Even when our needs are simple, comparing instruments based on manufacturers’ varying and limited specifications can be challenging.
The NIOSH DREAM Team recognized that direct-reading instruments were constantly evolving to meet new user specifications and desires. Participants in the 2008 DREAM Workshop collaborated to define the needs of end-users of direct-reading technology and the desires of manufacturers who produce direct-reading instruments. The team examined then-current uses and needs related to direct-reading equipment and looked ahead to potential future uses and needs.
One of the most important action items identified by the DREAM Team was end-users’ strong need for standardized instrument specifications to help them compare devices. At the same time, instrument manufacturers needed a method of determining these specifications. The team’s goal was to develop a framework format, including standard definitions, to allow all manufacturers to provide information that could be easily compared with that of other manufacturers. The resulting idea was a two-part tool: a form with which manufacturers could list instruments’ specifications in a consistent manner, plus a manual defining the specifications and method of determining them.
Members of AIHA’s Real-time Gas and Vapor Detection Committee, now called the Real-Time Detection Systems Committee, formed a group whose goal was to make the tool envisioned by the NIOSH DREAM Team a reality.
The group formed by the AIHA Real-Time Detection Systems Committee was a consensus-based subcommittee called the Equipment Verification Working Group, which included stakeholders representing equipment manufacturers as well as military, government, academic, emergency response, and commercial end-users. These AIHA committee members have put years of effort into developing forms to document accurate descriptions of detection instruments and detail their capabilities and limitations.
The resulting program, the Standardized Equipment Specification Sheet (SESS), was recently approved by the AIHA Board and is designed to help users of direct-reading gas and vapor instruments make purchasing decisions. For the purposes of the SESS program, real-time gas and vapor detection equipment includes single- and multi-gas instruments capable of detecting oxygen, toxic gases, vapors, and combustibles.
IHs obtain instruments for a variety of uses: personal exposure monitoring, response to a hazardous material incident, or continuous or intermittent area monitoring. In these different scenarios, users may have specific requirements for their instruments such as the capability to provide a warning of a hazardous condition or specific stipulations for accuracy, calibration, or long-term storage. The SESS tool provides information about the specifications for real-time gas and vapor detection equipment in a standardized format to allow for easier product comparisons. The SESS program comprises a manual describing the tool and its use, an instrument specification sheet, and a sensor specification sheet. The concept is similar to the standardized format and information to be included in safety data sheets (SDS). In this case, IHs should be able to use the information in the SESS instrument and sensor sheets to help them decide on the correct equipment to purchase for their anticipated monitoring scenarios.
The SESS manual,
Reporting Specifications for Electronic Real-Time Gas and Vapor Detection Equipment
), was created to provide a standardized approach to the definitions and methods used to develop an equipment specification sheet. Real-time detection equipment specification sheets differ between manufacturers in content, definitions of terms, and methods used to develop specifications. These inconsistencies can lead end-users to misinterpret information provided by manufacturers, which could ultimately increase risk to life and health. The SESS manual is intended to encourage manufacturers to provide key instrument performance characteristics. The manual provides definitions for specifications where appropriate. Any standardized methods recommended for determining the specification parameters are also listed.
The SESS provides common definitions for instrument performance characteristics like start-up time and accuracy. SESS forms are intended to be completed by instrument manufacturers at the request of an IH or anyone interested in purchasing a meter. Ideally, an IH would ask several different manufacturers to complete the SESS for their meters so that the IH could more easily compare one meter against another.
While the SESS program is voluntary, the subcommittee’s hope is that users will begin to request manufacturers to complete the forms. Further, once a manufacturer has filled in the SESS for their meter, perhaps it might make the form available to the public or other IHs who ask about their product.
The two SESS forms are the Instrument Specification Sheet and the Sensor Specification Sheet. One Instrument Specification Sheet could be accompanied by multiple Sensor Specification Sheets, since instruments may be equipped with multiple sensors. Manufacturers should fill out one Instrument Specification Sheet per instrument and as many Sensor Specification Sheets as needed.
The Instrument Specification Sheet is divided into seven sections: General Information, Safety, Maintenance, Data Management, Instrument Performance, Error-state Notification, and Instrument Readings. Overall, this sheet contains 41 specifications; examples include response time (T50), high/low temperature range, calibration interval, factory service interval, and battery operating and recharge time. The Instrument Specification Sheet is available as a
on AIHA's website.
Each sensor in an instrument should be accompanied by its own detailed information found on the Sensor Specification Sheet, a form that also contains seven sections: General Information, Sensor Performance, Sensor Readings, Maintenance, Interferences, Cross-sensitivities, and Additional Information. Several of these sections are also found on the Instrument Specification Sheet because there may be different parameters for the sensor as compared to the instrument.
The two sections that are found only on the Sensor Specification Sheet are Interferences and Cross-sensitivities. In all, the Sensor Specification Sheet contains up to 26 specifications while allowing for additional information. Examples of these specifications include linearity, recovery time, sensor life expectancy, minimum detection limit, and resolution/sensitivity. A
of the Sensor Specification Sheet can be downloaded from the AIHA website.
Industrial hygienists shopping for a new instrument should review the specification sheet provided by the manufacturer. If the sheet has not been created, users should request one from the manufacturer. Ideally, manufacturers should provide the specifications for each sensor type available for the instrument in question. Manufacturers may use one or multiple specification sheets for each instrument or sensor, and their specification sheets should be available on the manufacturers’ websites. If a third party has evaluated an instrument, the manufacturer should provide that reference, if it’s publicly available.
It is the hope of the Real-Time Detection Systems subcommittee that the adoption of the AIHA Standardized Equipment Specification Sheet Program will provide a common language through which the manufacturer and end user can effectively communicate, thus enabling end users to better understand the capabilities and limitations of the instruments and sensors. The members of the subcommittee believe the SESS is valuable in describing detectors not only for gas and vapor, but also for particulate, radiation, vibration, temperature, and other workplace environmental hazards.
The subcommittee welcomes comments and suggestions about the newly approved SESS program from users of instruments and their manufacturers.
is a safety engineer at the Shell Martinez Refinery in California and a member of AIHA’s Real-Time Detection Systems, Ionizing Radiation, and Publications Committees and the Oil and Gas Working Group. He can be reached at
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The Standardized Equipment Specification Sheet (SESS) Program was developed with valuable input from the members of the AIHA Real-Time Detection Systems Committee. Major contributors include Martin Harper, Jack Hill, Edward G. Ligus, Jr., Lee Monteith, Patricia Moser, Patrick Owens, Marc Roe, Terri Pearce, and Jodi Quam.
Industrial hygienists use direct-reading instruments for a variety of purposes, including emergency response, time-weighted average personal exposure monitoring, and measurement of long-term hazardous exposures. While the use of such devices has rapidly increased over the last several years, IHs and related professionals continue to face difficulty in gathering all the information necessary to determine the most appropriate equipment for their work environments. Selection of a direct-reading instrument often comes down to pros and cons, and IHs must choose an instrument based on their prioritized needs and available information about the instrument. But even when our needs are simple, comparing instruments based on manufacturers’ varying and limited specifications can be challenging. Manufacturers provide literature citing the numerous benefits and capabilities of their instruments, but in some cases the information IHs need to make purchasing decisions may not be readily available. And in cases where this information is disclosed, it may be based upon definitions unique to the manufacturer or not defined at all. For example, some manufacturers provide an instrument “TWA” result, but the calculation of this value can vary. Hygienists should obtain from the manufacturer the calculation method before relying upon the TWA result value for determining over-exposure. Other examples of terms with varying definitions among manufacturers include sensor recovery time, T90 (response time), T50 (response time), peak reading, instantaneous reading, accuracy, precision, linearity, drift, and many others. It’s not uncommon for direct-reading toxic gas sensors to have false positive interference gases, but sometimes this information can be found only in a small table at the end of a large user manual. It’s easy to imagine that users who get many false alarms may begin to ignore all alarm events, even ones that are real and dangerous. There have been cases of fires that occurred after a catalytic bead combustible gas sensor (percent LEL) measurement was zero percent LEL. The user may have failed to understand that the LEL sensor requires a certain concentration of oxygen and responds very slowly or not at all to certain large-molecule hydrocarbons. Also, it’s good to know the normal operating temperature and humidity range, and how the instrument will respond when operating outside those ranges. Knowing the instrument’s capabilities based on consistently defined specifications should make purchasing decisions easier and may help avoid serious incidents due to instrument misuse. Recognizing the need for organized research in this area, NIOSH created the Direct Reading Exposure Assessment Methods (DREAM) initiative in 2008. The need for standardized equipment specifications for direct-reading instruments was one among many identified by researchers in the agency’s DREAM program.
Participants from academia, labor, management, governmental agencies, research, and industry, as well as manufacturers and developers, met in November 2008 in Arlington, Va., at the DREAM Workshop to discuss needs in the area of direct-reading methods for assessing occupational exposures. During that meeting, which was co-sponsored by AIHA and 11 other organizations, attendees addressed direct-reading exposure assessment methods for a variety of occupational hazards, including aerosols, gases, vapors, ergonomics, noise, radiation, and surface sampling and biomonitoring. The workshop was intended to help participants describe the important information related to the art and science of real-time assessment of worker exposure, determine whether direct-reading methods are available for exposures of interest, identify gaps in technology for real-time exposure methods, and specify agendas for research of direct-reading methods for different classes of occupational hazards.
American Chemical Society:
Chemical Hazards in the Workplace
, chapter 31, “
Statistical Protocol for the NIOSH Validation Tests
” (April 1981).
2008 Direct-Reading Exposure Assessment Methods (D.R.E.A.M.) Workshop
Components for Evaluation of Direct-Reading Monitors for Gases and Vapors
” (July 2012).
NIOSH: “Development and Validation of Methods for Sampling and Analysis of Workplace Toxic Substances” (
, September 1980).
The SESS program team also consulted definitions from traditional industrial hygiene textbooks such as
The Occupational Environment: Its Evaluation and Control and Management
(AIHA) and
Fundamentals of Industrial Hygiene
(National Safety Council) as well as documents and webpages published by federal OSHA, NIOSH, the International Safety Equipment Association (ISEA), the National Electrical Manufacturers Association (NEMA), and EPA.
How to Use the AIHA Standardized Equipment Specification Sheet