is it essential to teach an emergency ascent in open water sessions (SSI standards) ?
Teaching by SSI's standards, yes, it is required to teach both the Emergency swimming ascent (in both pool & Open Water) & the Emergnecy buoyant ascent (pool only). When I teach these I teach these techniques with the understanding that these are the least desirable methods to deal with an OOA situation (the most desirable techniques being watching your gauge/ following gas planning to avoid the situation altogether & if there is a need,.. to share air to get to the surface safely) & that it could increase the risk of DCS.