Over the years, we have witnessed significant improvements in worker protection. One area that has not kept pace is that of portable air filter equipment, intended to provide Grade D breathing air that is attached to non-breathing air compressors. Fortunately, next-generation products are becoming available that have many new features to improve the safety for users of Grade D breathing air equipment.
The OSHA Respirator Protective Equipment Standard (1910.134) requires “the employer to provide employees using atmosphere-supplying respirators (supplied-air and SCBA) with breathing gases of “high purity” and further states that “compressed breathing air shall meet at least the requirements for Grade D breathing air described in ANSI/Compressed Gas Association Commodity Specification for Air, G-7.1.”
Grade D breathing air is required to meet the following standards:
- Oxygen content (v/v) of 19.5-23.5%
- Hydrocarbon (condensed) content of 5mg per cubic meter (mg/m3) of air or less
- CO content of 10 parts per million (ppm) or less
- CO2 content of 1,000ppm or less
- Lack of noticeable odor
- A dew point of at least 10°F below the ambient temperature (i.e., Delta Dew Point of +10°F)
The primary health concern of OSHA standard 1910.134 is carbon monoxide. Carbon monoxide is odorless gas and has serious health effects at low concentrations. It is the most dangerous gas likely to be encountered in a compressed air stream. CO concentrations greater than 10ppm can cause headaches, dizziness and nausea; higher concentrations can be fatal. Therefore, it is critical to be able to detect the presence of CO at low ppm levels, in order to take immediate action to mitigate and reduce operator exposure.
European countries follow the EN 12021-:2014 standard. While similar to the U.S. standard, EN 12021-:2014 imposes more stringent limits for CO (i.e., 5ppm), CO2 (500ppm) and water vapor (25mg/m3).
Using a non-breathing air compressor creates more risk to the operator. Location of the compressor inlet is crucial. It is critically important to have the air inlet in an area that is free of vehicle exhaust and other potential sources of chemical vapors.
Carbon monoxide can be introduced into the compressor not only by direct ingestion of contaminated air, but also by the partial oxidation of organic molecules (e.g., oils) on hot surfaces inside the compressor machinery. There are no cost-effective methods for scrubbing carbon monoxide from breathing air. That is why continuous monitoring is essential.
Breathing air compressors use absorbers and filters to prevent particulates, water and oil vapor contamination from entering the compressed breathing air stream. These filter elements require regular maintenance. If they fail, they can release particulates, water, odor and oil contaminants into the air stream.
Present-day, Grade D breathing air equipment rarely provides anything more than carbon monoxide monitoring. Being able to offer new features, such as dew point measurement and CFM (airflow measurement), improves the safe use of the Grade D Breathing air equipment.
A key question when using any piece of equipment is: What should one expect? Is it working to specification? What was that date of calibration? It is essential to communicate this information. Knowing the date of the last calibration and the time remaining until the next calibration keeps the unit in compliance with the safety plan. Providing this information as the first step of the process and requiring the operator to acknowledge this data improves operator engagement and safety.
The most dangerous threat from the compressor gas stream is carbon monoxide, and the operator using a breathing air system should have simple direct access to this data. Being able to easily view the real-time ppm CO level on the outside of the enclosure is an important function of a Grade D air filtration system.
Simply providing an external alarm light and horn doesn’t allow the operator to confirm the quality of the air supply. Products that lack an external display make it more difficult to observe an exposure trend that could be easily addressed—before the situation becomes dangerous and reaches the alarm level.
A solution to this gap is ENMET’s AirGuard, which uses a large, externally mounted 7in color graphic display that communicates the status of the air stream. It also has two-step alarm settings: one a warning (caution) alarm and a threshold concentration alarm. This display, in combination with a horn and the two alarm setpoint warnings, provide the operator with improved visual and audible information, thus enhancing his/her safety.
Knowing the water contamination level (or dew point) in the air stream is also valuable data for the operator. If the air stream is too dry or wet, it will affect worker productivity. High levels of water in the air stream can cause fogging on the lens of the respirator mask and a corresponding reduction in visibility. This often requires leaving the work area, so that the mask lens can be cleaned and dried.
High moisture levels in the breathing air hose can also foster the growth of highly undesirable mold. An air guard-type of device can address the water contamination problem by including a differential dew point sensor that reports the dryness of the air using a highly visible display with the real-time CO concentrations.
Differential dew point is simply the difference between the temperature of the breathing air (°F) and the dew point (°F) of the breathing air. Class D breathing air requires a minimum differential dew point of +10°F. High differential readings report a dry gas stream, and low readings indicate wet air stream. Therefore, if the differential dew point readings are below 10°F, then adding an additional gas dryer to the airflow would reduce the high humidity level and eliminate the wet air stream, condensing inside of the operator’s protective mask.
One other important performance gap is the ability for a Grade D breathing air instrument to measure the CFM to the mask, in addition to a pressure setpoint value and a theoretical flow value. Being able to know the CFM value real-time with electronic low-flow alarms provides the operator with an additional layer of safety, should a line become physically blocked or obstructed.
Additionally, should the compressor not be able to keep up its system outlet pressure due to increased air demand by users, the inlet pressure will decline and result in a lower CFM to the mask. These are unsafe conditions that are generally oblivious to the operator, because often these changes are not readily observable. Having CFM caution and alarm setpoints provide a means to alert the operator to reduced or no flow and allows them to seek corrective action. This is one more additional level of protection.
One of the most critical aspects of operating any life safety equipment is a record of performance. Is it safe? Does it have a real-time history of exposures? Can you prove it was working to specification? To help with these questions, the AirGuard has an automatic data log feature that collects data when operated, providing real-time CO values and diagnostic performance data. It also provides a time-date record of calibration that is automatic and unique to the instrument, allowing a convenient record for safety compliance audits.
Today, there is no excuse for remaining in the past. There are next-generation solutions for Grade D breathing air that offer real-time CFM Measurement, Differential Dew Point and a computer-controlled environment to improve worker and workplace safety. IHW