Breathing Comfort Evaluation of Compressed Air Self-Rescue Devices: Parameters, Methods and Standard

Breathing comfort evaluation of compressed air self-rescue devices verifies that the emergency air delivered to miners through underground compressed-air pipelines is clean, stable, and physiologically comfortable during prolonged entrapment. This technical article explains the evaluation scope, sample requirements, key testing items such as airflow, breathing resistance, temperature, humidity, noise and air quality, laboratory methods, and applicable international and national standards for accredited third-party testing.

Technical Overview

A compressed air self-rescue device is a fixed emergency breathing system installed in underground coal mines and tunnels. It typically consists of a mine compressed-air pipeline, a pressure-reducing station, filters, branch lines, quick-connect couplings, breathing hoses, and half masks, full masks, or hoods arranged at self-rescue points near working faces, along escape routes, and at refuge chambers. When ambient air becomes oxygen-deficient or contaminated by toxic gases during a fire, explosion, gas outburst, or abnormal emission, miners connect to the device and breathe filtered, regulated compressed air while awaiting rescue or organizing evacuation.

Breathing comfort evaluation is the systematic assessment of whether the delivered air is not only safe but also physiologically and subjectively acceptable to the user. Even when oxygen content and contaminant levels meet safety limits, poor comfort factors—excessively cold or dry air, high flow noise, elevated breathing resistance, heat and carbon dioxide buildup inside a hood, or an ill-fitting facepiece—can cause panic, discomfort, and premature removal of protection. Comfort performance therefore directly affects user tolerance, decision-making ability, and survival time in an emergency.

The evaluation is typically performed by accredited third-party laboratories against recognized frameworks, including EN 14594 for constant-flow compressed-air line breathing apparatus, EN 14593-1 for demand-valve apparatus, EN 12021 for breathing air quality, the ISO 16900 series for respiratory protective device test methods, and relevant GB and coal-industry MT standards, together with the minimum per-person supply requirement of approximately 0.1 m³/min stipulated in mine safety regulations.

Testing Samples

Samples submitted to accredited third-party laboratories should represent the final production configuration, including all components that contact the airway or influence the delivered air. Test units are conditioned in a standard laboratory atmosphere before evaluation, and both new and artificially aged samples may be included to assess comfort retention over service life.

Complete Self-Rescue Units

Cabinet-type, wall-mounted, or pipeline-mounted assemblies comprising the pressure reducer, filter element, shut-off valve, pressure gauge, distribution manifold, breathing hose, and mask or hood. A minimum of three complete units is generally recommended so that multi-user draw-down behavior can be verified at stations designed for three to six simultaneous users.

Components and Consumables

Pressure-reducing valves, air filter cartridges, breathing hoses, half masks, full face masks, protective hoods, mouthpiece-and-noseclip assemblies, quick couplings, and head harnesses, submitted in sufficient quantity for destructive or repeated-cycle testing.

Pipeline Supply Points and Breathing Air

For installed mine systems, representative terminal outlets are sampled on site so that delivered air quality, pressure, and flow can be characterized under real pipeline conditions rather than laboratory bench conditions alone.

Aged and Environmentally Conditioned Samples

Samples subjected to temperature cycling, humidity exposure, dust loading, and storage aging, used to confirm that comfort parameters such as breathing resistance and noise do not degrade below acceptable thresholds during the declared service life.

Testing Items

Breathing comfort evaluation combines objective physiological parameters with subjective human-factor assessments. The core testing items include:

• Supply airflow rate per user, with typical acceptance at or above 100 L/min (0.1 m³/min) per person at the rated inlet pressure range
• Static and dynamic air pressure at the breathing interface, including regulator stability under fluctuating pipeline pressure and multi-user demand
• Inhalation and exhalation breathing resistance measured at standard and high ventilation rates
• Delivered air temperature at the mouth or hood inlet across the pipeline operating range
• Relative humidity and dew point of the delivered air, to identify excessively dry conditions that cause throat and airway irritation
• Acoustic noise at the ear position, since regulator and flow hiss affects tolerance and speech intelligibility
• Inhaled carbon dioxide concentration inside the mask or hood dead space under simulated breathing
• Oxygen content of the delivered air, typically within 19.5% to 23.5% by volume
• Contaminant limits in accordance with EN 12021, including carbon monoxide (commonly ≤ 5 ppm), carbon dioxide (commonly ≤ 500 ppm), oil mist (commonly ≤ 0.5 mg/m³), particulate matter, and water content
• Odor evaluation of the delivered air, with no noticeable odor permitted
• Pressure-relief and over-pressure protection performance of the reducing station
• Practical performance and subjective comfort scores, covering facepiece fit, strap pressure, visibility, speech communication, thermal sensation, and perceived breathing effort
• Continuous supply duration at rated load and consistency of all comfort parameters over the test period

Testing Methods

Testing is performed on a purpose-built bench supplied with conditioned compressed air, together with a breathing simulator, precision flow and pressure instrumentation, and climatic control, following the general principles of the ISO 16900 series and the apparatus-specific requirements of EN 14594 and EN 14593-1.

Airflow and Pressure Measurement

Delivered flow is measured with thermal mass flow meters or calibrated rotameters at the mask inlet across the full declared inlet pressure range. Multi-user draw-down tests connect three to six breathing circuits simultaneously to confirm that per-person flow remains above the minimum requirement and that manifold pressure remains stable when pipeline pressure fluctuates.

Breathing Resistance Testing

A mechanical breathing machine generates sinusoidal ventilation at reference minute volumes of approximately 40 L/min for light workload and up to 100–120 L/min for heavy workload, with peak inspiratory flows up to 160 L/min. Differential pressure transducers record inhalation and exhalation resistance across the facepiece; acceptance thresholds are typically expressed in millibars depending on the applicable standard and the flow rate applied.

Microclimate Assessment

Fine-wire thermocouples at the mouth region and miniature humidity probes measure the temperature and relative humidity of the delivered air. Tests are repeated across pipeline inlet temperatures from approximately 0 °C to 40 °C to identify cold-air complaints in deep shafts and heat accumulation near compressors; comfortable delivered-air temperature at the breathing interface is generally expected to fall roughly between 16 °C and 32 °C, with relative humidity high enough to avoid drying of the airway.

Noise Measurement

A-weighted sound pressure is measured with a class 1 sound level meter at the simulated ear position during steady flow and simulated breathing cycles. Common acceptance limits keep noise below 85 dB(A), with best-practice targets below 70–75 dB(A) so that shouted warnings and radio communication remain intelligible.

Carbon Dioxide Accumulation and Air Quality Analysis

The breathing simulator injects carbon dioxide at a rate equivalent to human exhalation while non-dispersive infrared analyzers measure mean inhaled CO₂, which is typically limited to about 1.0% by volume. Delivered air quality is verified using electrochemical or chromatographic analysis for CO and CO₂, paramagnetic or zirconia sensors for O₂, gravimetric or infrared methods for oil mist, and a trained odor panel in accordance with EN 12021.

Practical Performance and Subjective Comfort Scoring

Human subject trials following practical performance principles similar to those of the ISO 16900 series require test subjects to perform standardized walking and head-movement tasks while connected to the device. Structured questionnaires using Likert scales rate breathing effort, thermal comfort, dryness, noise annoyance, facepiece pressure, and overall acceptability, providing a quantified comfort index that is reported alongside the objective measurements.

Applications

Breathing comfort evaluation results serve multiple stakeholders throughout the product and operational lifecycle:

• Type testing and design validation by manufacturers developing low-noise regulators, humidification stages, wide-view hoods, and ergonomic harnesses
• Procurement acceptance testing by mining groups comparing candidate devices before bulk installation
• Periodic in-service verification of installed systems, including annual or post-overhaul checks of flow, air quality, and component condition
• Commissioning of permanent self-rescue stations and refuge chamber air supply points
• Accident investigation and forensic analysis where device comfort or air quality performance is questioned
• Research and benchmarking for new materials, silencing elements, and flow-optimization designs
• Training programs that demonstrate realistic wearing comfort to build miner confidence in the equipment

FAQ

What is the minimum airflow a compressed air self-rescue device must provide?

Most coal mine safety regulations require a supply of at least 0.1 m³/min (100 L/min) of breathable compressed air per person at the station. Comfort evaluations often test well above this minimum to confirm adequate purging of the facepiece and acceptable carbon dioxide levels during sustained use.

Why is noise included in a comfort evaluation?

High-velocity air passing through regulators and couplings can generate loud hissing that fatigues users and masks warning shouts or radio messages. Keeping noise below approximately 85 dB(A), and ideally below 70–75 dB(A), is essential for communication and long-term tolerance.

How is subjective breathing comfort quantified?

Human subject panel tests combine standardized activity protocols with structured questionnaires that convert thermal sensation, breathing effort, dryness, and overall acceptability into numerical scores. These subjective indices are reported together with objective bench data to give a complete comfort profile.

What standards govern this evaluation?

Commonly applied references include EN 14594 for constant-flow compressed-air line apparatus, EN 14593-1 for demand-valve apparatus, EN 12021 for breathing air quality, the ISO 16900 series for respiratory device test methods, and relevant GB and coal-industry MT specifications, supplemented by mine safety regulations on minimum per-person supply.

Can testing be performed on an installed mine system?

Portable instruments can verify terminal outlet flow, pressure, temperature, and air quality on site. Full breathing comfort evaluation, including simulated breathing resistance, CO₂ accumulation, and practical performance trials, is conducted at accredited third-party laboratories under controlled conditions.

How often should breathing comfort be re-evaluated?

Full comfort evaluation is normally performed at type approval and after any design or material change. Installed systems should undergo periodic functional verification, typically at least annually and after major overhauls, filter replacement cycles, or compressor and pipeline modifications.