Maybe the attached diagramm helps

You should made the 1/3-octave spectrum of measured vibrations (accelerations). Than the spectrum can be compared with the line of exposition time according to ISO 2631. 

Using Matlab you can define it as follows:

%>>>>>>>

%reduced physical efficiency limit (8h)

xu=[0.71 0.63 0.56 0.5 0.45 0.4 0.355 0.315 0.315 0.315 0.315 0.4 0.5 0.63 0.8 1.0 1.25 1.6 2 2.5 3.15];

%exposure limits (8h)

xsz=2*xu;

%reduced comfort limit (8h)

xk=xu/3.15;

%frequency vector

cz=[0.8 1.0 1.25 1.6 2.0 2.5 3.15 4.0 5.0 6.3 8.0 10.0 12.5 16.0 20.0 25.0 31.5 40.0 50.0 63.0 80.0];

figure;

loglog(cz,xsz,'r');

xlabel('Frequency [Hz]');

ylabel('RMS value of the vertical acceleration [m/s^2]');

hold on;

loglog(cz,xu,'m');

loglog(cz,xk,'g');

%loglog(ff,P1); here you own vector can be ploted

aac=legend('exposure limits (8h)','reduced physical efficiency limit (8h)','reduced comfort limit (8h)');

grid on;

zoom on;