Those five levels remain in effect to this day and serve as the foundation from which NFPA 472 was developed. Anyone who has received training at the Awareness and Operations levels knows that a cornerstone of their training involves learning the uses of the NAERG (North American Emergency Response Guidebook).
Often referred to simply as the ERG, the guidebook is published by the Department of Transportation and provided to emergency response agencies at no cost. The ERG is revised every four years and in recent years has seen the addition of new sections such as pipeline identification and the table of BLEVE capacities. The intent of the ERG has always been to aid in the identification of a hazardous material and provide guidance for the first 15 to 30 minutes of an incident. Such a time frame normally allows for additional resources to arrive and begin taking additional actions.
One drawback of the NAERG has been the necessity that hazardous materials with similar properties have to be grouped together in the guide pages. Under each guide number is a description of the major hazards of the chemicals for that guide page. Descriptions can range from “Mixed Load/Unidentified Cargo” as listed for Guide 111 to “Flammable Liquids – Toxic” for Guide 131. While very useful to see the major hazards for a class of materials in a general sense, tactical decisions involving hazardous materials may depend on a risk assessment of the specific hazards. OSHA 1910.120(q)(6)(ii)(A) requires that personnel trained to the Operations Level have a “Knowledge of the basic hazard and risk assessment techniques.” Hazard and risk assessment requires an “understanding of basic hazardous materials terms” which happens to be a requirement under 1910.120(q)(6)(ii)(C). Specific terms are not listed within OSHA’s subsection, but a good starting point is contained in NFPA 472 and the more recent NFPA 1072. Key chemical and physical terms from NFPA 472 are also found in Safety Data Sheets — referred to as Material Safety Data Sheets before the adoption of the GHS – Globally Harmonized System.
Terms such as flash point, lower explosive limits, vapor density and vapor pressure provide a starting point for the hazard and risk assessment. Flash points and LELs establish the potential fire hazards. Vapor pressure can establish an idea of speed with which a product is off-gassing or evaporating. Vapor density refers to the weight of the product compared to air and whether it will rise or sink. Toxicological terms can range from Immediately Dangerous to Life and Health (IDLH) to Threshold Limiting Value-Time Weighted Average (TLV-TWA - eight hour average exposures) to Threshold Limiting Value-Short Term Exposure Limit (TLV-STEL – 15 minute maximum exposure). These toxicological terms differ, but a simple concept to remember is that the lower the number the greater the hazard. For example, the NIOSH Pocket Guide lists the Time Weighted Average (TWA) of acrylic acid as two parts per million (ppm). The IDLH for phosgene is two ppm. Both chemicals have very low numbers which reflect their extreme toxicity. The difference in the scales is time. IDLH is the critical scale with the effects being “immediately dangerous” to life and health while the TWA reflects a maximum average exposure over an eight hour time span. One could agree that both are extremely toxic with phosgene the greater hazard.
The NIOSH Pocket Guide is helpful in providing many of the key terms listed above. LELs, flash point, signs and symptoms of exposure and incompatibilities are also provided by the NIOSH Pocket Guide. With the information contained in the NIOSH Pocket Guide and a knowledge of the basic hazmat terms and risk assessment techniques an Operations, or Technician, level responder could make additional decisions beyond the initial steps outlined in the NAERG.
A case history I often use to illustrate this involved an overturned tanker with the driver pinned and a corrosive placard with UN 2218. A quick check of the NAERG reveals this product to be acrylic acid.
Readers should also note the letter P beside the Guide No. indicating a chemical that will polymerize. The NAERG refers the user to Guide No. 132.
The NAERG groups chemicals with like hazards together to provide a standard set of recommended actions based on those shared hazards. In the case of acrylic acid, it is characterized as a “Flammable Liquids – Corrosive.” This general heading is accurate for the chemical and at first glance would indicate extreme caution due to the key word flammable. However, if we perform a hazard and risk assessment of the chemical we might determine just how significant is the hazard of flammability. For this we require more data. One source could be shipping papers and Safety Data Sheets. Another source easily accessible via electronic or paper versions is the NIOSH Pocket Guide — so named because earlier editions were small enough to fit in your back pocket. Referring to the print version of the book one can see that the flash point (abbreviated as Fl. P:) is listed as 121 degrees Fahrenheit. It should be noted that it has a very low LEL of 2.4 percent in air.
While 121 degrees F is by DOT definition a flammable liquid, on the date of the case history the weather conditions were cloudy with a temperature of approximately 55 degrees at the time of the incident. The temperature for the duration of the incident never rose above 65 degrees. The product in question was not heated to or above its flash point. Therefore, based on the product and weather conditions at the time of the incident and the additional data from the NIOSH Pocket Guide, the flammability risk could be determined to be minimal. Continuous air monitoring to ensure some unforeseen condition did not change would be appropriate.
With flammability ruled out as a primary hazard for this incident, the next question should be what hazards are posed to the easiest route of exposure — inhalation. The potential hazard from vapors can be assessed by reviewing the product’s vapor pressure (abbreviated as VP: in the NIOSH Pocket Guide). Acrylic acid’s VP is listed as 3mmHg. This abbreviation is expressed as three millimeters of mercury (Hg). For comparison, a chemical’s vapor pressure must be above 760mmHg in order to exist as a vapor. While a chemical with a vapor pressure below 760 is considered a liquid, the higher the vapor pressure the faster the rate of evaporation.
Vapors from acrylic acid, based on its vapor pressure, are a low hazard. However, a low vapor pressure does not necessarily mean the product’s vapors can be overlooked. The NIOSH Pocket Guide provides a single “Exposure Limit” – a NIOSH Recommended Exposure Limit (REL). A NIOSH REL is considered a time weighted average for up to a 10 hour workday within a 40 hour workweek. For acrylic acid the maximum average exposure is limited to two ppm. As described earlier, such a low number indicates a chemical with a high degree of toxicity, but a low vapor pressure indicates the rate of evaporation to be quite slow. Without air monitoring in place to establish concentrations, responders would have to rely on SCBA for respiratory protection if working downwind from any release.
On the day of the accident units on scene immediately requested assistance from the local hazmat team due to an active leak from the tanker. HazMat personnel, using a risk assessment process and NIOSH Pocket Guides, were able to communicate via radio to units on scene that their risk from fire was minimal and that if they could remain out of the product and upwind — or utilize SCBA for respiratory protection — they could affect extrication of the driver. Units on scene were able to rapidly extricate the driver and withdraw from the immediate area of the tractor trailer until the arrival of hazmat resources. Utilizing air monitoring equipment, the hazmat team determined that the airborne concentrations of the product never exceeded two ppm for the duration of the incident for personnel in the warm or cold zones.
As this example shows, a course of action could be determined with additional information and applying the knowledge responders would have garnered from being trained to the operations level. The NIOSH Pocket Guide is an excellent resource, but responders should keep in mind it does not contain all of the potential chemicals that could be encountered nor should it be considered the only source of information in a hazmat emergency