Research in the USA and Europe has shown that explosion proof seals can be made from a variety of materials and designs, but are generally built to suit availability of material, and are over designed, with actual designs based on trial and error. Explosion proof seals are generally defined as capable of withstanding pressures of 20 psi, but have been tested at pressures above 300 psi.
The US regulations concerning the construction of seals are based on the long-term explosion research programmes carried out by MSHA, and in particular the more recent work during the 1990’s at the Lake Lynn facility.
Regulations state that a seal must withstand a static horizontal pressure of 20 psi and although there are construction details given, any alternative construction is permitted if it meets this pressure requirement, and is fire retardant.
In addition to the pressure requirement, MSHA have air leakage guidelines that a seal must withstand after an explosion, and recommend it should maintain its operation for a minimum of one hour after an explosion.
Approval of seals is by full scale explosion testing at Lake Lynn, where seals are exposed to explosions producing 20 psi (140 kPa), and then tested for leakage.
Australian approved standards for ventilation control do not address the structural design or material requirements for seals, but also require an overpressure of 140 kPa, and this within 24 hours of construction.
Approved systems for seal construction from MSHA are concrete blocks, Omega 384 foam blocks, cementitious foam seals and polymer foam seals. These all have approved methods of construction.
There are no effective small scale tests, or non destructive in situ tests for designs, materials or existing seals. Further work should be carried out to investigate small scale testing, and an evaluation method for existing seals.
The US definition of explosion proof seals is limiting, and ensures an effective one hour operation of a seal post-explosion. This needs to be further considered for South African application, and whether the seal must maintain the mine operations as well as provide escape time.