they can be worked on with welding equipment or entered. Before entering a storage tank that has been flushed with nitrogen, an appropriate measurement device should be used to check for sufficient oxygen. To ensure proper measurements, any forced ventilation should be stopped. . Always sample at the bottom side of the container as ethylbenzene vapours are heavier then air and will accumulate at the bottom.

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Patrick Detournay
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