## 2 Materials and Methods
### Application of the Proposed Method in Practice  
The main reason for these measurements is to assess the acoustic risk by measuring the noise exposure levels \(L_{A}\) and \(L_{Z}\) and to show the influence of acoustic energy on the extra-auditory effects of employees exposed to this type of noise. Measurements were carried out at four engineering workplaces in seven work activities. Measurements of LFN in W1-W4 machinery workplaces at individual WA1-WA7 work activities took place during the performance of individual work activities in the workplaces. The marking of individual workplaces and work activities is outlined in Table 4. The measured quantities (A-sound pressure level \(L_{A}\) [dB]; Z-sound pressure level \(L_{Z}\) [dB]) were then applied to the proposed CMARA method. Thus, two experimental measurements were performed in succession in each workplace during work activities WA1-WA7. Figure 2: The acoustic risk management algorithm. Source: own research (inspired by 12100 [29]). A Bruel & Kjaer type 2250 manual sound analyzer was used for each measurement of the LFN and its evaluation. The noise load measurements were carried out in accordance with the standard. For working conditions of individual work activities, a strategy of working task (operation) measurement was applied. The measured values of \(L_{A}\) and \(L_{Z}\) were considered at low frequencies, from 16 Hz to 100 Hz. The summary results of the measurements of noise exposure during the time of work activities of WA1-WA7 using two types of weighing filters are presented in Figure 3, including measurements using an A-weighting filter. In Figure 4, the results of the measurements using a Z-weighting filter are given. The measurements of noise load during individual work activities indicate that low-frequency acoustic waves have significantly higher values using the Z-weighting filter than using the A-weighting filter. The difference between \(L_{Z}\) and \(L_{A}\) decreases with increasing frequency, as evidenced by the resulting differences during WA1-WA7. The measured higher values of acoustic energy emissions and their long-term effects on employees could not only affect the auditory organ but also exert significant effects on other systems. The steps of application of the proposed method for the assessment of acoustic risks at low frequencies are as follows:  
1. The limit values \(L_{Z}\) at frequencies ranging from 16 Hz to 100 Hz are determined based on individual measurements for the factor Probability \(Pna\). The limit value for a high probability \(Pna\) is the average value from individual measurements. From it derives the medium probability, and consequently the low probability \(Pna\). 2. The duration of the work activity, the factor exposure \(Ex\), is determined when the employee is potentially exposed to LFN during work, shown in Table 5.
3. The degrees of the probability factors \(Pa\) (Table 6) and \(Pna\) (Table 7) are determined according to the measured values at individual frequencies from 16 Hz to 100 Hz. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Workplace** & **Marking of Workplace** & **Work Activities** &
\begin{tabular}{c} **Marking of** \\ **Work Activities** \\ \end{tabular} \\ \hline Workplace of CNC milling & W1 & CNC milling & WA1 \\ Workplace of electrotechnical production & W2 & Tool shop—machining & WA2 \\  & & Spot welding & WA3 \\  & & Welding & WA4 \\ Workplace of steel structures production & W3 & Grinding & WA5 \\  & & Bending & WA6 \\ Woodworking workplace & W4 & Grinding & WA7 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Marking of workplaces and work activities. Source: own research. Figure 3: Levels \(L_{A}\) during WA1-WA7 at the considered frequencies. Data on the already-applied measures are determined before the LFN at individual workplaces W1-W4. Personal protective equipment for hearing protection is used by workers at WA4, WA5, WA6, and WA7. Structural measures were applied to W3, namely noise barriers. Organizational measures have even been applied to W4 and WA7.