Transcripts excerpts DTSC Hearing on 1-19-05 with Guest Debbie Otis, Senior Toxicologist, regarding dangers of methane and hydrogen sulfide chemicals
DR. OTIS: I’m Debbie Otis. I am a Senior Toxicologist from Sacramento, where my group is. We have about six or seven toxicologists that work for me. A number of them have worked on this project in the past. So I want to talk a little bit about what the chemicals are that we’ve found there that we’re really concerned with.
As Jennifer mentioned, during the remedial investigation we looked for hundreds and hundreds of different possible chemicals that could be on the site. From that, we identified 40 chemicals that we found sporadically and at relatively low concentrations. We had two chemicals, however, that we found at higher concentrations and that are of concern in terms of future students and faculty being at the buildings and at the site, and those, again, are methane and hydrogen sulfide. And those were identified as the chemicals that need some kind of mitigation, some additional work to be done in order to provide a protective environment.
As Jennifer mentioned, the problem with methane is that it can either ignite or explode at certain concentrations. Methane in and of itself doesn’t make people sick, so it doesn’t cause cancer, it doesn’t cause birth defects, it doesn’t in any way act like we normally see a toxic chemical to act. But it can explode, so obviously there’s a real health concern here, yes, and something we have to look at. And protect from. The lower explosive limit, which Jennifer mentioned, is 53,000 ppm. Again, the highest concentration we saw was 900,000 up in the baseball field, and that, again, was at 40 feet deep. As we took samples closer and closer to the surface, those concentrations dropped dramatically so that by the time we got to the surface, we were nowhere near this lower explosive limit. Yet this is the standard that we use when we’re looking at whether methane can explode. The regulatory way we approach that, then, is looking at protecting in percentage increments. So for the lower explosive limit, we want to regulate it a fraction of that, and we look at 5%, 10%. Those are generally what regulatory agencies are looking at. Later on, we’ll talk a little bit, because we go much lower than that. Okay? But 5% would be 2500, 10% would be around 5300 parts per million.
Now, hydrogen sulfide was also detected, primarily out in the baseball field. In the area of the buildings itself, we found a couple of trace amounts not actually under where the buildings are, but we did find a few right around there. And methane, too, we only found much smaller concentrations where we were going to actually have the buildings placed. So hydrogen sulfide was elevated out in the baseball field.
Now, hydrogen sulfide’s a different story from methane. Hydrogen sulfide can cause health effects. It is a toxic chemical. At low concentrations – and this is really what we’re looking at, students and faculty potentially being exposed to at the school – it can irritate the lungs, the nose, the eyes; it can cause headaches, nausea; you can smell it, even at these concentrations. And hydrogen sulfide has a very distinctive smell, and you’ve probably smelled it before. It’s a sulfur smell, kind of rotten egg kind of smell, so it’s very distinctive and people do notice it. At high concentrations – and these are concentrations that are usually seen in occupational settings, sewer workers who go down into enclosed spaces can be exposed to very high concentrations. And this can be very serious and the effects can occur in a very short period of time, but it can depress the central nervous system, and then it can interfere with breathing, it can cause convulsions, and ultimately it can actually cause death. And the higher the concentration, the shorter amount of time you can be exposed to it before any of these symptoms or deaths can occur.
So this is to kind of give you some framework for how some of the regulatory agencies have looked at hydrogen sulfide. The OSHA, which is the Occupational Safety and Health Administration – they’re the ones that regulate the workplace, they’ve set a permissible exposure level, that’s the PEL, at 10 ppm. So that’s what they say workers can be exposed to for eight hours a day. Now, California EPA has set values called RELs, and those are Reference Exposure Levels, and that’s the levels they think that the general population would be safe breathing. Generally, OSHA allows higher concentrations, workers to be exposed to higher concentrations that CAL EPA would, than we would a DTSC. So short-term exposure, the REL for short-term exposure is .03 ppm. And for long-term exposure, it’s .008 ppm. So you can see that’s about a thousand fold lower than what the occupational standard is. And we’re using, obviously, not occupational standards here for the proposed high school, but we’re looking at concentrations that CAL EPA has said that are protective for the general population.
So the action levels – and these are for inside the building – and the reason we say it this way is because that’s the space where we’re likely, if there’s a problem, to see the highest concentration. That’s inside of buildings that can accumulate, gasses can accumulate different contaminants like that, and so we’re setting our standards in the place that we’re likely to see the highest concentrations, and that’s within the buildings. And the action level for inside the building is .01 ppm, and that’s slightly rounded up from the long-term REL of .008. And then for methane, it’s 500 ppm, and that’s about 1%. Remember a few minutes ago I talked about the other agencies that look at 5 or 10% of the LEL? Well, what we’re looking at for inside the building here is 500, and that’s 1% of the lower explosive limit.
So with that, I’m going to turn this over to Mike Sorenson, who’s going to talk about the different strategies that are proposed for reaching these goals.
As Jennifer mentioned, during the remedial investigation we looked for hundreds and hundreds of different possible chemicals that could be on the site. From that, we identified 40 chemicals that we found sporadically and at relatively low concentrations. We had two chemicals, however, that we found at higher concentrations and that are of concern in terms of future students and faculty being at the buildings and at the site, and those, again, are methane and hydrogen sulfide. And those were identified as the chemicals that need some kind of mitigation, some additional work to be done in order to provide a protective environment.
As Jennifer mentioned, the problem with methane is that it can either ignite or explode at certain concentrations. Methane in and of itself doesn’t make people sick, so it doesn’t cause cancer, it doesn’t cause birth defects, it doesn’t in any way act like we normally see a toxic chemical to act. But it can explode, so obviously there’s a real health concern here, yes, and something we have to look at. And protect from. The lower explosive limit, which Jennifer mentioned, is 53,000 ppm. Again, the highest concentration we saw was 900,000 up in the baseball field, and that, again, was at 40 feet deep. As we took samples closer and closer to the surface, those concentrations dropped dramatically so that by the time we got to the surface, we were nowhere near this lower explosive limit. Yet this is the standard that we use when we’re looking at whether methane can explode. The regulatory way we approach that, then, is looking at protecting in percentage increments. So for the lower explosive limit, we want to regulate it a fraction of that, and we look at 5%, 10%. Those are generally what regulatory agencies are looking at. Later on, we’ll talk a little bit, because we go much lower than that. Okay? But 5% would be 2500, 10% would be around 5300 parts per million.
Now, hydrogen sulfide was also detected, primarily out in the baseball field. In the area of the buildings itself, we found a couple of trace amounts not actually under where the buildings are, but we did find a few right around there. And methane, too, we only found much smaller concentrations where we were going to actually have the buildings placed. So hydrogen sulfide was elevated out in the baseball field.
Now, hydrogen sulfide’s a different story from methane. Hydrogen sulfide can cause health effects. It is a toxic chemical. At low concentrations – and this is really what we’re looking at, students and faculty potentially being exposed to at the school – it can irritate the lungs, the nose, the eyes; it can cause headaches, nausea; you can smell it, even at these concentrations. And hydrogen sulfide has a very distinctive smell, and you’ve probably smelled it before. It’s a sulfur smell, kind of rotten egg kind of smell, so it’s very distinctive and people do notice it. At high concentrations – and these are concentrations that are usually seen in occupational settings, sewer workers who go down into enclosed spaces can be exposed to very high concentrations. And this can be very serious and the effects can occur in a very short period of time, but it can depress the central nervous system, and then it can interfere with breathing, it can cause convulsions, and ultimately it can actually cause death. And the higher the concentration, the shorter amount of time you can be exposed to it before any of these symptoms or deaths can occur.
So this is to kind of give you some framework for how some of the regulatory agencies have looked at hydrogen sulfide. The OSHA, which is the Occupational Safety and Health Administration – they’re the ones that regulate the workplace, they’ve set a permissible exposure level, that’s the PEL, at 10 ppm. So that’s what they say workers can be exposed to for eight hours a day. Now, California EPA has set values called RELs, and those are Reference Exposure Levels, and that’s the levels they think that the general population would be safe breathing. Generally, OSHA allows higher concentrations, workers to be exposed to higher concentrations that CAL EPA would, than we would a DTSC. So short-term exposure, the REL for short-term exposure is .03 ppm. And for long-term exposure, it’s .008 ppm. So you can see that’s about a thousand fold lower than what the occupational standard is. And we’re using, obviously, not occupational standards here for the proposed high school, but we’re looking at concentrations that CAL EPA has said that are protective for the general population.
So the action levels – and these are for inside the building – and the reason we say it this way is because that’s the space where we’re likely, if there’s a problem, to see the highest concentration. That’s inside of buildings that can accumulate, gasses can accumulate different contaminants like that, and so we’re setting our standards in the place that we’re likely to see the highest concentrations, and that’s within the buildings. And the action level for inside the building is .01 ppm, and that’s slightly rounded up from the long-term REL of .008. And then for methane, it’s 500 ppm, and that’s about 1%. Remember a few minutes ago I talked about the other agencies that look at 5 or 10% of the LEL? Well, what we’re looking at for inside the building here is 500, and that’s 1% of the lower explosive limit.
So with that, I’m going to turn this over to Mike Sorenson, who’s going to talk about the different strategies that are proposed for reaching these goals.
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