When managing an open (compound) limb fracture where broken bone ends protrude through the skin, what critical mistake must first responders NEVER commit?

1. Never cover the protruding bone with sterile dressings
2. Never attempt to push or force the protruding bone ends back beneath the skin, as this introduces contaminated road bacteria deep into the bone marrow causing osteomyelitis
3. Never call 120 emergency services
4. Never check the patient's distal pulse in the fingers or toes