Nitrogen acts as a simple asphyxiant by displacing oxygen; when nitrogen in contaminated air rises to about 84 percent or more, oxygen falls to 16 percent or less, causing asphyxia risk.

Introduction / Context:
In confined or contaminated atmospheres, inert gases like nitrogen can displace oxygen without providing warning signs (no odor, no irritation). Such gases are termed simple asphyxiants. The principal hazard is reduction of the partial pressure of oxygen in the lungs, leading to hypoxia and potentially rapid loss of consciousness.

Given Data / Assumptions:

• Normal dry air contains ~78 percent nitrogen and ~21 percent oxygen.
• Asphyxia risk escalates as oxygen drops below about 19.5 percent (commonly used safety threshold), with severe symptoms as it approaches ~16 percent and below.

Concept / Approach:
As nitrogen concentration increases, oxygen decreases proportionally. If nitrogen is 84 percent, oxygen is roughly 16 percent, which is within a dangerous range for workers and bystanders, especially under exertion.

Step-by-Step Solution:

Verification / Alternative check:
Safety standards flag atmospheres with O2 < 19.5 percent as oxygen-deficient. Many incident reports involve inert gas purging or leaks that push O2 near 16 percent or less, rapidly incapacitating entrants.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming symptoms occur only at very low oxygen levels; ignoring rapid onset and lack of warning properties; entering confined spaces without testing.

Final Answer:
84 percent