## 2 Materials and Methods  
### A Proposal for Risk Assessment of Low-Frequency Noise  
A proposed method for assessing acoustic risk at low frequencies (CMARA), is the modification of the mixed risk assessment method set out in ISO/TR 14121-2 [28]. The basis of this method follows the risk assessment algorithm regarding harmonized standards for machinery construction ISO 12100 [29]. The mixed method serves to quantify parameters that are qualitative, combining a risk matrix and numeric score. The resulting value of the risk is calculated by combining the \(Se\) severity parameters (severity of possible damage as a result of the identified hazard, consequences) and \(Cl\) category (1, 2). The overall \(Cl\) probability is given by the sum of the factors, and each factor is estimated independently. The factors include \(Ex\) (exposure, mean interval between exposure frequency and its duration; it is evaluated by the interval length between exposures), \(Pr\) (probability of occurrence of a dangerous event), and \(M\) (possibility to prevent or limit damage). The risk is then evaluated using the risk matrix located in the middle of the rating table of the method. In case of undesirable (high) risk, it is necessary to take protective measures to reduce it. If the risk is acceptable (medium), taking protective measures to reduce the risk is recommended, and at an acceptable (low) risk, it is already reduced enough. Table 1 contains a description of the factors of the proposed method. The factor of the Severity (\(Se\)) is tailored to the consequences of exposure to LFN. The factor has four degrees, namely severe consequences (based on medical examinations), moderate consequences (subjective complaints of workers at and after exposure to noise), minimal consequences (consequences that are only momentary, do not persist after leaving the job and disappear quickly), and negligible to no consequences. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Factor** & \multicolumn{2}{c}{**Description of Factor Levels**} & **Rating** \\ \hline \multirow{6}{*}{_Severity (Se)_} & Severe consequences (based on medical examinations) & 5 \\ \cline{2-3}  & Moderate consequences (subjective complaints of workers at and after exposure to noise) & 3 \\ \cline{2-3}  & & Minimal consequences (consequences that are only momentary, do not persist after leaving the job and disappear quickly) & 1 \\ \cline{2-3}  & Negligible to no consequences & 0 \\ \hline \multirow{6}{*}{Exposure (Ex) Exposure describes how long an employee is exposed to LFN} & More than 6 h and less than or equal to 8 h & 4 \\ \cline{2-3}  & More than 4 h and less than or equal to 6 h & 3 \\ \cline{2-3}  & More than 2 h and less than or equal to 4 h & 2 \\ \cline{2-3}  & Less than or equal to 2 h & 1 \\ \cline{2-3}  & High—point evaluation from 8–12 & 5 \\ \cline{2-3}  & Medium—point evaluation from 4–7 & 3 \\ \cline{2-3}  & Less than—point evaluation less than 3 & 1 \\ \cline{2-3}  & High—point evaluation from 8–12 & 4 \\ \cline{2-3}  & Medium—point evaluation from 4–7 & 2 \\ \cline{2-3}  & Less than—point evaluation less than 3 & 1 \\ \hline \multirow{2}{*}{_Measure (M)_ Application of measures to reduce LFN} & Applied & 0 \\ \cline{2-3}  & Not applied & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Factors of the proposed CMARA for acoustic risk assessment at low frequencies. Source: own research. (inspired by ISO 14121-2 [28]). The factor of exposure (_Ex_) describes how long an employee is exposed to LFN during work. It has four degrees, and the maximum exposure time is 8 h due to the standard labor shift duration and in compliance with legislation. The input parameters for the proposed method are the action and limit values given by Directive 2003/10/EU [6], the limit values of EU countries, and the hearing threshold curve from ISO 226 [29]. The factor of probability of exposure to LFN with an auditory impact (_Pa_) determines the probability that an employee will be exposed to low-frequency noise to the auditory body at work.