This is the trap threshold that pairs with cardBTUsNoResource, defining how many BTUs discarded due to a lack of free replacement buffers this card must accumulate within one minute before an alert fires. Because BTU-no-resource events indicate the card's own buffer pool, not the network, is undersized for current traffic, this threshold is how you get warned that a specific card is running out of internal headroom before it starts dropping cells outright. On a card carrying several OC-3 ATM trunks, an admin might set this to 100 so only sustained buffer exhaustion, not a momentary microburst, triggers escalation.