# Calculations

## Anticipate, Identify, Recognize

When starting an occupational exposure assessment, the first step a practicing industrial hygienist must do is be able to anticipate, identify, and/or recognize workplace hazards so that stressors that may impact employee health can be evaluated later in the assessment. Understanding the workplace, how chemical and physical agents are generated and the existing control measures (e.g. engineering controls) in place, help the industrial hygienist to develop an effective plan for evaluating risks.

## IHEST – Industrial Hygiene Exposure Scenario Tool

AIHA has released the free IHEST (Industrial Hygiene Exposure Scenario Tool) which helps an industrial hygienist to identify and capture basic exposure potential data, for the purpose of improving evaluation accuracy in the assessment process. The tool includes prompts for:

• Process Overview
• Exposure Controls
• Similar Exposure Groups
• Ventilation
• Room layout
• Airborne concentrations
• Dermal exposures, and
• Noise exposures

Download a copy of the AIHA IHEST from AIHA’s website or without macros below.

Source: AIHA

## Statistical Analysis of Health & Safety Data – IHSTAT

Are you looking for statistical analysis of health and safety data (e.g. number of measured occupational exposures that exceed established OELS)? Take a look at OHShub.com’s post on IHSTAT, where you can download AIHA’s excel worksheet that can perform some basic statistics for you.

## AIHA Releases IH Calculator App

AIHA recently released the free IH Calculator LITE  app, a calculator that aids industrial hygienists in performing OH&S calculations quickly and efficiently on their mobile device.  Topics include: Noise, Heat Stress, Ventilation, Exposure Assessment and is complimented with a range of conversions such as volume, distance, pressure, temperature, TLVs, and more.  The app is currently only available on Apple products (iOS).

Source: AIHA

## Calculator: Minimum Sample Volume & Required Sampling Time

Want to determine the Minimum Sample Volume needed to ensure you collect enough of a sample volume so that the results are capable of being less than the Exposure Limit? Want to know how long you need to sample at a given flow rate?

If so, use OHShub.com’s Minimum Sample Volume and Required Sampling Time calculator and take the guess-work out of the equation.

Input the:

• Laboratory Limit of Quantitation (LOQ)
• Exposure Limit
• Desired Fraction of the Exposure Limit (essentially a safety factor for sampling)
• Sampling Rate

And the results will give you the Minimum Sample Volume and Required Sampling Time.

Note:  Ensure that you have the right units and all of the units are consistent.  Units such as parts per million (ppm) for Exposure Limits may need to be converted to mg/m3.

Calculator: Minimum Sample Volume and Required Sampling Time (35.0 KiB, 3,865 hits)

## NTP (Normal Temperature & Pressure) Definitions

A few questions have arisen regarding the term NTP (Normal Temperature and Pressure).  The following table helps to sort any potential confusion.

 Agency Pressure Temperature Traditional (Chemistry/Physics) 29.92 “Hg 760 mm Hg 492 ˚R 273 ˚K ACGIH (TLV) 29.92 “Hg 760 mm Hg 530 ˚R 298 ˚K NIOSH/AIHA (Traditional) 29.92 “Hg 760 mm Hg 537 ˚R 298 ˚K ASHRAE (Ventilation) 29.92 “Hg 760 mm Hg 528 ˚R 293 ˚K

## Worksheet: Analyzing Lifting Operations

Washington’s Department of Labor and Industries has created a worksheet based upon the NIOSH Lifting Equation to determine if a lift operation exceeds the recommended limits.  A copy of this worksheet can be found here:

Worksheet: Ergonomics Calculations (40.8 KiB, 1,453 hits)

.  If you are unfamiliar with the NIOSH Lifting Equation, a good resource is the Revised NIOSH Lifting Equation Document.

LI = the relative estimate of the physical stress associated with a manual lifting job

Sources:  eLCOSH & NIOSH

## IHSTAT – Statistical Analysis of Health & Safety Data

IHSTAT is a excel worksheet that enables statistical analyses of occupational hygiene measurement data and compliance testing (with occupational exposure limits).  IHSTAT was developed by AIHA (American Industrial Hygiene Association).

1. Determines whether samples are normally distributed or log normally distributed.
Where:
• Normal distribution – data that clusters around a mean/average
• Log Normal distribution – the logarithm of data is normally distributed
2. Determines percentage of samples that exceed the occupational exposure limit.

## November 2009 CIH Exam Prep Questions

CIH Exam Prep Questions for November 2009 have been posted.  34 questions covering a range of Industrial Hygiene and Safety topics were put together by OHShub.com to test your knowledge.  Any questions, please don’t hesitate to ask!

You can view the quiz HERE

When you complete the quiz, please put the number of questions you got correct in the comments section of this post.  Thanks!

## CIH Exam Preparation Questions Coming to OHShub.com

Monthly questions for individuals planning to take the Certified Industrial Hygiene examination will be posted on OHShub.com beginning November 1, 2009.  Approximately 30-50 questions will be posted monthly and will cover the rubrics as defined by the American Board of Industrial Hygiene (ABIH).

Whether you are looking to sit for the exam, brush up on some knowledge, or show your expertise, visit OHShub.com and show us what you have got!

Good luck!

OHShub.com

## Calculators: Injury and Illness Incidence Rate & DART

Want to calculate your Injury and Illness Incidence rate (I&I) and/or your Days, Away, Restrictions and Transfers (DART) rate? Use OHShub.com’s Incidence Rate and DART Rate calculator (Excel spreadsheet format) to determine your rates.

DART Rate Calculator (42.0 KiB, 1,777 hits)

Sample Screenshot IR & DART Calculator

## Combined Toxic Effects of Chemicals

Below is a summary of some of the very similar methods and rationale used by agencies to assess the combined toxic effects of chemicals.

ACGIH
Source: TLV’s and BEI’s Publication

• Recommends an additive (combined) approach for two or more substances that affect the same target organ/system
• The ratio of the exposure concentrations are summed together
• where: C = observed concentration, t = TLV

• If the sum exceeds one, the TLV for the mixture is considered to have been exceeded
• Additive formula applies to simultaneous exposures for hazardous substances with TWA’s, STEL’s, Excursion Limits, and/or Ceiling Limits. Bases (TWA’s, STEL’s, etc.) should be kept consistent, as feasible
• Exceptions are made when it is believed the major effects of the chemicals are not additive or possibly when the mixtures contain carcinogens
• Synergistic effects should be carefully considered

OSHA
Source: 29 CFR 1910.1000

• Recommends an additive (combined) approach for two or more substances that affect the same target organ/system
• The ratio of the exposure concentrations are summed together
• where: C = observed concentration, t = TLV

• If the sum exceeds one, the TLV for the mixture is considered to have been exceeded
• Approaches to chemicals with similar effects are not restricted

NIOSH
Source: NIOSH Methylene Chloride Intelligence Bulletin

• Recommends an additive (combined) approach for two or more substances that affect the same target organ/system
• The ratio of the exposure concentrations are summed together
• where: C = observed concentration, t = TLV

• If the sum exceeds one, the TLV for the mixture is considered to have been exceeded
• Specifically addressed methylene chloride in the presence of carbon monoxide due to the formation of carboxyhemoglobin

Other Agencies

ATSDR

• Typically a semi-quantitative screening process using flow-chart methodology
• Useful:
1. when exposures to the components are not clearly hazardous when considered singly, but potentially
hazardous due to additivity or interactions when considered together
2. when the community-specific health outcome data indicated that the site might have an adverse
impact on human health, but the exposure-based assessment of each separate component did not
3. when the health outcome data were ambiguous or did not indicate an adverse impact on human
health, but the exposure-based assessment identified a potential hazard from one or more of the
components.
EPA

• Consistent with the ASTDR approach

## Adjusting Occupational Exposure Limits for Extended Work Shifts

OSHA currently has two standards in which the PEL is adjusted based on the length of the work shift, both of which are lead standards:

All other PELs are based upon 8-hour time weighted average (TWA), a short term exposure limit (STEL), or a ceiling limit (C).

The lead PEL of 50 micrograms per cubic meter (ug/m3) is adjusted in accordance with the following formula:

New PEL = 400/hours worked during shift

e.g. If an employee works a 10 hour shift, the PEL is reduced from 50 ug/m3 to 40 ug/m3

Additionally, as discussed in OHShub.com‘s post PEL Adjustments for Extended Work Shifts – Noise, the Action Level for noise must be reduced for extended work shifts based on the following formula:

New AL (dBA) = 90 + 16.61 x log (50 / (12.5 x number of hours worked))

e.g. If an employee works a 10 hour shift, the PEL is reduced to 83 dBA

From a recommended practice standpoint, the Brief and Scala model provides a easy method of reducing exposure limits and is noted ACGIH’s TLVs and BEIs documentation. The Brief and Scala model provides a reduction factor via the following formula:

Reduction Factor = (8 x hours worked in shift) x ((24 – hours worked in shift) / 16)

It should be noted that the Brief and Scala model should not be used to justify very high exposures for short durations.

e.g. If an employee works a 10 hour shift, the reduction factor is 0.7. Multiply 0.7 times to the Exposure Limit to determine the recommended limit using the Brief and Scala model.

Additionally, it should be noted that OSHA does have PEL adjustments for cotton dust, but only when employees are required to wear respirators to reduce their respective exposures.

## PEL Adjustments for Extended Work Shifts – Noise

The purpose of this memorandum is to resolve issues concerning adjustments of the PEL during extended work shifts. This applies for exposures to the noise levels of Table G-16 of 29 CFR 1910.95 or substances found in Subpart Z. Current OSHA policy requires only the action level to be reduced for exposures to noise during extended work shifts; the PEL is not required to be adjusted. The only standards which require PEL adjustments are the lead standards in construction and general industry. These standards have a specific provision which requires work shift adjustments. Existing policy for Occupational Exposure to Cotton Dust also has a requirement to adjust extended work shifts when employees are required to wear respirators for a portion of the work shift to reduce their level of exposure, as set forth in the Federal Register, Vol. 45, No. 251, pp. 85736-85739. The contribution that the extended work hours adds to employee exposure must be included in calculating the required time respirators must be worn during the shift.

As stated in a previous memorandum dated November 8, 1996:

Compliance officers can choose one of two approaches for employees who work extended work shifts beyond 8 hours. The choice taken will depend on the nature of the hazardous chemical.

1. The first approach is to sample what the compliance officer believes to be the worst continuous 8-hour work period of the entire extended work shift.
2. The second approach is to collect multiple samples over the entire work shift. Sampling is done such that multiple personal samples are collected during the first 8-hour work period and additional samples are collected for the extended work shift. Unless a compliance officer is dealing with lead, the PEL in this approach is calculated based upon the worst 8 hours of exposure during the entire work shift.

We hope you find this clarification helpful. If you have any questions or if we can be of any further assistance, please contact the Office of Health Enforcement at (202) 693-2190.

A link to the memo can be found HERE