In hazardous environments, where atmospheric conditions can be caustic, it’s common knowledge that proper respiratory protection equipment (RPE) is crucial. Indeed, if engineering or operational controls are incapable of reducing or altogether eliminating the airborne hazards that are present, RPE is absolutely required. For example, in a common oil field containing sour gas, it is the right self-contained breathing apparatus (SCBA) that allows operators to conduct and carry out confined-space entry and work, hazardous material handling, hot work, grinding and more.
Protective factor criteria
Companies that develop breathing protection apparatuses for individual use must test and certify their products according to the regional or national health and safety guidelines and standards (regarding use within environments contaminated by particles or gases).
The oil and gas industry employs two international protective factor systems: the Nominal Protection Factor (NPF) and the Assigned Protection Factor (APF). These factors are theoretical protection values based on laboratory-measured performance. However, because they were developed in laboratory tests using a small sample size of trained individuals, the factors may not best represent the true protection factor provided for an individual or operator in the workplace.
In hazardous environments, proper respiratory protection equipment is crucial.
The Simulated Workplace Protection
Factors (SWPFs) refer to the amount of breathing protection that can be achieved realistically by 95 percent of well-trained and supervised personnel. SWPF values are more realistic than NPF/APF values since they were obtained through simulated workplace testing. If available, these values should be used (or are required to be used) when selecting respirators.
Positive versus negative pressure
Positive pressure maintains a small air pressure in the operator’s facemask (via breathing valve/cylinder combination) that is greater than the surrounding atmospheric air pressure. This air flow prevents seal leakage, in a sense, because even if there’s a slight gap in the facemask’s seal (facial hair, facial scars, folded seal, etc.), there is a flow of clean air out of the device, preventing the outside air from coming in. For many hazardous applications, a positive-pressure SCBA is preferable.
Negative-pressure SCBAs do not have an air cylinder or a breathing valve, but would typically have a filter canister. Air is delivered to the wearer when they simply breathe. The pressure inside the mask is reduced to less than that of the pressure outside the mask — thus, “negative pressure.” The risks are greater with negative pressure compared to positive pressure because any break in the facemask’s seal could compromise the wearer’s safety.
Current test procedures
The responsible international or national Occupational Safety and Health (OSH) organizations use different test methods to classify and certify respiratory protection equipment of the category Personal Protective Equipment (PPE) by their protective factors.
Most test methods use simulated pollutants. Measured in each case are the outer atmospheric concentration and the concentration of the pollutant in the breathing valve of a respirator. The simulated pollutant can be both gaseous and particulate.
Other test methods relate to job-specific environmental conditions. They are called Workplace Protection Factor Tests (WPFs). In these tests, the measuring takes place during the actual activity under the influence of true ambient pollutants.
Tests with particles
Such methods are only suitable for testing the protection of respirators for particles. Since gases behave differently than particles, this approach allows no conclusion about protection against hazardous gaseous pollutants.
TIL test
For the Total Inward Leakage (TIL) test, according to EN 136 (full face mask) and EN 137 (SCBA units), more than one person applies the test respirators as part of a certification exam. The subjects are locked in a chamber, which is then flooded with the simulation gas sulfur hexafluoride (SF6) in a defined concentration and distribution.
The measurement results describe the ratio of pollutant outside and inside the respirator. Other than the method mentioned above, the results for the TIL test are valid for both particle- and gas-loaded atmospheres. Masks and respirators that meet the minimum requirements may be used in both pollutant areas. The minimum requirement for the leakage value (TIL) of these device classes as defined by the standard is less than .05 percent.
A respirator mask according to EN 136 has a TIL of less than or equal to .05 percent and ensures an NPF of 2,000.
If this respirator is used (e.g., with a breathing apparatus that generates a positive pressure) in the mask, the leakage value can be significantly higher. The breathing apparatus may then achieve a protection factor of up to 10,000 or more.
How to assess testing procedures
SWPF and WPF tests provide information on the sealing seat of respiratory protective devices while in use. The WPF test measures under real conditions with real pollutants. It is important to choose a method that is as significant and realistic as possible; however, an ethical question arises: Is it acceptable to expose a subject to this potentially harmful or deadly environment? SWPF tests are only an authoritative forecast, being a simulation of typical workplace conditions (e.g., by the use of gaseous or particulate pollutants).
Summary
When selecting the most suitable respirator, one must consider the maximum allowed — and anticipated — contaminations at the specific workplace. Therefore, Dräger tests their breathing equipment through an independent certifying authority. Yes, there is product testing against the appropriate international standards — NIOSH, OSHA, etc., where applicable — but, unlike most manufacturers, Dräger seeks out independent certification beyond that which is internationally required.
For more information, visit www. draeger.com or call (800) 858-1737.
