Rather than putting phosphine in the headspace, some silos are equipped with a ground application system. Phosphine is applied into a chamber at ground level and disperses’ through the grain via an opening into the bottom of the silo and/or via a sealed recirculation system. The important thing is that the phosphine has a large space in the application chamber and/or room to disperse freely into the grain so the gas concentration doesn’t reach explosive levels in the confined space. For more on phosphine application see ‘Grain fumigation – a guide or ‘Fumigating with phosphine, other fumigants and controlled atmospheres