Many things hit an explosive atmosphere at around 4%. Also, there is the concept of deflagration vs detonation, the latter being decidedly worse, but unlikely

Many things hit an explosive atmosphere at around 4%. Also, there is the concept of deflagration vs detonation, the latter being decidedly worse, but unlikely in this case due to the geometry. There is a whole field of electrical engineering dedicated to defining potential for and avoiding of igniting explosive atmospheres in industrial plant.