Warning levels

Level Safe membership General membership Dangerous membership Very dangerous membership Extremely dangerous membership Early-warning level... 

Figure 15.1 shows the effect of maintenance and rehabilitation actions to the pavement s level of service and pavement s life. It has been assumed that for a certain period, no maintenance is required for, say, a 20-year design period pavement. Figure 15.1 also shows the warning level and the minimum allowable level, or action, of service set. 

In the United States, the PSI values for new pavements are considered to range from 4.2 to 4.7, depending on the quality of the construction. The PSI value is decreased as pavement is in use, and usually when the PSI value is below 2.0, that is, the pavement is in poor condition and at an unsatisfactory level, immediate rehabilitation should be considered. A PSI value of 2.5 is usually considered as a warning level for future pavement rehabilitation works. 

Category 3 Moderate deterioration - warning level of concern. The deterioration is becoming serious and needs to be investigated. Priorities for more detailed (scheme level) investigations depend on the extent and values of the condition parameters. 

Maximum blood lead levels are usually stipulated above which a worker must be removed from further exposure. These levels are generally in the range of 50 to 70 pg/dL for men and 20 - 40 pg/dL for women. In many places women of childbearing age are not employed where lead exposure can occur. It is also common in the industry to have warning levels and also a requirement that a worker cannot return to the workplace where exposure has occurred until the BLL drops by at least lOpg/dL below the removal limit. Table 15.4 shows BLL removal limits in a wide range of countries. 

The principle of the control chart is to plot the measured values of the control parameter and compare them with a mean, or expected, value and with various control limits. These would be normally set above and below the mean at levels corresponding to 95 % and 99.8 % confidence limits. Assuming that the process or parameter is in control, there is only a one-in-20 chance of a measurement falling outside the 95 % levels, called the warning levels (UWL and LWL in Figure 15.2) and only a one-in-500 chance of it falling outside the 99.8 % action levels (UAL... 

Italian Ministry of the Environment IME 1994. Updating of the technical rules concerning the concentration limits and the precautional and warning levels regarding the atmospheric... 

Control, Signaling, and Levels of Detection. We recommend that two levels of detection be provided, a low warning level set at 1/2 TLV (threshold limit value) and a high alarm level set equal to TLV (code-required). If the high level is reached, an alarm is sent to the ECS, a distinct toxic gas evacuation signal must be broadcast locally throughout the area, and the detected gas supply line must be automatically shut off. 

It is not a great step to go from here with a fully integrated system that controls and monitors the whole plant with safety warnings, level alarms, maintenance prompts and a complete regular costing and audit of the plant performance. 

The chart shows that the system is in control during the first 6 samples analyzed, but the upper warning level has been breached by result 7. However, the next 8 results are within the warning levels, but results 17 to 20 indicate a downward trend culminating with both lower limits being breached indicating a loss of control due to one or more determinate errors. At this point, the causes should be sought and remedial action taken. 

---