1. Hydrogen Sulfide Hazard Assessment
Introduction:
Why discuss hydrogen sulfide hazards at this time?
- Several mines experiencing H2S issues currently
- Demand for energy driving higher production rates
- H2S emissions highly variable and can lead to unanticipated exposures
- Rapid onset of hazard requires miners to be aware of risks and emergency actions
Presentation will take about 15 minutes but if further general information is desired, phone me. If you have an emergency, get immediate medical assistance.
Erik Vermulen
MSHA, District 9
Coal Safety and Health
District 9 Coal Health

2. Hydrogen Sulfide Hazard Assessment
Introduction
Occurrence in Mines, Scenarios
Detection
Range of Health Effects
Emergency Actions
Action Levels
Hazard and Risk
As with any toxic material, it’s the dose that makes the difference. Factors such as the characteristics of the material, how long you’re exposed, how the concentration varies over time, how much material is deposited in your body, any pre-existing medical conditions, your individual susceptibility, any concurrent exposures to materials impacting the same target organ all impact an individuals response.
During the presentation we’ll discuss the situations that may lead to the rapid on-set of exposures. How H2S is detected will be addressed. The range in responses to various exposure levels will be discussed, along with emergency actions. Various limits apply to different situations to guide individuals in assessing their specific risk.
District 9 Coal Health

3. Hydrogen Sulfide Hazard Assessment
Occurrence in Mines, Scenarios
Generated from reduced biomass (coal, natural gas, garbage), Geochemical sources in sediments, human metabolism
Released from pockets in coal, natural gas vents, supersaturated water
May be wide spread or localized; constant or in pockets of varying concentration
H2S is introduced by both man-made and natural processes.
In the absence of oxygen, geological and biological activity will convert sulfur containing compounds to hydrogen sulfide. The geological processes that formed coal and petroleum also form H2S.
Animal (and human) metabolism forms H2S from some amino-acids, bacteria in the gut and mouth generate H2S, the brain and smooth muscles produce the material through the action of enzymes. The body detoxifies and expels H2S.
Ground water will extract H2S from minerals. When it surfaces in a mine, it can release the gas with any minor disruption.
Vents of natural gas can carry unexpectedly high levels of H2S into a mine.
Pockets of H2S within the coal matrix can vary in volume and concentration.
Bottom line – you can’t predict the amount of H2S you may experience.
District 9 Coal Health

4. Hydrogen Sulfide Hazard Assessment
Detection
Odor: <0.02 ppm – none, 0.13 ppm – perceptible, 1.0 ppm - faint, 5 ppm - moderate, 25 ppm – strong, 100 ppm – lose odor in 2-15 minutes
Electro chemical sensors: calibrated and within shelf-life
Detector tubes and Impregnated Paper: Within shelf-life
Absorb air samples with analytical determination
Biological exposure methods for expired air and tissues
When you first encounter H2S, you can smell it at relatively low concentrations. Unfortunately over time, especially at higher concentrations, your sense of smell fatigues and the odor is no longer detectable. You can’t trust your nose in an emergency situation.
Fortunately, electrochemical sensors and alarms are available for detecting rapid changes in concentration. If calibrated and used in accordance with the manufacturer’s recommendations, they will yield accurate results. The devices can be damaged and a daily “bump test” must be performed to assure they are working. Over time the sensor will fail and when it can no longer be calibrated, they need to be replaced.
Detector tubes and impregnated test papers are still valid indicators of concentration but require approximately 10 minutes of sampling time. They are not useful for full shift or instantaneous level measurements.
Very precise methods are available for tissue and environmental samples but the samples rapidly degrade with time and must be analyzed immediately.
District 9 Coal Health

5. Hydrogen Sulfide Hazard Assessment
Range of Health Effects
(Concentration – Time Effects)
Death due to respiratory failure with brief exposures to very high concentrations (seconds at >1000 ppm)
Acute intoxication with neurological, respiratory, ocular and cardiac symptoms with potential recovery (exposures from minutes to hours at 250 to 1000 ppm, in animals LC-50 ranges from 335 to 587 ppm)
Sub-Acute and Chronic toxicity include: cardiac arrhythmia, neuropathology, respiratory lesions/edema, blood-enzymes, ocular, cellular effects (exposures from 10 – 200 ppm for hours to months)
Lifetime exposures – Carcinogenic, developmental - none
There is substantial uncertainty in the response of human to H2S exposures:
- in a 10 year period 29 fatalities were recorded
- accurate information on the exact duration or level is missing
- extrapolation from animal toxicity data to humans is particularly difficult for H2S
What we do know:
High levels can cause rapid death. Studies report death in 2-3 breaths at 1000 ppm, 5 minutes at 800 ppm, 30 minutes at 600 ppm due to respiratory paralysis. The LC-50 for rodents is reported between 335 and 587 ppm.
Non-lethal exposures may lead to pulmonary edema, neurological damage, cardiac damage, and visual impacts, all which may be related to anoxia.
Lower dose symptoms may include sudden fatigue, headache, dizziness, anxiety, cognitive impairment, loss of verbal fluency and respiratory irritation.
The difference in levels of H2S in brain tissue between normal and acute toxicity may be as small as a factor of two.
District 9 Coal Health

6. Enforcement Surveys for H2S
Chapter 4, Health Inspection Procedures Handbook
Pre-inspection Actions – Select method, pre-calibration, UMF
Walk-Through to document process, duration, frequency, sketch
Select maximally exposed occupation (if refuses can sample BZ)
Follow normal 8-hour, portal to portal sampling
Use Vent Plan method if one is designated, record rationale
With instruments, check periodically, follow/note Manuf. instructions
Place instrument on shirt near breathing zone, note location
Recommend using a second detection method (stain tube, Zefluor tube, OSHA ID141) to verify, record sample time
Record miner’s locations, general duties, variance from normal
Fill out MSHA (MSHA if analysis needed)
District 9 Coal Health

7. Enforcement Surveys for H2S – Cont.
Out-brief miners/operators and notify that a citation may be issued if later data analysis indicates an over-exposure
If instrument TLV-TWA, 8Hr, exceeds 5 PPM notify operator that corrective action may be required – no citation issued but Vent Plan change.
Post Inspection Actions
Post calibrate instrument or bump test
Download data using manufacturer’s software, save files
Evaluated “STEL” file to see if any 15 minute increment > 20PPM
Evaluate TLV file to see if 8 hour >10 PPM
Contact District for assistance in writing the Citation, if applicable
(Note: Instruments not listed by NIOSH or OSHA as standard method – rationale important)
District 9 Coal Health

8. Hydrogen Sulfide Hazard Assessment
Range of Health Effects
(Receptor Susceptibility)
Health status and pre-existing pathology
asthmatics, heart patients
Concurrent exposures to organs (dust, CO, low 02)
Limited human data and uncertainty in applying animal data to human response
Small exposure range from no-effect to acute toxicity with uncertainty in epidemiological exposure levels
As indicated the primary physiological effect appears to be respiratory distress with physical damage consistent with anoxia.
Studies assessing individuals with pre-existing cardiopulmonary disease suggests they may be more sensitive than the normal healthy worker. One study indicated the beginnings of acute pulmonary effects in asthmatics at 2 ppm.
No studies were identified that specifically looked at subjects who work with dusty atmospheres or at low oxygen levels. The acute toxicity suggests there may be additive effects for sub-acute symptoms.
Individual sensitivity in both humans and animal subjects seems to vary. New toxicological data coming available has led scientists to lower their estimates of safe levels for both working lifetimes and emergency situations.
District 9 Coal Health

9. Hydrogen Sulfide Hazard Assessment
Emergency Actions
Explosive – 4.3 to 46%, Heavier than air: evacuate and remove ignition sources, ventilate, water spray
Respiratory Hazard – Use approved SCBA to rescue victims, if breathing apply 02, if not apply CPR, seek medical attention immediately, keep warm and calm, test atmosphere for toxic concentrations
Eye Irritant – irrigate eyes with water if irritated
Many of the emergencies related to H2S have occurred in confined space areas with poor ventilation.
The gas is heavier than air and will sink to the floor if not in turbulent air flow. If it accumulates in low areas, it is susceptible to reach explosive limits. Emergency actions for fire fighting include removing ignition sources, using water spray to cool and remove H2S.
Rescue teams have been overcome by H2S when entering confined spaces. Approved self-contained breathing (SCBA) equipment is recommended for rescue. If victims are breathing, oxygen support has been indicated. If not, use CPR to revive the victim. Treat for shock and get medical attention.
District 9 Coal Health

10. Hydrogen Sulfide Hazard Assessment
Consensus Levels
MSHA: TLV – 10 ppm, Ventilation plan actions
20 ppm for 15 minutes, allowable excursion
OSHA: 20 ppm (C), min. peak / 1/shift
ACGIH: 10 ppm TLV-TWA, 15 STEL (NIC 1/5 ppm)
NIOSH: IDLH 100 ppm (Imminent Danger)
AIHA: ERPG3 100 ppm (60 min.) (life threatening)
ERPG2 30 ppm (60 min.) (serious / irreversible)
Numerous consensus levels have been developed for various situations. One trend is apparent and that is a general lowering of levels that are considered safe. In coal mining, the ventilation plans may contain criteria and control methods specific to a mine.
When many of the studies supporting these levels were conducted, there were limited analytical techniques for exposure durations less than minutes. Not many studies were performed on brief, peak exposures. Analysts agree that exposures to 100 ppm for a half-hour are life threatening.
Very brief exposures (seconds) to levels less than 100 ppm are less well understood. What is clear is that brief exposures above the TLV-TWA can be cited. The margin of safety between the IDLH and on-set of fatalities is very small.
District 9 Coal Health

11. Hydrogen Sulfide Hazard Assessment
Summary
Acute Risk: Moderate to high – respiratory failure, cardiac and neurological damage, ocular irritation
Small range of significant effects – many will tolerate 50 ppm; some fatalities, many injuries at 500 ppm
Odor not dependable to detect; use meters, detectors
Use air supplied respirators for rescue; Provide O2 / CPR
Explosive, may collect in low areas
Exposure concentrations may change without warning when low ventilation rates exist
Stay out – Stay alive
In summary, the acute risks are real. The margin of safety between levels that can easily exist and levels that result in fatalities is small.
Our ability to detect H2S by odor is not dependable but meters and detectors if calibrated and not damaged give us reliable information.
Control of exposure levels is very difficult due to unanticipated releases. These releases could put us into hazardous situations very rapidly. This is particularly true in low areas with poor ventilation.
Rescue teams must be particularly aware of hazards and use approved self contained respiratory protection.
Any questions?
District 9 Coal Health