# Permissible exposure limit

The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agent such as high level noise. Permissible exposure limits were established by the Occupational Safety and Health Administration (OSHA). Most of OSHA's PELs were issued shortly after adoption of the Occupational Safety and Health (OSH) Act in 1970.
Chemical regulation is sometimes expressed in parts per million (ppm), but often in milligrams per cubic meter (mg/m$^3$). Units of measure for physical agents such as noise are specific to the agent.
A PEL is usually given as a time-weighted average (TWA), although some are short-term exposure limits (STEL) or ceiling limits. A TWA is the average exposure over a specified period, usually a nominal eight hours. This means that for limited periods a worker may be exposed to concentration excursions higher than the PEL, as long as the TWA is not exceeded and any applicable excursion limit is not exceeded. An excursion limit typically means that "...worker exposure levels may exceed 3 times the PEL-TWA for no more than a total of 30 minutes during a workday, and under no circumstances should they exceed 5 times the PEL-TWA, provided that the PEL-TWA is not exceeded." Excursion limits are enforced in some states (for example Oregon) and on the federal level for certain contaminants such as asbestos.
A short-term exposure limit is one that addresses the average exposure over a 15-30 minute period of maximum exposure during a single work shift. A ceiling limit is one that may not be exceeded for any time, and is applied to irritants and other materials that have immediate effects.

## Regulatory agencies for occupational noise exposure
### OSHA

The current PEL for OSHA standards are based on a 5 decibel exchange rate. OSHA's PEL for noise exposure is 90 decibels (dBA) for an 8-hour TWA. Levels of 90-140 dBA are included in the noise dose. PEL can also be expressed as 100 percent “dose” for noise exposure. When the noise exposure increases by 5 dB, the exposure time is cut in half. According to OSHA, a 95dBA TWA would be a 200 percent dose. PEL is exceeded when TWA > 90 dBA. OSHA requires feasible engineering OR administrative controls, and mandatory hearing protection when the PEL is exceeded.

### MSHA

Like OSHA, Mine Safety and Health Administration (MSHA) also uses the same 5 decibel exchange rate and 90 dBA for an 8-hour TWA for their PEL. Once a miner's noise exposure exceeds the PEL, feasible engineering AND administrative controls must be in place to try to limit the noise exposure of the employees. If a mine operator uses administrative controls, procedures for such controls must be posted on the bulletin board and a copy must be supplied to all affected employees.

### NIOSH

The National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL) for noise exposure uses a 3 decibel exchange rate. The recommendation for occupational noise exposure is 85 decibels (dBA) for an 8-hour TWA. For every 3 dB over 85, the exposure time is cut in half. NIOSH reports exposures above this level are considered hazardous. NIOSH uses a hierarchy of control to reduce or remove hazardous noise.

## Chemical regulation for permissible exposure limits

Permissible Exposure Limits are regulatory limits for chemical hazards in a workplace set by OSHA. Organizations may implement stricter guidelines for chemical use and exposure, but OSHA guidelines must be followed at the minimum. Permissible Exposure Limits are time-weighted average, meaning that a worker may be exposed to higher concentrations of the chemical at different times of the work shift.
Many factors contribute in establishing Permissible Exposure Limits. Threshold Limit Values (TLVs), often determined by the American Conference of Governmental Industrial Hygienists (ACGHI), is a key component in determining the PEL. Other things that contribute to determining the PEL are toxicity and particle size.
PELs for chemicals are measured in mg/M$^3$ (milligrams per cubic meter). Mg/M$^3$ is used to measure pollutant’s mass in the air. PELs compliance is monitored through direct reading measurement tools, various sampling methods, and measuring biological markers in workers. Sampling for biological markers may include sampling urine and blood. Direct measurement tools, such as Q-Trak, and indirect measurement tools such as gas chromatography can be used for air sampling.

## Noise Exposure

The Occupational Safety and Health Administration (OSHA) in the United States established the allowed exposure limit for occupational noise at 90 dB and is based on an 8-hour time-weighted average for an 8-hour workday. For worker's safety, OSHA mandates hearing conservation programs when noise levels are higher than 85 decibels. This is dependent on the sector, profession, or nation, different restrictions may apply.
Currently, about 200 million Americans are subject to harmful workplace noise. There are many factors, besides in the workplace, to how noise exposure can affect individuals more or less. These factors can include, but are not limited to, ageing, heredity factors, recreational activities, and some illnesses.
While there are recommendations that exist for noise levels and noise control in communities, there is a lack of general agreement regarding acceptable exposure limits in non-occupational settings or the general environment. To limit noise exposure levels there are several approaches that can be used. One way to limit noise exposure is by wearing personal protective equipment (PPE) such as earplugs, or earmuffs. Another way to limit exposure should be reducing being in environments with heavy amounts of noise exposure. With this in mind it is important to keep individuals informed about prolonged noise exposure.