A Fume Hood Is What Type Of Control Method

The concept of a fume hood falls under the category of engineering means of control which manifest through the method of local exhaust ventilation (LEV) in such a way that the concealed airborne pollutants would be removed from the source of emission.

According to the information available presently, a fume hood cannot be identified as an administrative control or personal protection equipment.

In connection with the question of what type of control is a fume hood, this is the answer one would be looking for concerning the type of control being used through fume hood.

The paper is aimed at providing the review of the fume hood control method when it comes to its implementation in laboratories and cleanrooms.

The article will present such specific aspects of the issue as hierarchy, design of containment, exposure control, regulations of OSHA in the sphere of fume hoods and hardware of Deiiang.

Deiiang Cleanroom Technology Co., Ltd. is one of the producers of the device for fume hoods including the exhaust, filtration and monitoring for the fume hood system.

According to the information provided by product designer Jason.peng, Deiiang is not a fume hood builder but a manufacturer of parts only.

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Fume Hood Position in the Hierarchy of Controls

The hierarchy of controls fume hood framework, arranged by comparing all the measures according to their effectiveness, points out that the engineering method of fume hoods use is in the third layer of importance.

The fume hood engineering control method does not eliminate the hazard as it just minimizes the hazard being presented to the personnel working in the laboratory and thus having an exposure.

It is applied ahead of administrative controls and personal protection equipment in case of fume hood.

The point of this section of our article is to investigate the control measures and obtain an explanation of fume hood control being more important than the administrative control and personal protective equipment.

The Standard Hierarchy of Controls Framework

The conventional hierarchy is composed of five levels listed from the strongest to the weakest shelters.

Elimination is the process of completely getting rid of the threat posed. Substitution is replacing the existing opportunity with a more secure one.

Engineering tools ensure that the danger persists but is sequestered from the worker.

The realm of administrative rules incorporates processes of changing work methodologies, trainings, and prevailing schedules.

PPE involves the application of respirators, gloves, and protective eyewear as the final measure against hazards.

In the cleanrooms of pharmaceutical companies, the elimination and modification of the existing substances is prioritized.

On the other hand, in the academic research laboratories, engineering instruments including extraction hoods are the main tools because there is constant rotation of chemicals.

This makes the extraction hoods an efficient device for minimizing the hazards present in the chemical industry.

Fume Hood Classification Within the Hierarchy

Extraction hoods are categorized as engineering controls. They use the system of local ventilation to extract various hazardous materials.

This allows it to rank higher than the administrative and PPE controls. However, it is ranked lower than the elimination and substitution controls in terms of its effectiveness in fighting hazards.

Table 1: Control type effectiveness comparison

Fume Hood as an Engineering Control: Core Mechanisms

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The fume hood engineering control operates through containment and flow of air. Unlike administrative controls, it does not depend on the actions of a worker.

Engineering control involves using local exhaust ventilation. The air is sucked in by the fume hood, goes through the filter, and is discharged outside.

Local Exhaust Ventilation Operating Principle

The local exhaust ventilation fume hood collects airborne pollutants from the origin. The measure of success of operation of a local exhaust hood is the capture velocity.

The face velocity of an ordinary fume hood lies between 0.4 and 0.6 m/s. If the face velocity is lower than 0.4 m/s, the pollutants can escape into the room.

If the face velocity of local exhaust systems exceeds 0.6 m/s, the capture can also fail. When the airflow is very high, it creates whirlwinds that lift the pollutants from the working surface thus making them escape.

To illustrate the principle, let us take the fume hood opening of the size 0.6 m by 1.2 m thus producing the area of 0.72 m².

In order to calculate the exhaust flow required at 0.5 m/s face velocity, the formula, 0.72 multiplied by 0.5 and multiplied again by 3600 would result in the required exhaust flow of 1296 m³/h.

The velocity at which the fume hood picks up air would be dependent on the type of hood, sash opening and influence of cross-drafts. Presence of a door or a fan nearby can affect the efficiency of capture.

According to the opinion of Deiiang designer Jason.peng, air distribution systems near the exhaust hood diffuser within 1 m can severely affect the efficiency of containment measures.

The recommended minimum distance at which the diffusing grid be placed would be greater than 1.5 m from the hood opening.

The ducts produced by Deiiang are designed to ensure the successful operation of air transportation. The professional approACH to producing high quality vents ensures the presence of dampers characterized by up to 0.5% efficiency.

An interactive calculator allows calculating required exhaust flow through the introduction of sash height (in meters), sash width (in meters) and face velocity (in m/s). The result is the amount of exhaust ventilation in cubic meters per hour and CFM.

Fume Hood Containment System Design

A fume hood containment system should comprise of the following items.

• Sash control system - vertical or horizontal sash regulates the area of opening.
• Air barrier system - creates air flow which prevents content escape.
• Baffle design system - distributes the airflow to work bench height.
• Connection to exhaust duct - removes the contaminated air flow away.
• Filtration - it can be HEPA or ULPA.

Bad baffle position is a very frequent factor influencing poor design solutions. There are cases when baffle positioning is done improperly and the result is presence of dead zones with the area of contaminated air.

Due to the Deiiang catalog, all standard dampers are characterized by less than 2% leakage and airtight dampers up to 0.5% (according to JB/T 7228-94 tests).

Chemical Exposure Control Performance of Fume Hoods

Measurement of the fume hood exposure control is considered inward airflow integrity. The efficiency of fume hoods as engineering control measure lies in the capability of fume hood to provide 90-99% efficiency in comparison to absence of any control measures.

Permissible exposure limits, or PELs, as defined by OSHA, establish the baseline for chemical exposure limits.

For example, if a PEL of a chemical is 10 ppm, then the hood must keep the concentration where breathing occurs below that level.

Contaminant Capture and Exposure Reduction Metrics

Face velocity testing measures the inward airflow of a hood, and ASHRAE 110 tracer-gas testing measures the effectiveness of containment. With this information, the typical ratio of exposure reduction can be determined.

Actual exposure reduction ratios depend on the case. The height of the sash above the operating limit, clutter on work surfaces, and rapid movement of the arms can all negatively impact the hood performance.

For example, consider a situation in which without the hood, the exposure level is 100 ppm. With a hood that captures 99% of the exposure, the exposure will be 1 ppm.

The formula for exposure reduction is as follows: (exposure without control minus exposure with control) divided by exposure without control times 100%.

In this case, the calculation is missing one small detail. A reduction ratio of 0.99 corresponds to a 99% capture rate, which means that the different exposure rates will be 100 ppm at first and 1 ppm after.

In the case that the PEL for chemical being considered is 10 ppm, with the hood in place, the exposure must be lower than 10 ppm.

Common Chemical Fume Hood Control Types

The common chemical fume hood control type splits into ducted and recirculating designs, each with its own compatibility range.

Table 2: Comparison between ducted and recirculating fume hoods

Regulatory and Standard Compliance Requirements

OSHA fume hood control requirements can be found in the law body 29 CFR 1910.1450 [1]. According to this law, the company is to conduct performance assessment as described in the Chemical Hygiene Plan.

Standards for cleanrooms and GMPs outline the requirements for airflow and filtration. EU GMP Annex 1 [11], FDA 21 CFR Part 211 [12], iso 14644-3 [7], USP <797> [13] are applicable in controlled environment.

OSHA Fume Hood Control Mandates

According to OSHA 29 CFR 1910.1450, the fume hood control requires the existence of a chemical hygiene plan that will state the frequency of performance assessment for fume hoods [1]. The standard industry practice will be an annual face velocity test.

Plan specification must include annual fume hood testing. The face velocity should be measured and recorded.

Training in sash position and sash proper usage is also obligatory. Thus, OSHA fume hood regulations compliance implies this training.

Verification of such elements as face velocity and glass position should be conducted. Records should be preserved for OSHA examination purposes.

GMP and Cleanroom Fume Hood Standards

• EU GMP Annex 1: conditions for qualifying airflow of sterile manufacture.
• FDA 21 CFR Part 211: good manufacturing practices.
• ISO 14644-3: cleanroom operation.
• USP <797>: sterile preparation procedures.

EU GMP Annex 1 lays out the necessity for unilateral airflow pattern provision in sterile manufacture zones. FDA 21 CFR Part 211 dictates the airflow confirmation documentation policy for ventilation apparatus.

Deiiang H14 HEPA filters conform to EN 1822 efficiency criteria, providing a minimum penetration efficiency of 99.995% as required by EU GMP sterile manufacturing zones [8].

Laboratory Fume Hood Safety: Integration with Other Controls

In laboratory fume hood safety provisions, there is a need for mixing of controls. The fume hood is regarded as the main engineering grade control.

Other levels of administrative as well as PPE controls are necessary for backup. No control method can achieve full effectiveness.

The fume hood containment system may yield under the unclosed sash parameter. The backup is provided by other control layers and PPE.

Complementary Administrative and PPE Controls

• A set of fume hood SOPs.
• Worker training related to face velocity and sash position.
• Use of PPE which is resistant to chemicals (gloves, goggles, lab coat).
• Emergency measures to settle spills and fume hood failures.

The fume hood SOPs and ordinary PPE will suffice for solutions with minor toxicity levels. For carcinogenic and reproductive species, respirators and spill emergency kits are a necessity.

Emergency measures include procedures for cleaning spills, shutting hoods, and conducting evacuations.

The documentation of training and drill execution needs to be carried out for audit purposes.

Routine Performance Verification Practices

A checklist to be followed every day before usage:

It is recommended to carry out the face velocity test at least once annually. The presence of smoke assures that the airflow is moving in the right direction.

Change the filters depending on the pressure drop. HEPA filters register the final resistance at 400-600 Pa.

Jason.peng claims that not sealing the ducts properly while changing HEPA filters is responsible for 30% of failures during maintenance.

Deiiang validation includes monitoring via differential pressure transmitters and PLC. CCY11 differential transmitters offer accuracy at 0.25% FS.

Case study reported by the Project: An analytical chemistry lab at a university used six fume hoods connected to the same exhaust fan.

Deiiang supplied backdraft dampers, pressure relief dampers, CAV valves, silencer and CCY11 differential pressure transmitters.

Results of commissioning showed that all of the six fume hoods were able to deliver air at the recommended rate of plus or minus 3%. The low flow alarm was activated before the airflow got to below 0.4 m/s.

Deiiang Fume Hood Control: Localized Technical Specifications

Deiiang sells product selection, exhaust and control equipment necessary to operate a fume hood.

This section provides information about the listed data for the components of the fume hoods and the cleanroom performance in accordance with ISO standards.

The components of ducts consist of several parts such as dampers used for regulating airflow, allowing air relief, as well as preventing backdraft. In addition to this, devices are used to extract air from the rooms and to connect the duct with the air fan.

Deiiang modular cleanroom panels are available in 11 different patterns, including sizes varying from 2 to 10 square meters. Panel thickness is either 50 mm or 100 mm. Fire resistance is 60 minutes for MGO and 120 minutes for rockwool.

Standard Chemical Fume Hood Core Specifications

Looking through the specifications for chemical fume hoods, we can observe that face velocity varies from 0.4 to 0.6 m/s.

The interior is made of stainless steel 304. Exhaust filters conform to the H14 HEPA. The glass sash thickness is 6 mm. The damper alarming is under 0.5%.

Cleanroom-Grade Fume Hood Performance Data

The cleanroom-grade fume hood performance specifications are highlighted in the table below. The components of the fume hoods are listed along with the specifications and the application of each of the components as indicated in the table.

Table 3: Cleanroom-grade fume hood components

Frequently Asked Questions

What type of control is a fume hood in workplace safety?

The fume hood is a form of engineering control that employs the use of local exhaust ventilation to achieve physical containment. Fume hoods are engineering controls and not administrative controls or PPEs.

Where does a fume hood rank in the hierarchy of controls?

A fume hood is classified as level three in the hierarchy of controls, coming under administrative control and PPE but above elimination and substitution.

What OSHA standards govern fume hood control performance?

The regulation OSHA 29 CFR 1910.1450 is pertinent in this scenario. It mandates that a chemical hygiene plan be in place that identifies the frequency of monitoring. Furthermore, it provides the permissible exposure limits for the substances involved.

Is local exhaust ventilation the same as a fume hood system?

No. The fume cupboard is just one of the types of LEV systems. Local exhaust ventilation is a broader engineering control term, inclusive of other capture systems which are to be used apart from the fume cupboard systems.

Can a fume hood serve as the sole exposure control for toxic chemicals?

No, though the fume cupboard is believed to be the main engineering control system according to the ladder of controls. According to the controls systems, engineering controls need to be supplemented by administrative procedures and proper personal protective equipment.

What is a fume hood containment system designed to prevent?

The fume hood containment system does not allow for the release of the gases to the laboratory working area. The worker is ensured that he or she does not inhale any harmful vapors, and thus does not get in contact with the material if any spillage happens.

References

• [1] OSHA 29 CFR 1910.1450 — Occupational Exposure to Hazardous Chemicals in Laboratories. osha.gov
• [2] EN 14175 — Fume cupboards, Parts 1-7.
• [3] ASHRAE 110 — Method of Testing Performance of Laboratory Fume Hoods.
• [4] SEFA 1 — Laboratory Fume Hoods Recommended Practices.
• [5] ANSI/AIHA Z9.5 — Laboratory Ventilation.
• [6] NFPA 45 — Fire Protection for Laboratories Using Chemicals.
• [7] iso 14644-1 / ISO 14644-3 — Cleanrooms and Associated Controlled Environments.
• [8] EN 1822 / ISO 29463 — High-Efficiency air filters (HEPA and ULPA).
• [9] ISO 16890 — Air Filters for General Ventilation.
• [10] ANSI/ASHRAE 62.1 — Ventilation for Acceptable Indoor Air Quality.
• [11] EU GMP Annex 1 — Manufacture of Sterile Medicinal Products.
• [12] FDA 21 CFR Part 211 — Current Good Manufacturing Practice.
• [13] USP <797> — Pharmaceutical Compounding — Sterile Preparations.
• [14] GB 50243-2016 — Code for Construction and Acceptance of Ventilation and Air Conditioning Works.
• [15] GB 50019 — Code for Design of Heating, Ventilation and Air Conditioning.
• [16] JB/T 7228-94 — Damper leakage classification.
• [17] GB/T 1804 — General tolerances.