Zone classification for sewage storage and packing system

[seuenergy]

Hi all,

We have one storage house for sewage. The design engineer want to classify the house as zone2 as there might be slight H2S generated by sewage.
As the house is equiped with forced ventilation( not sure if the ventilation rate reaches 6 times per hour), I can not argue with this zone 2 decision.
But I am wondering how much H2S could be generated by sewage to form an explosion environment? Does any one have some information for this? Thanks!

 

[shvet]

1/ Descrbe the sewage. Describe the house.
2/ What about underground sewer system and pump station - is it designed Ex-proof or not? Is the sewer system segregated?
3/ What is the sources of water? Is it process drains or a surface water drainage?
4/ Why H2S? Why not CH4 or HC?
5/ Do you understand that H2S acute toxicity threshold is much lower than LFL? One will definetly die from intoxication prior being exploded.
6/ What for is sewage stored and packed?
You need to share much more details related to obtain a valuable reply whether you concerns are real or not.

For info - whether water can exlode

Use of Nitrogen Purging - Petroleum engineering general discussion

Can someone tell me, if nitrogen purging is required for hydrocarbon lines only or if it also required for fire water lines / tanks as well?

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EI 15

3.6.5 Surface water drainage systems
Oily water and chemical sewers can become contaminated with flammable fluids during normal operations, and openings to atmosphere should therefore be regarded as sources of primary grade release.
Normal open surface liquid drain channels, typically not more than 0,5 m wide, handling flammable materials should have a nominal hazardous area of 1 m horizontal radius each side and 1 m radius vertically above them. Where there is a possibility that a hot material (e.g. category C fluid above 50 °C or steam condensate) could enter the drain in sufficient quantities to produce an appreciable flammable vapour, or that category A or B materials could inadvertently enter, these distances should be extended to 3 m.
The vaporisation rate from any vents on drain systems should normally be low and a Zone 1 hazardous area should be drawn in accordance with Table 3.2 assuming a vent rate of not more than 10 m3/hr at ambient conditions.
The possibility of abnormal releases (e.g. hot water) entering the drains and the vaporisation of volatile liquids should be considered. Based on this it may be appropriate to define a larger Zone 2 area for the vent using dimensions given in Table 3.2 consistent with the higher vapour emission rate.
The possibility of vapour release should always be considered when access chamber covers are lifted or temporarily removed.
Note: Drainage systems for distribution installations should be designed with consideration given to the principles detailed in EI Model code of safe practice – Part 2: Design, construction and operation of petroleum distribution installations and EI Environmental guidelines for petroleum distribution installations. In the case of filling stations, the design should give consideration to the principles detailed in APEA/EI Design, construction, modification, maintenance and decommissioning of filling stations.