Protecting both people and the environment whilst meeting the operational needs of business is an important role and a key requirement of the Code of Federal Regulations (CFR) in the U.S. Similar legislation exists worldwide with a focus on hazard identification, risk assessment and the provision of appropriate control measures, as well as health surveillance in some cases.
Whilst toxic gases such as hydrogen sulphide and carbon monoxide are a major concern because they pose an immediate danger to life, long-term exposure to relatively low-level concentrations of other gases or vapors such as volatile organic compounds (VOCs) are of equal importance because of the chronic illness that can result from that ongoing exposure.
Some VOCs are hydrocarbons, but not all hydrocarbons are VOCs. The latter have a significant vapor pressure at normal ambient temperature, which means they evaporate or volatilize at low temperatures so they easily enter the body through normal breathing.
Benzene exposure
Benzene evaporates easily and most people can just detect its distinctive smell at concentrations between 2.4 and 5 parts per million (ppm) in air.
As well as inhalation, benzene can be absorbed into the body through the skin or by swallowing material containing it. The effect on workers' health depends on how much benzene they are exposed to and for how long. As with other organic solvents, the immediate effects of a single exposure to a high concentration (hundreds of ppm) include headache, tiredness, nausea, dizziness and even unconsciousness if the exposure is very high.
In May 2014, the U.S. Environmental Protection Agency (EPA) estimated some 5 million Americans, not counting those with workplace exposures, face heightened cancer risks from benzene and 68 other carcinogens released into the air by the nation's 149 oil refineries. This is greater than a one-in-1- million lifetime cancer risk.
In June 2014, California officials lowered the long-term exposure level to benzene, and the state is also considering classifying benzene as not just a human carcinogen but also a "toxic air contaminant which may disproportionately impact children."
Making it clear cancer and the other health risks posed by petroleum refineries on nearby communities are unacceptable, the monitoring and control of benzene concentration levels around the perimeter of all U.S. oil refineries has been proposed by the EPA under the "Residual Risk Program."
The proposed rule would revise emission control requirements for flares, storage tanks and coking units at petroleum refineries and require monitoring around refineries to ensure neighboring communities are not being exposed to hazardous air pollution. This proposal would also set maximum achievable control technology standards for delayed coking units, which the EPA described as a "significant" unregulated source of hazardous pollutant emissions at refineries.
The EPA said it anticipates the proposal will have a "minimal" economic effect on the refining industry but could reduce emissions of hazardous air pollutants such as benzene and xylene by an estimated 5,600 tons per year.
From a long-term (chronic) health perspective, the World Health Organization (WHO) and International Agency for Research on Cancer (IARC) classify benzene as a Group 1 carcinogen. Prolonged exposure to high concentrations of benzene causes leukaemia and impacts red and white blood cells. The WHO has not set a standard for ambient benzene concentrations, stating there is no safe level of exposure, but many countries use an annual average standard of 3.6g m-3, which is equivalent to 1 part per billion (ppb) or 0.001 ppm.
Benzene detection
It is advisable to use an appropriate form of quantitative monitoring, with the onus on the employer to do the monitoring. There are methods published by the National Institute for Occupational Safety and Health (NIOSH) in the U.S. that can be used to capture air samples for later analysis, but by definition this occurs after exposure might have taken place. As a result, real-time methods are preferable, which can range from fixed, permanent systems for fenceline applications to hand-held devices for area measurements or confined space entry and personal monitors that can alert a worker of an immediate risk.
What is a photoionization detector?
Known as photoionization detectors (PIDs), these instruments incorporate a UV lamp that generates high-energy photons that pass through the lamp window and a mesh electrode into the sensor chamber. Sample gas is pumped over the sensor, and about 1 percent of it diffuses through a porous membrane filter into the other side of the sensor chamber. When a photon with enough energy strikes a molecule (M) , an electron (e-) is ejected. The M+ ion travels to the cathode and the electron travels to the anode, resulting in a current proportional to the gas concentration. The electrical current is amplified and displayed as a ppm or ppb concentration.
For more information, visit www. ionscience.com or call (877) 864-7710.
