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You have mass flow rate and velocity, but the area this is spread over will say a lot -

$$\dot{m} v = F = 1 {{kg} \over {s}} \cdot 1,000 {{km} \over {s}} \cdot 1,000 {{m}\over{km}}= 1 \times 10^{6} N $$

If your engine design spreads this over a 2 meter (6.6 ft) diameter (1 m radius), you'd have $$ {{1 MPa} \over {\pi r^2}} \approx 333 kPa$$ 

Compared to atmospheric pressure (101 kPa), three atmospheres is still a lot for unprotected civilians. This relationship scales with $$ {{1}\over{r^2}} $$

Your design for atmospheric operation could double the exhaust area, which would make a tolerable gauge pressure.