In the moments before the cargo ship Dali rammed into the Francis Scott Key Bridge and sent it crumbling into the water, a flurry of urgent warnings crackled over radios and enabled police to block traffic from getting on the span, likely saving lives.

But those warnings seemingly didn’t reach the six construction workers who were killed in last week’s collapse of the Baltimore bridge. Their deaths have raised questions about whether the construction company took proper precautions, including keeping a safety boat nearby that might have been able to warn them at least a few seconds before impact.