Moldex 6604 SparkPlugs — NRR 33dB, Uncorded Disposable Foam Earplugs, 200-Pair Box, OSHA 29 CFR 1910.95

Short answer: The Moldex 6604 is a uncorded disposable foam earplug in the SparkPlugs series — NRR 33dB, OSHA 1910.95 compliant, available in a 200-pair box. The multicolor pattern makes earplug compliance visible at a glance — safety supervisors can confirm use across a work floor without approaching each worker individually. With OSHA 50% derating, effective attenuation is approximately 13.0 dB, providing adequate protection in environments up to approximately 103 dB(A). Confirm suitability with noise dosimetry data from your industrial hygiene program.

Moldex 6604 SparkPlugs Uncorded Foam Earplugs — NRR 33dB

Reviewed by the WC Safety Editorial Team — hearing protection specialists with industrial hygiene and occupational health program experience. Last updated: May 2026.

The Moldex 6604 is the uncorded, 200-pair box packaging of the SparkPlugs series — Moldex's soft polyurethane foam disposable foam earplug with a rated NRR of 33 dB. Functionally identical to other Moldex NRR 33 foam earplugs; the SparkPlugs' advantage is high-visibility compliance confirmation. The color mix makes it the standard choice for programs where supervisory auditing is part of the hearing conservation plan. Packaged in a 200-pair box format. See all available formats: Moldex Earplugs at WC Safety → · Earplug Selection Guide →

Key Features — Moldex 6604 SparkPlugs

• The multicolor pattern makes earplug compliance visible at a glance: safety supervisors can confirm use across a work floor without approaching each worker individually.
• Uncorded format — no cord interference for headset or face shield wearers: Uncorded earplugs are preferred when workers also wear communication headsets, neck-mounted equipment, welding helmets, or other gear where a hanging cord creates interference or discomfort
• Box packaging — bulk stock for inventory programs: Standard 200-pair box packaging for storeroom inventory, safety manager distribution, or central issue programs. Store in a cool, dry location away from direct sunlight and chemical vapors
• Disposable single-use design — no contamination risk between workers: As single-use hearing protection, the SparkPlugs eliminates shared-HPD contamination concerns in multi-shift programs. Each worker uses a fresh pair — no shared earplug hygiene issues from shared reusable devices
• OSHA 1910.95 compliance: The SparkPlugs carries an NRR established under ANSI S12.6 testing — meeting the requirements for hearing protective devices under OSHA's Hearing Conservation Standard. Documents provided on request for program compliance files

Applications — When to Use Moldex SparkPlugs Earplugs

• High-visibility compliance programs
• High-headcount manufacturing facilities
• Assembly lines where supervisors audit from a distance
• General industrial and construction
• Any NRR 33 program where earplug use must be easily audited

NRR 33 Noise Reduction — Environment Reference

Using OSHA's 50% derating method, the Moldex SparkPlugs provides approximately 13.0 dB effective attenuation in real-world use:

Estimated exposure uses OSHA 50% derating: (NRR − 7) ÷ 2 = 13.0 dB effective attenuation. Actual attenuation varies with fit quality. Always confirm with industrial hygiene noise dosimetry.

SparkPlugs — Available Formats

Moldex 6604 vs. Alternatives

OSHA Compliance — 29 CFR 1910.95 Hearing Conservation

All Moldex earplugs listed in this collection are hearing protective devices (HPD) evaluated under the ANSI S12.6 standard. The Noise Reduction Rating (NRR) is established per 40 CFR Part 211 (EPA labeling requirements). Under OSHA 29 CFR 1910.95, the employer must implement a Hearing Conservation Program (HCP) whenever workers are exposed to a TWA at or above 85 dB(A).

• Action Level (85 dB TWA): Hearing Conservation Program required — employer must enroll workers in audiometric testing, provide hearing protectors, and conduct annual training. HPD use is voluntary above AL but below PEL
• PEL (90 dB TWA): Hearing protector use is mandatory. The selected HPD must reduce the worker's effective noise exposure to at or below the PEL. With NRR 33 and OSHA derating, effective attenuation is approximately 13.0 dB — meaning the SparkPlugs is appropriate in environments up to ≈ 103 dB(A)
• NRR derating (OSHA recommended method): Effective attenuation = (NRR − 7) ÷ 2. Moldex NRR 33 → (33 − 7) ÷ 2 = 13.0 dB. This is a conservative real-world estimate that accounts for field-use fit variability. Laboratory NRR values consistently exceed field performance
• Dual hearing protection: When noise levels exceed the protection capacity of a single HPD (approximately 103 dB for NRR 33), OSHA requires dual protection — earplugs plus earmuffs. Dual protection adds approximately 5 dB above the higher-rated device alone
• Audiometric testing: OSHA 1910.95(g) requires baseline and annual audiograms for all workers exposed at or above the 85 dB(A) action level. A standard threshold shift (STS) triggers program review and possible HP upgrade
• HPD training: OSHA 1910.95(k) requires annual training covering: noise effects on hearing, earplug selection, fitting procedure, care, and inspection. Training must be documented
• Fit matters as much as NRR: An NRR 33 earplug inserted incorrectly provides less protection than an NRR 25 earplug inserted correctly. Earplug fit testing (individual fit testing, or IFT) is not required by OSHA but is strongly recommended by NIOSH and the NHCA for programs in high-noise environments

Frequently Asked Questions — Moldex 6604 SparkPlugs

What is the NRR and what does NRR 33 mean?

NRR (Noise Reduction Rating) is the attenuation value established by laboratory testing per ANSI S12.6 and required on all HPD packaging by EPA 40 CFR Part 211. NRR 33 means the earplug achieved 33 dB of attenuation under ideal laboratory conditions. OSHA recommends applying a 50% derating for real-world use: (33 − 7) ÷ 2 = 13.0 dB effective attenuation. This accounts for fit variability in the field. In a 100 dB environment with properly fitted SparkPlugs earplugs, your estimated effective exposure is ≈ 87.0 dB — below the 90 dB OSHA PEL.

How do I insert the SparkPlugs correctly?

Roll-down insertion — roll the earplug between clean fingers to a thin cylinder, insert before it expands, hold in place for 20–30 seconds. Proper insertion is the most critical variable for achieving the rated NRR in the field. A poorly inserted earplug can provide significantly less protection than the rated NRR regardless of the earplug's quality. Moldex provides fit-check instructions with bulk packaging; training workers on correct insertion technique is an OSHA-required element of the Hearing Conservation Program under 29 CFR 1910.95(k).

Can I reuse the SparkPlugs?

The SparkPlugs is a disposable earplug. Moldex recommends replacing after each shift or when the earplug is visibly soiled, compressed, or has lost its ability to roll back to shape. Do not wash and reuse disposable foam earplugs — washing degrades the foam matrix and reduces attenuation. Reusable alternatives in the Moldex lineup include the Rockets, Alphas, and Jetz series → for programs targeting reduced disposable waste.

When is the SparkPlugs not sufficient and what do I do?

With OSHA 50% derating, NRR 33 provides approximately 13.0 dB effective attenuation — protecting workers in environments up to approximately 103 dB(A). If your noise dosimetry documents exposures above 103 dB(A), a single earplug is not sufficient. Options: (1) add earmuffs over earplugs (adds ~5 dB above the higher NRR device), (2) switch to a higher-NRR earplug. Engineering controls (noise enclosures, vibration isolation, process modification) should always be evaluated as the primary controls before relying on additional PPE.

What is OSHA's Hearing Conservation Standard and does it apply to my workplace?

OSHA 29 CFR 1910.95 applies to all general industry workplaces where any worker is exposed to a noise TWA at or above 85 dB(A). If your workplace has equipment, processes, or areas generating this level, you are required to implement a Hearing Conservation Program. This includes: noise monitoring, HCP enrollment, audiometric testing, HPD provision, training, and recordkeeping. For construction, OSHA 1926.52 applies. If you are not sure whether your workplace noise levels trigger the standard, contact a certified industrial hygienist for noise dosimetry measurements.

Does the box packaging affect the earplugs inside?

The box packaging keeps earplugs sealed until use. Store boxes in a cool, dry location — avoid direct sunlight, high humidity, and areas with chemical vapors (oil mist, solvents), which can degrade foam. Shelf life for stored, unpackaged foam earplugs is generally 5 years from manufacturing date.