  Aims. We aim to explain line formation of He I D3 and He I 10830 {\AA} in
small-scale reconnection events. Methods. We make use of a simulated Ellerman
bomb (EB), present in a Bifrost-generated radiative Magnetohydrodynamics (rMHD)
snapshot. The resulting He I D3 and He I 10830 \AA\ line intensities are
synthesized in 3D using the non-LTE Multi3D code. We compare the synthetic
helium spectra with observed SST/TRIPPEL raster scans of EBs in He I 10830 \AA\
and He I D3. Results. Emission in He I D3 and He I 10830 \AA\ is formed in a
thin shell around the EB at a height of $\sim 0.8$ Mm while the He I D3
absorption is formed above the EB at $\sim 4$ Mm. The height at which the
emission is formed corresponds to the lower boundary of the EB, where the
temperature increases rapidly from $6\cdot 10^3$ K to $10^6$ K. The opacity in
He I D3 and He I 10830 \AA\ is generated via photoionization-recombination
driven by EUV radiation that is locally generated in the EB at temperatures in
the range of $2\cdot 10^4 - 2\cdot 10^6$ K and electron densities between
$10^{11}$ and $10^{13}$ cm$^{-3}$. The synthetic emission signals are a result
of coupling to local conditions in a thin shell around the EB, with
temperatures between $7\cdot 10^3$ and $10^4$ K and electron densities ranging
from $\sim 10^{12}$ to $10^{13}$ cm$^{-3}$. Hence, both strong non-LTE as well
as thermal processes play a role in the formation of He I D3 and He I 10830
\AA\ in the synthetic EB/UV burst that we studied. Conclusions. In conclusion,
the synthetic He I D3 and He I 10830 \AA\ emission signatures are an indicator
of temperatures of at least $2\cdot 10^4$ K and in this case as high as $\sim
10^6$ K.
