Toxic Gas Effects analysis involves the study and assessment of the adverse effects of toxic substances on living organisms, ecosystems, or the environment.
There are several benefits to the assessment of toxic gas effects such as;
- Occupational Health and Safety: This is to ensure the safety of workers. Especially, where employees may be exposed to hazardous gases.
- Emergency Response: Quantifying toxic gases during emergency situations, such as chemical spills, or accidental leaks will help emergency responders take appropriate measures to protect on-site personnel and facilities.
- Health Risk Assessment (HRA): Evaluate the potential health risks associated with exposure to specific toxic gases. This includes assessing the cumulative impact of multiple gases and determining the level of risk for individuals and populations.
Safety Consideration
Many useful measures are available to use as benchmarks for predicting the consequence of whether that exposure will result in injury or death.
- Emergency Response Planning Guideline for Air Contaminants (ERPGs) issued by the American Industrial Hygiene Association (AIHA);
- Immediately Dangerous to Life or Health (IDLH) level established by the National Institute for Occupational Safety and Health (NIOSH);
- Threshold Limit Values (TLVs) established by the American Conference of Governmental Industrial Hygienists (ACGIH) including Short-Term Exposure Limits (STELs), Time-Weight Average (TWA), and Celling (C)
- Permissible Exposure Limits (PELs) issued by the Occupational Safety and Health Administration (OSHA).
| Level | Short Definition |
| ERPG-1 | Max Conc. for 1 hr that causes mild adverse health effects. |
| ERPG-2 | Max Conc. for 1 hr that causes irreversible or serious health effects. |
| ERPG-3 | Max Conc. for 1 hr that causes life-threatening. |
| IDLH | Concentration that causes death or permanent adverse health effects. |
| TLV-STEL | Max Conc. for 15 min exposure without suffering |
| TLV-TWA | Average Conc. for continued exposure (40 hr/wk) without suffering |
| TLV-C | Conc. that should not be exceeded at any time. |
Permissible Exposure Limit (PEL) provides three (3) levels, similar idea with the Threshold Limit Value (TLV), both standards provide TWA, STEL, and Celling value where the PELs are developed by OSHA but the TLV is developed by ACGIH.
Lethal Concentration (LC)
Lethal Concentration (LC) refers to the concentration of a substance at which a specific effect. It is a term commonly used in toxicology to describe the concentration of a substance that is lethal to a given percentage of test organisms.
| LC 1% | The level concentration at which 1% of test organisms die. |
| LC 50% | The level concentration at which 50% of test organisms die. |
| LC 90% | The level concentration at which 90% of test organisms die. |
| LC 99% | The level concentration at which 99% of test organisms die. |
Application
Example design criteria for designing Restricted Area and Impacted Area.
| Equipment | Scenario | Criteria |
| Flare | Un-ignited toxic gas release, cloud dispersion from gas/two-phase or liquid accidentally releases | LC 1% |
| Flare | Emergency operation (ignited) | TLV-TWA |
| Flare | Flame out | LC 1% |
| Cold vent | Emergency operation | TLV-STEL |
| Blow out | Un-ignited release | LC 1% |
| Equipment | Scenario | Criteria |
| Flare | Un-ignited toxic gas release, cloud dispersion from gas/two-phase or liquid accidentally releases | IDLH |
| Flare | Flameout | IDLH |
| Cold Vent | Emergency operation | IDLH |
| Blow out | Un-ignited release | IDLH |
Probability of Fatalities
The most common method to calculate the probability of fatalities can be represented by the probit function since the probit function (logarithm of dose) provides a much straighter line that is close to the typical dose-response curve. Below is the basic equation of the probit function
And below is the conversion table from probit variable to probability or percentage.
The probit functions are available for a variety of exposures, including exposures to toxic materials, heat, pressure, sound, and etc. Below is the probit function to estimate fatalities level for lethal toxicity.
| Substance | a | b | n |
| Ammonia | -35.9 | 1.85 | 2 |
| Benzene | -109.78 | 5.3 | 2 |
| Carbon Monoxide | -37.98 | 3.7 | 1 |
| Chlorine | -8.29 | 0.92 | 2 |
| Sulfur Dioxide | -15.67 | 2.10 | 1 |
PROcess Safety TASK 