The Blast Lung Injury Severity Score (BLISS) is calculated from three domains, each assigned points based on published severity groupings:

PaO2/FiO2 (mmHg): >200 = 0 points. 60–200 = 2 points. <60 = 4 points.
Chest x-ray infiltrates: localised infiltrates = 1 point. bilateral or unilateral infiltrates (not massive bilateral) = 2 points. massive bilateral infiltrates = 3 points.
Bronchopleural fistula: present = +1 point. absent = 0 points.

Total BLISS Score = sum of domain points (typical range 1–8). Higher scores reflect more severe primary blast lung injury.

Classic severity patterns described in the literature can be summarised as:

Severity	PaO2/FiO2 (mmHg)	Chest radiograph	Bronchopleural fistula	Typical ventilatory needs
Mild	>200	Localised lung infiltrates	Absent	Usually does not require mechanical ventilation. If ventilated, low PEEP (≤5 cmH2O).
Moderate	60–200	Unilateral or bilateral infiltrates	May be present or absent	Conventional ventilation commonly required. PEEP around 5–10 cmH2O.
Severe	<60	Massive diffuse bilateral infiltrates	Present	High PEEP (>10 cmH2O) and often unconventional strategies such as inverse-ratio ventilation, high-frequency jet ventilation, independent lung ventilation, inhaled nitric oxide, or ECMO.