Sheet 18Domain 3 of 5 · Health Hazards and Basic Industrial Hygiene
Silica, lead and chemical exposure: STSC industrial hygiene
Respirable crystalline silica in construction is limited to 50 µg/m³ as an 8-hour average under 29 CFR 1926.1153, and lead carries the same figure under 29 CFR 1926.62. This sheet sets those limits beside the other agents a construction supervisor deals with, from asbestos to carbon monoxide and hydrogen sulfide, explains the words used to describe exposure, and gives you practice cards on choosing controls.
Permissible exposure limit: OSHA's legal limit, usually as an 8-hour average.
REL
Recommended exposure limit from NIOSH. Advice, and not enforceable.
TLV
Threshold limit value from the American Conference of Governmental Industrial Hygienists (ACGIH). A professional guideline.
Action level
A level below the PEL that switches on extra duties under a substance standard, such as periodic monitoring. Usually half the PEL; lead is the exception, at 30 against a PEL of 50 µg/m³.
TWA
Time-weighted average: exposure averaged over a shift, normally 8 hours.
STEL
Short-term exposure limit: a 15-minute average.
Ceiling
A level that may not be exceeded at any moment.
IDLH
Immediately dangerous to life or health: a level that could kill, cause lasting harm or keep a worker from escaping.
Talking point 02
Check yourself on exposures
Silica, lead, asbestos, solvents, isocyanates and welding fume, in site scenes and a few straight definitions.
Card 1 of 16 · 0 right
Card 1
Why might a contractor choose to control a solvent exposure to the current ACGIH TLV rather than the OSHA PEL?
Pick an answer. A short note for each option, A to D, appears here.
ACorrect: Most construction PELs were adopted around 1970 and seldom updated, while TLVs are revised as new health data appear.
BBoth TLVs and PELs include 8-hour averages, short-term limits and ceiling values, so they do not split by task length.
COSHA enforces its own PELs and does not require using the lower of the two limits.
DACGIH TLVs are voluntary guidelines and are not enforceable on any project unless a contract adopts them.
Card 2
A crew is scraping lead-based paint from a steel bridge. Where and how should the supervisor have them eat lunch?
Pick an answer. A short note for each option, A to D, appears here.
AHand sanitizer does not remove lead dust, so the crew can still swallow lead from their hands while eating.
BCorrect: Lead is swallowed from contaminated hands and food, so eating requires a lead-free area and washing hands and face first.
CEating in work clothing brings lead dust close to the food and mouth.
DEating at the work area, even without gloves and coveralls, exposes food to lead dust in the air and on surfaces.
Card 3
A crew will run a gasoline-powered concrete saw inside a partly enclosed parking-garage level. Which control is the MOST effective way to prevent carbon monoxide overexposure?
Pick an answer. A short note for each option, A to D, appears here.
AOrganic-vapor cartridges do not remove carbon monoxide, which needs supplied air if a respirator is used.
BCorrect: An electric or battery saw eliminates the exhaust source, which ranks above ventilation, rotation and respirators.
CRotation shortens each person's exposure but does not lower the CO level, and nearby workers stay exposed.
DFans and open ramps help, but in partly enclosed areas CO can still build to dangerous levels.
Card 4
A crew will cut concrete block with a handheld masonry saw for several days. Which control should the supervisor implement FIRST to limit silica exposure?
Pick an answer. A short note for each option, A to D, appears here.
ARotation spreads the exposure over more workers instead of reducing dust at the source.
BDry cutting with a fan blows silica dust toward others and is not an accepted dust control.
CRespirators are the last line of defense and are used in addition to, not instead of, engineering controls.
DCorrect: Integrated water delivery suppresses dust at the blade, the engineering control the silica standard's Table 1 lists for handheld masonry saws.
Card 5
A welder works under a local exhaust hood mounted about 3 feet above the arc, and fume is still rising past the welder's face. What is the BEST corrective action?
Pick an answer. A short note for each option, A to D, appears here.
ARunning the fan between shifts does nothing to capture fume while the welder is working.
BGeneral ventilation dilutes fume across the room but does not stop it rising through the welder's breathing zone.
CA respirator is the last line of defense and leaves the poorly placed hood uncorrected.
DCorrect: Capture velocity drops sharply with distance, so a local exhaust hood must sit close to the arc to pull fume away.
Card 6
During a renovation, a crew will remove vinyl asbestos floor tile and its mastic. Under the construction asbestos standard, what class of work is this?
Pick an answer. A short note for each option, A to D, appears here.
AClass IV covers maintenance and custodial cleanup of asbestos debris, not removing flooring.
BClass III is repair and maintenance work where asbestos is likely to be disturbed, not full removal.
CClass I covers removal of thermal system insulation and surfacing material, not floor tile.
DCorrect: Class II is removal of asbestos-containing material that is not thermal system insulation or surfacing, such as floor tile and mastic.
Card 7
A crew will remove lead-based paint from bridge steel by abrasive blasting. Until exposure monitoring shows otherwise, what exposure must the employer assume?
Pick an answer. A short note for each option, A to D, appears here.
APresumed exposures for these lead tasks all start above the PEL, so the action level is never the assumption here.
BAbove 10 times the PEL is the tier for tasks such as rivet busting and power-tool cleaning without dust collection.
CCorrect: The lead standard presumes abrasive blasting, welding, cutting and torch burning exceed 50 times the PEL until monitoring shows otherwise.
DAbove the PEL but below 10 times is the tier for manual scraping, manual sanding and heat-gun use.
Card 8
What is the primary health hazard associated with isocyanates used in spray polyurethane foam insulation?
Pick an answer. A short note for each option, A to D, appears here.
AEye irritation can occur, but the main concern with isocyanates is an allergic response of the lungs.
BIngestion is not the main route on a spray foam job. Isocyanates are mainly an inhalation hazard.
CIsocyanates can irritate or sensitize skin, but they are not mainly known for burns. The lungs are the main concern.
DCorrect: Isocyanates are strong respiratory sensitizers. Once a worker is sensitized, even small exposures can trigger occupational asthma.
Card 9
Under the construction silica standard's scheduled monitoring option, a worker's initial sample shows 35 µg/m³. When must monitoring be repeated?
Pick an answer. A short note for each option, A to D, appears here.
ACorrect: A result at or above the 25 µg/m³ action level but at or below the PEL must be repeated within 6 months.
BBeing under the PEL does not end monitoring; it stops only after two results below the action level.
CTwelve months is not a repeat interval in the construction silica standard's scheduled option.
DThree months is the repeat interval for results above the 50 µg/m³ PEL.
Card 10
A concrete finisher kneels in fresh concrete all morning in ordinary work pants. That evening the knees are red and blistered. What MOST likely caused the injury?
Pick an answer. A short note for each option, A to D, appears here.
ARough aggregate can scrape skin, but abrasions do not usually show up as burns hours later.
BAllergic cement dermatitis comes from hexavalent chromium, and silica is mainly an inhalation hazard.
CCorrect: Wet cement is strongly alkaline, and long contact through soaked clothing causes chemical burns that often appear hours later.
DConcrete releases only mild heat as it cures, not enough to cause thermal burns through clothing.
Card 11
Which situation is BEST suited to general (dilution) ventilation rather than local exhaust ventilation?
Pick an answer. A short note for each option, A to D, appears here.
AStainless steel fume contains hexavalent chromium, so it should be captured at the source.
BCorrect: Dilution ventilation suits low-toxicity contaminants released slowly over a wide area, where capture at one point is impractical.
CA grinder throws silica dust right at the worker, which calls for capture at the tool or water control.
DA highly toxic contaminant from one fixed point is the classic case for local exhaust.
Card 12
A welder will spend the next week welding stainless steel. Which hazardous agent makes this work more hazardous than welding plain carbon steel and needs specific controls?
Pick an answer. A short note for each option, A to D, appears here.
AZinc fume comes from welding galvanized steel and causes metal fume fever; it is not the stainless steel hazard.
BCorrect: Stainless steel contains chromium, and welding it creates hexavalent chromium, a carcinogen with its own construction standard.
CLead fume comes from coatings on painted steel, not from the stainless steel itself.
DIron oxide fume forms in most steel welding, so it does not explain the added hazard of stainless.
Card 13
Before renovating a 1975 office building, a crew will disturb old pipe insulation that has not been sampled. How must the insulation be treated?
Pick an answer. A short note for each option, A to D, appears here.
AUnlabeled insulation can still contain asbestos, so the lack of a label proves nothing.
BCorrect: Thermal system insulation in buildings built before 1981 is presumed asbestos-containing until testing shows otherwise.
CIntact material can release fibers once it is disturbed, so its condition alone does not decide how it is treated.
DBans on some spray-applied asbestos did not remove it from other products, and pipe insulation from that era often contains it.
Card 14
Asbestos exposure combined with cigarette smoking raises lung cancer risk far more than the two risks added together. What is this type of interaction called?
Pick an answer. A short note for each option, A to D, appears here.
AAn additive effect equals the simple sum of the two risks, which understates this combination.
BAn antagonistic effect is one where one agent reduces the effect of the other.
CCorrect: A synergistic effect is one where the combined risk is much greater than the sum, as with asbestos and smoking.
DPotentiation is when a substance harmless alone makes another more toxic, but smoking causes lung cancer on its own.
Card 15
During an industrial hygiene survey on a construction site, which method is most reliable for detecting exposure to airborne particulates that could lead to respiratory issues?
Pick an answer. A short note for each option, A to D, appears here.
AOld data may not match today's tasks, materials or controls. Current exposure needs current sampling.
BArea samples taken away from workers can miss what each worker actually breathes during the task.
CSettled dust shows that dust is present but cannot measure the respirable dust a worker inhales.
DCorrect: A sampler worn in the worker's breathing zone measures what that worker actually inhales over the task or shift.
Card 16
Under the construction silica standard, which workers must be offered medical surveillance?
Pick an answer. A short note for each option, A to D, appears here.
ASurveillance is triggered by required respirator use, not by symptoms, which often appear only after lasting lung damage.
BAn action-level trigger belongs to the general industry silica rule, and even there it counts 30 or more days a year, not a single day.
CDoing silica tasks with Table 1 controls that need no respirator does not by itself trigger surveillance.
DCorrect: the construction silica rule requires medical surveillance for workers who must wear a respirator for 30 or more days a year.
Blood lead is measured in µg/dL, and removal from exposure starts at 50 µg/dL
Asbestos
0.1 f/cc; excursion limit 1.0 f/cc over 30 minutes
29 CFR 1926.1101
The work class follows the material and the activity, whatever the fiber count
Hexavalent chromium
PEL 5 µg/m³; action level 2.5 µg/m³
29 CFR 1926.1126
Action level at half the PEL
Carbon monoxide
50 ppm
29 CFR 1926.55, Appendix A
NIOSH recommends 35 ppm
Hydrogen sulfide
10 ppm
29 CFR 1926.55, Appendix A
General industry uses a 20 ppm ceiling
µg/m³ = micrograms per cubic meter of air; f/cc = fibers per cubic centimeter; ppm = parts per million; µg/dL = micrograms per deciliter of blood.
Talking point 04
Task first, chemical second
The cards on this sheet start from a task: cutting, grinding, blasting, spraying, welding or tearing out. Work out what the task releases and how it reaches the worker. Inhalation is the usual route on a jobsite; ingestion, absorption through skin or eyes, and injection complete the list.
Control choices follow the hierarchy of controls. Block ordered pre-cut to size at the yard takes a saw cut, and its dust, off the site before anyone needs a mask.
Hazard communication runs under all of it: the label and the SDS are where you read what a product is. The HazCom, SDS and labels sheet covers the 16 SDS sections and the pictograms.