**Core Concept**
Circulatory collapse or shock in adults occurs after severe burns, which compromise the body's ability to maintain blood volume and perfusion. The extent of burns is measured by the total body surface area (TBSA) affected, and different percentages of TBSA burns are associated with varying degrees of systemic response and risk of complications.

**Why the Correct Answer is Right**
The correct answer, 15% TBSA burns, is associated with a significant risk of circulatory collapse due to the loss of fluid and electrolytes through burned skin, leading to hypovolemic shock. This is because the body's compensatory mechanisms are overwhelmed by the extent of the injury, resulting in decreased cardiac output and peripheral perfusion. The loss of fluid through the burned area also leads to hemoconcentration, which exacerbates the risk of thrombosis and further compromises perfusion.

**Why Each Wrong Option is Incorrect**

**Option A:** 5% TBSA burns is typically considered a minor burn injury and is usually not associated with systemic complications or circulatory collapse. Patients with burns of this extent can often be managed conservatively without significant interventions.

**Option B:** 10% TBSA burns may result in some systemic complications, but the risk of circulatory collapse is still relatively low. Patients with burns of this extent may require fluid resuscitation and monitoring, but the risk of shock is not as high as with 15% TBSA burns.

**Option D:** 20% TBSA burns is an extremely severe injury that is associated with a high risk of circulatory collapse, multiple organ failure, and death. While this answer is not the minimum percentage associated with circulatory collapse, it is a more accurate reflection of the severity of the injury.

**Clinical Pearl / High-Yield Fact**
The Parkland formula, which estimates the volume of fluid required for resuscitation in burns patients, is as follows: 4 mL/kg/%TBSA burned in the first 24 hours, with half of this volume administered in the first 8 hours.

**✓ Correct Answer: C. 15%**