  A dramatic development occurring in our daily life is the increasing use of
mobile equipment including mobile phones and wireless access to the Internet.
They enable us to access several types of information more easily than in the
past. Simultaneously, the density of mobile users is rapidly increasing. When
hundreds of mobile phones emit radiation, their total power is found to be
comparable to that of a microwave oven or a satellite broadcasting station.
Thus, the question arises: what is the public exposure level in an area with
many sources of electromagnetic wave emission? We show that this level can
reach the reference level for general public exposure (ICNIRP Guideline) in
daily life. This is caused by the fundamental properties of electromagnetic
field, namely, reflection and additivity. The level of exposure is found to be
much higher than that estimated by the conventional framework of analysis that
assumes that the level rapidly decreases with the inverse square distance
between the source and the affected person. A simple formula for the exposure
level is derived by applying energetics to the electromagnetic field. The
formula reveals a potential risk of intensive exposure.
